Compost on clay soil

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Compost on clay soil



If you have heavy clay soil you may find the going is tough when you try to dig it over and try to grow anything in it. You may may feel that the best thing you can do is to just grow grass on it and forget about growing anything else. One thing that will help is compost.

All soil types will benefit from the addition of compost. Introducing compost on clay soil will make more of an improvement than on any other soil type. If you have clay soil, adding compost is an ideal form of organic matter.

If you have a good supply of compost available and you have clay soil then put as much of it on the soil as possible. Clay soil is crying out for as much organic matter as it can get. Adding compost to clay soil will always help to break up those lumps that are so hard to work with. You don’t need to dig it in. Sometimes it’s better if you don’t.

What else?

  How can I make my soil drain better?    Is Gypsum good for clay soil? 

How do you break up clay soil?    How can I improve my clay soil? 

Burning clay soil  What plants grow well in clay soil?   

What organic matter to add to clay soil?    How do you dig through clay?   

What grass grows well in clay soil?    What is the average PH of clay soil?  

Why is clay good to have in your soil?    What fertilizer is best for clay soil?   

What is a fish emulsion?    What crops can be grown in clay soil?   

Is peat moss good for clay soil?    What creates clay?   

How much lime should be added to soil?    What does clay soil feel like?   

How can we improve the soil?

 

What is heavy clay soil?

But first you need to identify if you have clay soil. If you walk on wet dug-up soil and you find that so much of it gets stuck to your boots that you can hardly walk then you have clay soil. If when you go to wash those boots and it takes a strong pressure hose to remove it then you have clay soil.

Adding compost, or any organic matter, to clay soil can only improve it. Organic matter will attract worms and all soils benefit from a strong population of worms. If there are no worms in the soil then the soil can’t ‘breath’. Plant roots need air and worms open up corridors that allow air in.

Encouraging conditions where air can move through the soil will also help with decomposition of organic material. Air movement in soil will assist with drying. After long periods of wet weather, clay soil will be saturated and, because of the nature of clay soil, will hold onto the moisture for longer than is needed.

Clay soil is much harder to manage than any other soil. You need to understand it and how it responds to wet or dry weather. In wet conditions you must stay off clay ground. So if you find yourself having to clean off a lot of clay from your boots, then it means that you shouldn’t have been walking on it.

You can do a lot of damage in terms of compaction to clay soil if you try to dig it if the soil is damp. In damp conditions clay soil will smear and become capped. This will prevent the free movement of air and reduce drainage. Without air and moisture having free movement, the roots of plants will become waterlogged and suffocate. It’s a little known fact but plant roots do need some air.

On the other end of the scale, if clay soil becomes very dry, then you will find it difficult, if not impossible, to dig. Clay soil has a habit of becoming lumpy. These lumps, when dry, will become so hard that it’s like trying to break up concrete.

To get the best from clay soil you need to monitor it very closely. After a period of wet weather leave it alone long enough to dry out but don’t leave it too long. There is a near critical point when clay soil is dry enough but not too dry to be able to dig and get a good tilth for small seeds to germinate.


How can I make my soil drain better?

In agriculture it’s possible to manage heavy clay soil by performing what’s known as ‘subsoiling’. This is where a deep cultivator is pulled through the soil to a depth of 30 inches or more. This has the effect of breaking up the subsoil deep down allowing excess water to drain away. In a garden situation it’s possible to get the same effect but it does require a lot of work.

You can obtain deep drainage for a specific row of vegetables, eg. runner beans. Before you attempt this you must ensure that the ground conditions are suitable.  It is vital that you don’t try to dig clay soil when it’s wet or even damp. Digging wet or damp clay soil will smear it and it will make in lumps which will set like concrete.

Begin by cultivating the strip of ground that you want for growing the crop using a rotavator. Then dig out the the loosened soil completely leaving a clean trench. Then cultivate the floor of the trench with the rotavator, digging it as deep as possible.

Then back fill with the soil that you removed. After this amount of digging you should now have a reasonable tilth on the surface and a good depth of soil that is open enough to allow adequate drainage.

Is Gypsum good for clay soil?

Yes it is. The including of gypsum granules will create open pockets in the soil which will improve the soil structure. A more open structure will allow for more effective draining of surplus water. There is also the added bonus of easier air movement through the soil which will be of benefit to plant roots.

