Categories
BLOG

weeds in compost bin

Weeds in compost bin

We are often advised that as perennial weeds will survive home composting using cold composting techniques they should not be composted at home but put in the “Green” bin to be collected by the Council as part of their kerbside collections. This will mean that the weeds are hot composted by the council and then can be purchased back by the home gardener as part of commercially available composts.

However in most cases there are options available to the home composter faced with perennial weeds involving pre-treated so as to make them safe to be cold composted. These options include drowning, ( See Plant Liquid Feeds) desiccation and starvation/light deprivation for at least two years.

Before considering composting plants that may be toxic or invasive please check the advice on the Toxic Invasive Plant page.

Light deprivation

While normal cold composting, using a one year cycle, may not kill the roots of perennial weeds composting in a covered heap, from which the light is excluded. A period of two years has been reported as being effective for many perennial weeds. Turning the heap raises the temperature and will reduce the number surviving .

Charles Dowding https://charlesdowding.co.uk/advice-on-making-compost/ composts perennial weeds, including bindweed, docks, nettles, buttercups, dandelions and couch grass in a layered bin turned once. Weeds with soil on their roots can be included. The weeds will break down even in winter’s cooler heaps and regrow only if left exposed to light.

When I took on my first allotment plot it was covered in perennial weeds and I took the lazy approach of making a pallet bin using four pallets, filling it with weeds, turning it just once when the bin was full and leaving it, covered, until some of the pallets rotted. Although there were a few roots struggling to survive on the surface where some light had seeped in, the compost was excellent.

When using this and any other method of treatment on this page it is recommended to check the compost at the end of the treatment to ensure the absence of living roots before use.

ASK Organic (http://askorganic.co.uk/composting/perennial%20weeds.pdf) recommend using a separate plastic compost bin so as to ensure that all light is excluded which may not be possible if using a wooden bin. The material is kept covered in the bin for two complete years to rot down.

Where perennial weeds are growing in turf or grass which must be cleared, as may be the case when taking on a new or neglected plot, a turf stack can be used. The turves should be lifted and neatly stacked green sides together. The stack is then covered by a black plastic sheet and left for up to two years by which time they will have rotted down to form a quality topsoil. This method can be used successfully to deal with couch grass.

Bagging perennial weeds

An effective variation involving light exclusion is recommend by Alys Fowler

The weeds are bagged using biodegradable bin bags and stored for two to three years. The bags are covered with black plastic to exclude light and air and allowed to degrade. By the time the bags have degraded rich compost should be produced. One of the advantages of using biodegradable bags is that as the bags degraded worms gain access to the material assisting the composting process. Again the finished compost should be checked to ensure rots have not survived.

We are often advised that as perennial weeds will survive home composting using cold composting techniques they should not be composted at home but put in the “Green” bin to be collected by the Council as part of their kerbside collections. This will mean that the weeds are hot composted by the cou…

Composting Weeds in the HOTBIN

Can I Compost Weeds in the HOTBIN?

Yes. Even pesky perennial weeds can be composted in a HOTBIN. Here are the precautions and considerations to take into account.

What is a Weed?

Technically a weed can be anything in your garden that is growing in the ‘wrong place’. Do bear in mind though that one mans junk is another mans treasure and it’s the same for weeds. What one person thinks is a weed can be a precious flower to another.

Those weeds we don’t want can usually be characterised as such because they are pinching space, light and food from those plants we want to keep. A familiar site in domestic gardens as they pop up between flagstones; they are even more of an issue on allotments.

Types of Weeds

Weeds can be annual, biennial or perennial. The latter being the most problematic from dandelion, buttercup, nettles, docks and thistles to invasive types such as couch grass, bindweed/convolvulus, horsetail and ground elder.

Horsetail or Mare’s Tail (Equisetum Arvense) is an invasive, deep-rooted perennial weed which forms dense carpets of foliage forcing out less vigorous plants in beds and borders.

Easily recognised by its upright, fir tree-like shoots that appear in summer, Horsetail has light brown stems in the Spring which appear with a cone-like spore producing structure. In summer, sterile green shoots develop into fir tree-like plants.

Horsetail is an invasive and tough weed where rhizomes bury deep below the surface allowing them to enter other gardens beneath the surface. So if you are planning to compost this plant you need to check that the seeds/bits are only added to the top of an already hot pile (above 40°c). DO NOT fork in or turn the contents of the HOTBIN as seeds will fall down to cooler base.

Composting a weed – The Importance of Destroying Seeds and Rhizomes

Can I compost weeds?

As far as composting goes, weeds aren’t any more difficult to compost than other plants so they shouldn’t be wasted. If you are following general weed advice and removing them whilst they are young, the weeds will breakdown and make excellent compost quickly.

So why do some people not want to compost them?

The main complication surrounding composting weeds is to do with the seeds and the rhizomes, both of which can cause chaos if not destroyed effectively.

Proving to be problematic seeds can survive in soil and cold compost heaps laying dormant for many years. This can include seeds from melons and tomatoes plus weeds like couch grass and dandelion which when left in a cold compost heap are planted in nature’s best growing medium – humus/compost.

If they are not destroyed properly the weeds can end up being spread over flower and vegetable beds in final compost causing mayhem to your plot.

Rhizomes are a feature of perennial weeds, similar to strawberry stolons, however the rhizome represents the main plant stem, whereas stolons are “off shoots” from an existing stem. Rhizomes are subterranean roots; growing underground helps the weed survive through the winter and is responsible for the aggressive nature at which they spread. To destroy them you need to do more than cut them back to ground level, the roots need to be thoroughly dug out.

We Recommend

  • Reading up on weeds and make sure you don’t have any in your garden that require specific care. For example Japanese Knotweed which is a controlled weed species is particularly troublesome; we recommend following detailed advice for controlling it.
  • Catch weeds early before they go to seed and remove all rhizomes/roots.
  • Add to a self-insulating compost pile – the HOTBIN compost bin. Sustained heat of 40°C+ is required to kill weeds and seeds.
  • After hot composting invasive weeds like Horsetail you may wish to give your compost a germination test. Leave the compost in an open maturation pile for a few months to check there is no re-sprout – f it does, gently tease out all roots and rhizomes again and zap it through the hot compost again.

Do I need to destroy the weeds before adding to the HOTBIN?

Some sites advise destroying the weeds before adding to compost bins. Heat is the successful factor in the successful destruction of weeds and seeds if you want to compost them. Even the peskiest perennial weed cannot survive sustained hot composting temperatures of 60°c.

Advice | Destroying Weeds Through Sustained Heat in the HOTBIN

  1. Ensure you are HOT composting between 40-60°c. Never add seeds to a HOTBIN that’s not up to temperature, otherwise seeds will be spread in final compost.
  2. Add weeds and seed heads into the top of the bin, the hottest part and place in the middle – do not fork the mix in as they could then fall to the cooler layers or down the sides and may survive.

What About Weed Killer?

Domestic weed killers are biodegradable so adding grass or weeds with weed killer on shouldn’t be a problem, however please check individual product instructions.

Test Your Final Compost

To reassure yourself that the weeds are gone especially with invasive ones you may decide to do a test. Simply plant up some small pots with your final compost and water to see if anything germinates, if not, hot composting has successfully destroyed them.

Bear in mind that at the end of the day it’s difficult to get rid of all weed seeds – birds will kindly drop them, the wind will carry them and they can even lay dormant in the soil for years… and then there are the rhizomes!

Compost various weeds from dandelions and buttercups to horsetail and ground elder in the HOTBIN. Just make sure you are hot composting first to ensure the weed seeds are killed off.