Can you use weeds for compost?

Go to Home Page

One thing that you can be sure of if you have a garden is that there will always be a plentiful supply of weeds. Having pulled them up and cleared the infested area, you now have a load of weed plants which you don’t want. You don’t want them to take root again. For them it has to be the end. So, how can you fully dispose of them? Can you use weeds for compost?

You can use weeds for compost. Weeds will rot down just like any green material and turn into compost. The best time to put weeds in compost is when they are young, before they go to seed. Weeds that are carrying seeds can go in compost but there’s a risk that some of the seeds may survive the composting process.

Weeds will rot down just like grass clippings from the lawn. If you’ve been putting weeds in the trash can to be taken away, don’t. A good composting system will easily cope with a load of weeds in the same way as any other green garden trimmings.

Weeds will not survive in a compost heap. They will break down with everything else. You won’t be able to identify weeds when you take out the compost to use. There is no possibility that weeds will regenerate when spreading compost that includes weeds. The roots will rot down along with the rest of the plant.

The biggest problem with weeds is the seeds. If you pull them before they go to seed then this won’t be a problem. If the seeds haven’t formed, then there won’t be anything that can germinate.

Weed seeds that get hot in compost won’t grow

You will only have a problem with weed seeds if you are pulling weeds that have gone to seed, from around mid Summer to late Autumn. These will be full of seeds. You can put weeds that are loaded with seeds in the compost bin, they will rot down but to be sure of destroying the seeds there needs to be heat.

A compost bin that contains a balance of fibrous vegetable material is likely to become hot as it goes through the early stages of composting. The problem will be that only the middle of the mass of compost in the bin will become hot enough to destroy the seeds.

Weed seeds tend to sprout in the compost

The cooler areas in the compost will rot down but the seeds from weeds are likely to survive. This is when you may see some weed seeds germinate in the compost bin or they may survive and come through to be spread with the finished compost. This doesn’t have to be a problem. There are simple ways of suppressing weed seeds and any other rogue seeds that may be around in the compost.

The young weed plants will be very delicate. If you throw fresh waste into the compost bin, the action of doing this will crush and generally damage these seedlings. They will be easily damaged, enough to stop them from growing any further and they will break down to become compost.

A tumbler composter tends to kill sprouted seeds in the compost

This can also happen in a tumbler style composter. Seeds of all types tend to germinate in the Rolypig composter. They will grow two or three inches in height. The next time the barrel of the Rolypig is rolled over 360degs, these tender shoots will be crushed under the mass of all the compost in the barrel. They are then killed by this action and become part of the compost.

If you aren’t impressed with doing things this way and you want a more decisive way of rendering weed seeds inactive before they go in with the compost, there’s something called ‘weed soup’.

Can you use weeds for compost? Yes. Weeds will rot easily.

Drown the weeds and seeds

Basically, what you would be doing here, is drowning the weeds and seeds. This is a decisive way of getting rid of pulled weeds, both annual weeds and perennial. You need a big bucket or water-tight container. You then load in the weeds that you’ve pulled.

Next, fill the container with water, enough to fully submerge the weeds. Place a heavy, flat stone on top of the weeds to keep them below the water-line. The container must be covered to stop extra rain-water from over filling the water.

This needs to be left for four to six weeks. After this time the total saturation of the weeds and seeds will render them all completely useless. The vegetation material can be taken out and put in the compost bin, heap or pile.

The remaining liquid has a use. It can be used as a liquid fertilizer. It tends to be a bit concentrated. So, you need to dilute it. Adding 4 parts water to 1 part of the saved liquid should give you solution that will do more good than evil.

Dry weeds can’t grow

This will stop the roots of weed plants from regrowing. Drying won’t do any good if the weeds have seeds on them. Drying is what seeds need to survive.

You need an area of floor-space that catches the sun. A concrete path or somewhere similar would be ideal. You also need a few days of scorching sun shine.

Spread the weeds out on the floor surface and just leave them. After a few days of drying, the weed plants will have turned to ‘hay’ and, more importantly, the roots of the plants will have become limp and rubbery. Leave them for a day or two longer and the roots will become baked dry. When they get to this stage, they won’t regrow. It will now be safe to put them in the compost bin.

Hide weeds in a bag

If you have so many weeds that your compost bin can’t cope with them all, put them in plastic bags. Tie off the tops and hide them somewhere behind the garden shed. Leave them there for a couple of years. This will give them long enough to rot down into compost in their own time.

You may want to make holes in the plastic bags but this may not be necessary. Air always seems to be able to find its way in and we’re going to be leaving it for a very long time.

Think about Bokashi

The bokashi system is all about fermentation. It starts with adding a bran material that’s been inoculated with specially selected microbes that become active and multiply when they become moist and are in the presence of material that they can feed on.