These effects won’t happen straight away. It will take a sustained approach of applying gypsum over a few years before you will see any noticeable effect. Applying gypsum is easy to do and is a relatively cheap way to improve the heaviest of clay soils.

The adding of gypsum is not a substitute for adding organic matter like compost. Adding organic matter is by far the most preferable approach to making the best of heavy clay soil. A well made compost will introduce life into the soil and open it up. It will also attract a healthy population of worms.

It isn’t just compost that will have this effect. You can add tree bark, wood chip or sawdust but be aware that these may not be fully decomposed like compost. When any organic matter continues to decompose in the soil, it tends to have the detrimental effect of taking valuable nitrates out of the soil. These are nitrates which the growing plants need.



There is only one way to avoid this. Materials like wood chip, for example, can be stored in a compost bin to rot down, ideally to the point of being black before being added to the soil. If you have a bin full of just wood chip or sawdust, add water regularly because these materials tend to be dry. To ensure that decomposition takes place it needs to be kept moist.

There is no such problem of nitrates being used up when adding gypsum. It’s a rock mineral that’s inert. There is a limited amount of calcium and sulphur available from it but its main role is to enhance the soil structure and no more. It doesn’t reduce or contribute to soil acidity.

If you haven’t got enough organic material to tackle a large area of heavy clay soil and no prospect of getting enough then applying gypsum will be the best thing you can do.

Some will tell you that you can just spread gypsum granules on the surface and no more action is required. For it to do any good it has to be incorporated into the soil. It has to become part of the mix or it won’t achieve anything. So this requires some digging over but don’t forget, this is heavy clay soil which can only be worked when the conditions are right.

Only dig clay soil after a period of dry weather when the the soil is slightly moist but not too dry. Handling clay soil is an art which you have to get a feel for but you do need to incorporate the gypsum into the soil to get the desired effect.

What does Gypsum do to the soil?

As mentioned, gypsum will do much to improve soil structure and, in addition, there is an interesting chemistry that will enhance clay soil.

Gypsum contains calcium and sulphur. Some of this is sufficiently soluble to become available to plant roots. The calcium has the added property of playing a part in the flocculation of clay. This is when clay particles are become attached together in small collections which improve the overall structure of the soil.

Gypsum will reduce excessive levels of sodium in the soil. This is often referred to as ‘sodic’. The effect of adding gypsum replaces the sodium that is attached to the clay particles with the freely available calcium in the gypsum. In the removal process the sodium combines with the sulphur, which is also available from the gypsum, and becomes a sodium sulphate compound.

This becomes a free floating molecule which can then drain away from the scene. The process changes the structure of the soil making it more open and free draining. The problem-causing sodium can then become removed by drainage in solution thus permanently improving the soil structure.

With this change having been made the soil structure departs from the complications that are associated with heavy clay soils. This is relevant in wet weather when the soil surface can become capped or crusted when dry weather follows wet. The surface can set like concrete. It makes the soil almost totally impermeable to both water and air. As a result the roots of plants can’t make progress and this is why plants in untreated heavy clay soil look so poor.

The same problem inhibits the progress of seedlings trying to push through. The adding of gypsum will positively affect the soil structure to prevent the capping.

How much gypsum to apply

With gypsum being available as a granular particles it’s easy to apply. You just need to scatter it over the soil surface and aim for a rate of approximately 15lb per hundred square feet as a guide. If you know that you have heavy clay soil and nothing like enough compost or other organic material, plan to add gypsum at the 15lb rate for 2 or 3 consecutive years.

If the soil is particularly dry at the time of application it may help to add some water after you’ve mixed the gypsum into the soil. But if there is imminent rain forecast then this shouldn’t be necessary.

How do you break up clay soil?

We could also ask what will breaks up clay soil? By ‘break up or break down’ we mean working the soil to a tilth that allows the sowing of seeds, then there are two approaches that work very well. The first involves digging and physically breaking apart the lumps. This is a lot of hard work and you need to do it when the conditions are right.

If the clay soil is wet then you mustn’t do anything with it because if you do it will become ‘smeared’ into sticky lumps which will then dry and become hard, like concrete. This will make clay soil even harder to break up. Catching the right time to work clay soil will come with practice and close observation.

Another approach is to let the winter elements do some of the work for you.

This can only work if you live in a part of the world where you have, at least, a chance of some frosty weather during the winter months. For this you need to plan long-term. It involves digging over the soil and leaving it over the winter.

For this the digging process can be done when the soil is damp. It’s not as critical as for preparing a seed bed. The lumps of soil will freeze and then thaw. The action of freezing and thawing will break up hard lumps of clay. This is a very convenient way of working heavy clay soil. You don’t need to do anything.

It’s better if you leave it to this natural method of soil break up. In a hard Winter will happen over and over again. The effect will then be that the big lumps will disintegrate into much smaller particles. Soil break up this way will avoid the compaction that can happen when we use cultivating tools.

When the Springtime comes and you want to start preparing this ground for seed sowing, all you will need to do is dig it over enough to establish a good tilth. Remember that this is still heavy clay soil so you need to leave it and make a judgement as to when the conditions are right. With some planning the winter frosting approach will get you off to a good start when managing clay soil.

How can I improve my clay soil?

Apart from the aforementioned, inclusions of lots of organic material e.g. compost or the mixing in of gypsum, there’s an ingredient that will help you to get the most out of clay soil. The adding of hydrated lime will improve any clay soil.

Heavy clay soil tends to have a high level of aluminium (Al) in it which can be toxic to most plants if the soil is at all acidic. The adding of hydrated lime will neutralize the acidity and disperse this toxic element.

There isn’t much more that you can do to improve clay soil. Most of the time it’s a matter of damage limitation. The main thing being that you must do all that you can to avoid doing anything that’s detrimental to the structure which basically means avoiding compaction. The best way to achieve this is to keep off it when it’s wet or even damp.

Burning clay soil

If you’re really frustrated by your heavy clay soil then there is an ultimate solution that will bring you a satisfactory conclusion. Yes you can burn clay soil. This doesn’t mean that the soil itself actually burns. There is nothing in clay soil that could be used as a fuel. What’s being suggested here is that you get a fire going using combustible materials like wood or dried hedge trimmings and then throw lumps of clay on top of the fire.

This is not a complicated process and you can do it any time of the year. It does take a small amount of preparation and you can only expect to burn small, manageable amounts of clay in batches. This will depend on the amount of burnable wood or hedge trimmings that are available to you at any time.

You need to have a heap of clay lumps stored in a convenient place, ready and waiting for when you can get a fire going. Wait until the fire is going well then simply throw a few lumps of clay on top, ensuring that they are in the hottest part of the upper fire with flames all around it. As the fire begins to drop, load on some more wood on top of the burning clay to keep the fire going.

When the fire catches up with more added fuel, load on some more clay lumps. Then add some more fuel. This is a process that can go on and on until you either run out of fuel or clay.

This procedure is ideal for burning small amounts of clay. Doing this regularly will eventually change a significant volume of clay. Once it has been processed in this way the structure of the soil will be changed forever and it won’t revert to how it was.

The simplest way of burning clay soil lumps is to have an open fire in the garden but you could use an incinerator to get the same effect. This would be a much more controlled way of burning clay as the heat generated by the fire would be more contained rather than dispersing out and away from the fire.

The process would be just the same as an open fire. You need to have a stock of clay lumps ready and waiting for processing and a good supply of wood material as fuel. You then need to get the fire going really well before loading in a layer of clay lumps. Allow the fire to work on this, then place some more wood fuel on top of the clay. When the fire catches up to be hot enough, load in some more clay lumps as you would with the open fire.

When you’ve filled the incinerator, leave it to burn out and cool down. This part may take 2 to 3 days. Don’t try digging it out before it has cooled because you may burn yourself. When a mass of this type gets hot it can hold onto the heat for a few days so don’t be in too much of a hurry.

Whether you use the open fire technique or an incinerator you will be producing a product that can be spread on the garden. This would include the ash generated from the burning of wood or hedge trimmings. The ash will be high in potash which is all good for the garden as plants benefit from it.

How do you separate clay from dirt?

If you have dirt in your clay then the best thing you can do is to leave it where it is. Clay is a material that needs the addition of just about anything to improve it. Dirt in clay will help to keep it open allowing air and moisture to move through it. The question should really be: how do I add more dirt to clay? Rather than separating it from clay.

What plants grow well in clay soil?

Nothing grows well in clay soil. There are no plants for which it can be said ‘this needs clay soil’. Clay soil that hasn’t been managed in any way will become obvious to any experienced gardener. There will be plant growth but the performance will be clearly stunted. This will be due to a combination of factors including the familiar soil compaction that comes with solidified clay.