Any organic material will break down in the bokashi system, including weeds and their seeds. If you have a bokashi bucket already working for you, for kitchen waste, then you can put weeds in it but there may not be room for many.

It may be worth setting up a seperate bokashi bucket just for weeds. Find a suitably large bucket, preferably with a lid. Make a layer of weeds in the bottom of the bucket, about one inch. Don’t worry about cleaning off the roots. Sprinkle about a tablespoon of bokashi-bran onto the layer. Add another layer of weeds, then more bokashi. Build the whole thing up in layers.

When you’ve got all the weeds in the bucket, press them down to achieve good surface contact of the bokashi bran on the weeds. You can get a lot of weeds into a small space.

Put the lid on the bucket, this process works best when the bucket is sealed. Leave the contents of the bucket to ferment for at least a month. By this time everything should have broken down completely.

The bokashi process generates a very acidic mass of material. The weed plants will break down and any seeds will be rendered useless having been soaked in acids.

This is not the same as composting. Acids are generated in compost making but nothing like as aggressive as that in the bokashi process. When the bokashi fermentation process is complete, the fermented mass can be placed in the compost bin, heap or pile. This requires an extra consideration. Because of the high level of acidity from the bokashi treated material, we now have an increased acidity level on the compost heap.

Acidity preserves, we want decomposition.The best way to reduce acidity on a compost heap is to add hydrated white lime. It will take more than just a sprinkling of lime to tame the acidity of bokashi fermented waste. To save the compost from a sudden influx of highly acidic material, it may be better if the fermented bokashi material is treated with lime before adding it to the compost.

You will know when you’ve added enough lime to the bokashi waste because there will be noticeable signs of decomposition.

Some people dig a trench in the vegetable garden and bury bokashi-fermented waste. This will work. It will save all the fuss of stressing the compost in the bin with the extra acidity. However, it’s still advisable to sprinkle a liberal amount of hydrated white lime on top of the waste before backfilling.

Don’t forget the bokashi liquid

The liquid that accumulates in the bokashi bucket has a value. Collect it if you can. It can be used as a fertilizer but you must dilute it. Add 100 parts water to 1 part bokashi liquid, remember, it’s very acidic. You can also use it, in the undiluted form, as a weed killer.

Related questions

Will vinegar kill weeds?

Vinegar can be used as a weed killer. It is effective at killing every small weed plant that comes into contact with it. You don’t need to seek out a particularly strong, concentrated vinegar. Basic vinegar that you dribble over chips will work.

Vinegar will leave no residual effect that will carry-over, in the soil, and kill off any emerging weeds. There are no residual chemicals that may be seen as harmful to people, wildlife and the environment generally. It will kill what is there in front of you at that moment in time. Leave it for a while and there will be regrowth of weeds.

There is a story going around that if you add table salt to the vinegar, this combination will kill the weed plant to the root tips and no regrowth will appear. This is basically what ‘Roundup’ will do.

I haven’t seen the salt and vinegar mix being used and,therefore, have no data to show whether this works. I can only suggest that if there is no regrowth after the application of salt, it’s due to the salt contaminating the soil. If this is the case then nothing will grow in that particular piece of soil whether it’s weeds or anything else.

Applying salt to soil is a risky strategy. You can have strong views about the use of over-the-counter sprays for weeds but you need to know what you’re doing if you start mixing up your own remedies for killing weeds.

Do I need to pull weeds after Roundup?

If we’re asking here, do we need to pull weeds after applying Roundup to them, then the answer is no. Roundup takes about two weeks to work after the application. Apply the Roundup at the recommended concentration. Do it when the weather is dry but not too hot. Then, walk away and forget about it for a couple of weeks. The weeds will die and will be killed down to the root tips.

Will burying weeds kill them?

Burying of weeds will kill them. This is one of the reasons why farmers plough land. The weeds and any other unwanted vegetation, e.g. regrowth from a previous crop, will be underground after ploughing. They will not be able to regenerate from that position. The soil will be cleansed of weeds but this will only be temporary. Weed seeds that are in the soil, and may have been for years, will come to the surface when ploughed up. These seeds will be eager to germinate and the battle against weeds will continue.

Can I spray weeds before rain?

When applying any weed killer solution, the concentration has to be strong enough to do the job but not so strong that you’re wasting the chemical. With the concentration being where it has to be, it’s important that it doesn’t become diluted when it’s on the surface of the foliage that we are trying to kill.

So, when we are planning to spray an area of weeds, we need to watch the weather forecast. If it looks like there’s rain coming, then leave it because rain will dilute the application. If the rain is heavy and the application was applied just an hour before, then there’s a risk that the whole amount of spray will be washed off.

You need a dry, settled period of weather when planning to spray weeds. Allow for one full dry day after spraying to give the chemical a chance to work efficiently.

Go to Home Page