Plant roots struggle to make progress where there is compaction. There is also a problem where there is excess moisture. Clay soil doesn’t drain. If plant roots are trapped in water the plant becomes waterlogged and no air can get at them. This impedes plant growth with plants appearing weak and spindly.

The best you can do with clay soil is to grow just grass but whatever you grow, don’t have too many expectations. Clay soil needs remedial attention. If there is no intervention then the options are few and the output will always be limited.

What organic matter to add to clay soil?

The best organic matter that you can add to clay soil is compost. If you haven’t got enough of your own generated compost from kitchen waste, lawn mowings or dead leaves then consider importing ready-made compost from a supplier.

All types of soil will benefit from a generous application of fully converted compost. None more so than heavy clay soil but it isn’t critical that the organic matter is fully decomposed. If, for example, you are lucky enough to acquire a lorry load of wood-chip, this can make a big difference.

It would be wise to leave the load in a heap for a while. Even better if you dig it over and get some air into it to begin the rotting process. When it’s shown signs of have started to rot, then you could start spreading it on the clay soil. Don’t worry too much about mixing this into the soil. Organic matter will carry on decomposing on the surface.

The only downside to doing this is that when organic matter rots down, either on or mixed into any soil, the process will take nitrates from the soil. This can be remedied by replacing it with bagged, high nitrate fertilizer. This may be seen as a small price to pay when you consider the advantages of incorporating plenty of organic matter into clay soil.

Leaving this type of material on the surface may seem a lazy way of doing things but one big advantage of adding organic matter to heavy clay soil is that it will attract worms. Heavy clay soil tends to be hostile to worms. A layer of rotting wood-chip will change that. The best time to do this is over the winter when the ground is dormant. Organic matter will rot down in winter during periods when the ground isn’t frozen.

When there is enough organic matter available on the soil surface the worms will get into it and begin the process of tunneling into the soil, depositing the rotting wood-chip that they digest, beneath the soil surface. Over time you will see the whole consignment of whatever organic matter you’ve applied, disappear below ground.

How do you dig through clay?

As with any digging, if you do it by hand then it’s hard work but it could be argued that it’s good exercise. The thing is that, if you are doing it by hand, you must take care not to injure yourself. If you aren’t used to doing a lot of intense physical activity, and most of us aren’t, you must build up gradually. Do a little today then a little more tomorrow.

You can, however, use a mechanical rotovator. These do a good job very quickly and can be good fun. If you have much to do then this has to be the way to go.

Whichever way you do it there is something that you need to be aware of when you want to dig through clay soil. Do not attempt to dig through or rotovate clay soil when it’s wet or just damp. You may get away with it if you are digging through by hand be sure to look closely at the condition of the soil.

The worst thing you can do is use a rotovator on damp clay soil. If you do, expect the soil to become smeared. You will create lots of lumps which will be sealed. They will set when dry as hard as concrete and you will find it much more difficult to break them up and create a tilth.

Added to that there will be another problem which won’t be immediately obvious. As the rotovator moves through the soil the blades will smear the subsoil forming an almost watertight layer. You won’t see it but it will be there. This will impede water drainage which will bring more problems. Such a layer will also be impermeable to roots of plants which need to go down deep.

Clay soil that becomes smeared and compacted in this way can be rectified but it will take heavy, deep cultivating equipment which will have to be used in the right conditions. So the message is very simple, keep off it when it’s damp!

What grass grows well in clay soil?

Any of the grasses will grow in clay soil but none will perform well when comparing with other types of more open and free-draining soils. The thing with grass is that most varieties can survive with shallow roots and they aren’t troubled too much by the compaction that often happens with heavy clay soils. If you have an area of clay ground and you don’t feel like preparing it for growing vegetables that need to deep-root then grassing the area may be the best compromise.

If you have an area of grass growing on clay soil it’s wise to spread organic material, ideally compost, on the surface. This will do much to feed the shallow roots of the grass. It will also encourage worms to move in which will improve the structure of the soil. This may only happen in the top few  inches of soil but it will help the grass to thrive.

What is the average PH of clay soil?

It isn’t the average PH level that you should be thinking about. The neutral level on the PH scale is 7. Any measurement below this will mean acidity, anything above will mean alkalinity. By its nature heavy clay soil tends to be acidic with a PH below 7 which will vary from one location to another.

The question you should really be asking is: what should the PH level be for clay soil? The PH level of clay soil should be taken seriously if you hope to achieve any plant growth performance.

When you test the PH level of your soil, before you do anything to it, you may find that the level will be below 5. You need to take remedial action to get this level up to somewhere between 5.5 and 7. At this level, plants are able to make more use of the range of nutrients in the soil. It is also much more suitable for bacteria to function at these PH levels.

There is also an issue with clay soil containing a high level of aluminium. If the PH level is below 5 then this level of acidity can cause the aluminium to become toxic which would be detrimental to any plant life.

The best way to raise the PH level is to add hydrated lime. This will directly react with any acidity.  As a guide, if you have a starting point PH of 5 then you will need to spread approximately 18lb of hydrated lime per 100 square feet to get the PH level up to 6.5. Lime is often referred to as the ’soil sweetener’. You need to be ready to get some on the ground if you want to get good results.

Why is clay good to have in your soil?

When you compare the amount of work involved with managing clay soil to sandy loam soil the latter is the easy choice if you have the option. But if you feel that you are lumbered with heavy clay soil and that there are few, if any, advantages then think again.

Having some but not all clay in your soil does offer a few but valuable advantages. Because of the structure of clay it will hold on to everything that you need your soil to hold on to. Clay soil is not easily free-draining. When you water plants that are in clay soil the water will hang around for a lot longer than in free-draining sandy soil. This is of immense value in times of drought. Deep rooted plants in clay soil will thrive in a prolonged dry period of weather.

It’s important to be aware of this water retention potential because it’s possible to over water. You need to monitor the progress of plants that are receiving managed amounts of water. If the leaves on plants in clay soil look pale or have a yellow look, this may be because the roots are contained in an excess of water. Growing anything in clay soil does require a degree of management.

For the same reason as water retention, clay soil does have another advantage over free-draining sandy-soil. Any available nutrients in clay soil will remain in place for plant roots to absorb. In sandy-soil, nutrients will leach away before the roots can make full use of it. When applying any extra nutrient plant feed on clay soil there’s a much better chance for the plants to make full use of it.

Plants that establish a good root system in clay soil become well anchored in the ground. This means that they’re less likely to be pulled up or dislodged by trauma from strong wind or other attempts to physically stress them. Although for a root system to become established in heavy clay-soil, you must do all that you can to cultivate as deep as possible so that there is enough open soil for the roots to grow into.

What fertilizer is best for clay soil?

Any fertilizer will work on clay soil. There is an advantage when applying fertilizers to clay soil. The structure of clay soil tends to impede free-drainage. It holds on to whatever you feed in for much longer than any other soil type. So you don’t need to apply as much fertilizer on clay soil as for on sandy soil.

On clay soil you can apply granular fertilizers or liquid fertilizers with the expectation that it will stay around long enough for it to do some good. The same applies to organic fertilizers like compost or fish emulsion fertilizer. What is fish emulsion fertilizer?

Whatever soil type you have, be aware that as soon as any fertilizer hits the ground that there is a risk that it will go through the soil and head straight for the water-ways. These plant feeding fertilizers are extremely effective at promoting plant growth and in doing so pose no pollution threat but if an excessive application leads to run-off it can cause problems.

Considering this issue, clay soil has an advantage over free-draining sandy soil. Here you can’t win. Whether the fertilizer is on the surface or incorporated into the ground, heavy rain will dilute it and try to wash it away straight through the soil. Artificial fertilizers leaching into rivers and lakes is one of the biggest pollution problems that we have.  

It’s important to think ‘economy’. Clay soil will hold onto whatever fertilizer you apply but if you apply too much then some of it will wash from the soil surface if there is heavy rain.

The best way to avoid losing fertilizer as excess run-off, and wasting money while doing it, is to apply small amounts at any one time. This way the plants will be able to absorb it and convert it into plant-growth as fast as they can and there will be very little left to soak away.

Applying small amounts is better for the plants. If you over feed using artificial fertilizer plants tend to grow faster than is natural for them and they become, what is known as, ‘leggy’.  They become structurally weak making them susceptible to wind damage. It can also affect the plants natural immunity to a variety of diseases.

When applying fertilizer to any plants you need to monitor how the plants progress. If they appear to be growing too fast and becoming ‘leggy’ or they look under-grown and starved then you need to adjust accordingly. When it comes to feeding plants in clay soil with fertilizer, you have one of the few advantages that clay soil can offer.
Fish emulsion fertilizer

If you you aren’t too worried about the strong smell of rotting fish, this is, possibly, ideal for you. Early American settlers used to bury fish in the ground to feed the growing corn crop, so there’s nothing new about this. As organic fertilizers go this must be one of the best. Committed organic growers around the world who see chemical fertilizers as being toxic and harmful to the environment are using fish emulsion as an organic fertilizer.

What is a fish emulsion?

I must confess, I haven’t tried this, yet. Fish emulsion is, apparently, a mixture of fully decomposed fish mixed with sawdust and added molasses.

A successful compound of ingredients consist of one part fish, three parts sawdust and a bottle of non sulphurous molasses. Some water may need to be added to produce a fluid solution. These simple, although slightly pungent, ingredients can easily be assembled at home.

When you put these ingredients together the nutrient value is quite impressive. It can boast an NPK (Nitrogen: Phosphate:Potash) of 4:1:1.

This is ideal for a situation where growing plants show signs of needing a nitrate boost. A filtered solution of fish emulsion dissolved in water can be used in a sprayer as a foliar feed.

Making your own fish emulsion is cheaper and better than buying a commercially ready made brew. Depending on how much fish you can get hold of you can make a decent sized batch to keep in store. Making your own fish emulsion will also produce a much better quality product because when you do it yourself you will use whole fish.

The commercially produced fish emulsion will, most likely, be made up of odds and ends left over from being selectively cut up. This will mean the the commercial mix will be short of protein, oil and bones. Then we have to consider the available microorganisms in the mix which may be limited by the a sterile process.

Commercially produced fish emulsion is most likely going to be produced in near sterile conditions. This will mean less microorganisms in the mix where as your own mix will have the full deal with a strong presence of microorganisms.

You can help to make sure that there are plenty of microorganisms in the mix by throwing in a scoop of homemade compost. This will be teaming with a rich source of bacteria and fungi.

The process for making fish emulsion is easy. You need to find somewhere suitably far enough away from immediate habitation. You need a big bucket or container with a lid. Place in all the ingredients in the required proportions and stir it every day for about two weeks. Doing this will ensure that the fish break down completely producing one of the most wonderful delights that our bounteous nature can offer.

How to use fish emulsion

When you get to the point where you have a stock of this material you will be pleased to know that a little will go a long way. Fish emulsion needs to be diluted. One tablespoon of fish emulsion to be added to one gallon of water is enough to do wonders for spraying on foliage or for pouring around plants. After pouring around plants it’s wise to water the plants to help soak the emulsion into the ground.

What crops can be grown in clay soil?

Any crop can be grown in clay soil. The trick is to manage the soil in the best way to get the most from it. It takes skill and experience to get the best out of it. Only ever work clay soil when it is dry but not too dry and take whatever opportunity you can to work it as deep as possible to encourage good drainage.

As with any soil your target is to get a good tilth that is finely worked. This will be essential for the type of small seeds that you will be sowing in a vegetable garden.

Clay soil will always benefit from the addition of organic material. A well made compost and plenty of it will work wonders. It will also attract worms which will open up the structure of any soil. This will help with drainage and let air in that will aid root development.

Clay soil does take extra effort but if you work at it and with it you can expect to be rewarded.

Is peat moss good for clay soil?

Peat moss would do much to improve any clay soil. It will open up the structure and help to hold on to moisture which will make a difference in a drought period. It will also help to retain nutrients in the soil.

The downside is that peat moss tends to be acidic which means that you will be adding acidity to what is already an acidic type of soil. This may be what you want if you intend to grow acid loving plants.

Then there is the question of what is environmentally best. It’s understood that the harvesting of peat moss tends to release CO2 into the atmosphere.

Depending on which side of the debate you stand, you may not be comfortable with potentially adding to what some say is a problem.

Given a choice I would suggest using compost rather than using peat moss. Compost has much more value in terms of nutrients and it has an abundance of microbial life forms which will enhance any clay soil. It will also attract worms which is always a good thing. Peat moss, on the other hand tends to be a bit flat, doing not much more than adding organic fibre with little or no nutrient value.

What creates clay?

The clay soils that we are familiar with were generated over a very long period in geological time. As with most soil particles clay soil particles began as rock which were eroded down to become small particles. This would have happened by constant weathering, glacial friction or a combination of the two.

Clay particles have their own characteristics which literally separate them from other soil types. This is due, in part, to the range of minerals that can be found in clay. One of these is the included range of silicates. Most of us are familiar with silicone. When this is isolated it displays lubricating  properties.

The silicone in clay is one of the ingredients that makes clay so slippery when it becomes wet. It’s also a major contributor to the explanation of why we find clay where we do. You rarely find clay soil in large quantities at the tops of mountains or hills.

Because it‘s unstable it tends to find its way to the lowest point, typically in the bottom of a lake, or where there was once a lake. Here it has settled, where there is no flowing water, into layers which have built up over time. This has happened over a long period of time where weathering from rain has washed it down to the lowest point.

How much lime should be added to soil?

You can’t begin to answer this question without having carried out a soil test to establish the level of acidity. This will apply whatever soil you have but you can expect that there will certainly have to be lime added to clay soil. Unless it’s been treated before you took control of an area of clay soil you can assume it to be acidic to some extent.

Having tested your soil you will have a PH reading. The neutral PH reading for any soil is 7. The reading you will have will be below 7 and will probably be in the range of 5 to 6.5. So, then we can come to the question of how much lime to apply to correct the acidity.

If you just throw some lime around and guess at it you will do some good but there is a risk that you may add too much. So here’s a basic guide that will do enough for what you need in a small garden.

If we take as an example an area measuring 100 sq ft and we want to raise the PH level 1 point from 5.5 to 6.5 you will need to add lime at these rates:

  • Heavy clay soil – approximately 8lb
  • Loam soil – approximately 7lb
  • Sandy soil with some loam – approximately 5lb

Some say that if you are using finely ground limestone then expect the treatment to take longer to work than the much finer hydrated lime. In my experience, if you spread lime at the beginning of the growing season then the seeds that you sow, after spreading, will benefit almost immediately. The hydrated lime may work marginally quicker than the ground limestone but both will work fast enough for you.

Having spread your lime you won’t need to apply any more for 2 to 3 years. It is slow release over a long period and you will see the benefit of it over this time. It will be good practice to test your soil again after 2 years to see what is happening and get an idea of when to apply lime again.

What does clay soil feel like?

You will experience clay soil in two ways. There will be wet or damp clay soil or dry clay soil. Wet clay is what you shouldn’t touch. It will stick to your boots so much that you will struggle to get along. If you try to walk on wet clay soil you may have trouble standing because your feet will get stuck in it and, when trying to move around you will most certainly slip and fall down in it and get it on your cloths.

This won’t be too much of a problem because there are two approaches to cleaning off clay. The first is to wet wash. It will wash out quite easily. Or you can let it dry and brush it off. I’ve done both.

There is nothing to be gained in attempting to do anything with wet, or even damp clay soil. In trying do anything you will only damage the structure by smearing it, compacting it and generally making it harder to work when it eventually dries out.

Then there is the dry clay soil. This you can do things with but you must choose the right time to handle dry clay soil. Having mentioned the problems with wet clay soil you can have problems if it gets too dry. If this happens then it is likely to form lots of small but hard lumps that are very difficult to break up. This makes it difficult to achieve a fine tilth for sowing small seeds.

One way to get around this is to sprinkle some water all over these very dry lumps and leave it for 1 or 2 hours to soak in. This will ‘slacken off’ the lumps and make them workable. It will only take a small amount of water to do this. When you have done it a few times you will get a feel for it to know how much water to apply.

How can we improve the soil?

Whatever soil type you have there will be things you can do to improve it. Most of the improvements will be to do with drainage and generally maintaining an open soil structure. The addition of organic material from any source will make a positive difference. When you begin to manage an area of soil and notice, when digging, that there are no worms, then there is definitely scope for improvement.

One way of bringing worms to worm-empty soil is be adding organic material. This with the addition of lime that will reduce acidity, will create the a better habitat for worms. When they turn up, they will open up the soil and pull organic material down into the soil. They will change the structure of the soil just by living in it.

The best organic material will always be a well made compost but there are other sources. If you can gather plenty of leaves, they can either be converted to compost, which will take up to 2 years, or be spread as a mulch on bare soil. These will rot on the surface and will be taken in by the worms. The best time to organise this is during the winter months when the soil is dormant.

Improving soil isn’t too difficult to do. By the same token it’s easy to damage soil if you do any of the wrong things. The most important point of all is that you need to avoid trying to do anything to soil in wet weather. This is true for most soils and especially if there is an inclusion of clay. Any activity on heavy clay soil will lead to compaction. If you can do enough to avoid this then you will have soil that will deliver. Find out more about how to make compost, see: What goes in a compost bin.

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