Fewer weeds in no dig

Whenever soil is dug, loosened or turned over, it recovers from the disruption by re-covering with weed growth – both from roots of perennials and seeds of annuals.  By contrast when left uncultivated it has less need to re-cover and therefore grows less weeds, as shown by a look at Homeacres at any time of year.

There are always a few new weeds,  from seeds blowing in or brought in with composts, and they need removing by hand when small, or hoeing off as tiny seedlings. It is a little and often approach. Vegetable growing is bountiful and easier when weeding is just a small issue, small but still important. 

Mulching to clear soil of weeds in polytunnels is the same story, see my early posts of 2013 for how I mulched a tunnel of weeds, starting here and scroll down halfway. See Ferryman Polytunnels for some ideas of structures and prices, and my article on this site.

Clearing weeds

The first step depends on how many and which weeds you have (especially perennials) and how much organic matter you can use.  The mulch(es) you lay are to clean soil of weeds by a smothering, light-deprivation effect. Mulches of organic matter also feed soil and its inhabitants.

There is no need to dig before starting, or to incorporate manure at depth. Placing organic matter on top is the best way to bring soil alive because that is how soil organisms work, searching for and eating organic matter at the surface, then digesting and excreting in the soil, building a permanent structure in so doing. Incidentally, worms love working under black polythene, if you are using that initially.

In damp climates such as the UK, I recommend not using mulches of undecomposed organic matter, such as straw, which allow slugs to hide by day and eat your plants by night. Where slugs are potentially prevalent, compost is the mulch of choice because it does not harbour slugs. Composted beds look ‘bare’ when not growing vegetables, but the compost mulch is protecting soil below.

The time needed between mulching and sowing can be instant (see online course)  if you have enough compost, say a 6in (15cm) layer (option 2 below), otherwise within 6-12 months as in option 1, depending on the current perennial-weed situation, and whether the timing works for vegetables such as squash and potatoes. 

Some weeds that need digging out initially

Docks and woody plants such as brambles are best removed with a sharp spade, before mulching. Otherwise they push mulches up and reach light before they die. Use a sharp spade to cut around bramble clumps, removing the main crown but leaving all small roots in the soil. For docks, remove the top 6in (15cm) and then they do not regrow; I put these roots on my compost heap and they break down nicely.

Wooden sides?

Its often assumed that growing in beds means you need permanent sides, but this is untrue, though they are sometimes useful, for example in the first 6-12 months of option 2. Temporary sides (such as old fence posts) help to keep compost-filled beds in shape, for the first few months, as in the first photo of option 2 below, February 2013, I then lifted off the unfixed wooden sides in early autumn of that year, once the beds’ compost had settled and path weeds were dead – this had needed a further laying of cardboard in May, and again in July for a few places with couch grass.

It’s quicker and cheaper to create open-sided beds, and they offer less hiding places for slugs and woodlice. However, you must have weed-free paths for this to work and absolutely no grass, which otherwise invades beds with no sides. This is why I used cardboard on paths in the first few months at Homeacres, to kill buttercups, dandelion and some couch grass. After six months or so, once those weeds had died from lack of light and the cardboard had mostly decomposed in situ, I spread some organic matter as surface mulch: half-rotted leaves, old straw, green waste compost and decomposing woody material are suitable. Then I treat paths like the beds, they receive a little compost from birds kicking it off the beds (looking for worms), and I weed where necessary, to keep them immaculate.

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OPTION 1 Some organic matter and polythene mulches

See the video for more on this

When significant perennial weed roots are present and you are using say 1-2in (3-5cm) compost, there are still possibilities for growing veg in the first summer. Occasionally, slugs may make this tricky.

1) Initial soil feeding and  mulching of weedy  plots

No Dig Growing Basics

Experimenting with different surface mulches on soil with couch grass, buttercups and cow parsley.

Any organic matter can be applied on top, for soil food and to increase the light deprivation of weeds below. Animal manures partly decomposed, composts of any kind, leaves and grass clippings are good for feeding worms which get busy under dark mulches. Soil is improving at the same time as weeds are dying off. The surface mulch of polythene, cardboard or paper is applied on top of the organic matter.

This option is particularly worthwhile if you are clearing weeds in summer or autumn, to have ground clean for the following spring. Or if you want to grow say potatoes and/or winter squash – see the photos below from Homeacres in 2016, taking a harvest of Crown Prince winter squash from ground that in April was 100% weeds, grass and some bindweed too.

2) Next step depends on compost depth and weeds

Before removing polythene or membrane, allow enough time for weed roots to be exhausted under whatever mulch has been used. Annuals need two to three months, many perennials take from six months or sometimes longer, for their roots to be exhausted by trying to grow in darkness. If you peel back a mulch and still find white stems of weeds, their roots are still alive, as in the last photo of the four above. At least in this case, there was not a lot of bindweed and we used a trowel to remove those shoots, to further weaken the parent roots below.

At Homeacres, on pasture full of perennial weeds, I remove polythene mulches after one growing season, say February to October at most.

Carpet applied to weedy pasture three months earlier, with 1in (3cm) old horse manure. Bindweed  Convolvulus arvensis is still growing white stems and leaves. White because they cannot photosynthesise, therefore the parent root is weakening all the time.

Carpet applied to weedy pasture three months earlier, with 1in (3cm) old horse manure. Bindweed Convolvulus arvensis is still growing white stems and leaves. White because they cannot photosynthesise, therefore the parent root is weakening all the time.

3) Normal Growing

After polythene/cardboard/membranes have done their job, you have a clean surface to sow and grow, which is the dark surface layer of compost you applied earlier, or apply afterwards. Seeds germinate and plants grow initially in the surface compost, then root into undisturbed soil below, which is firm but not compacted.  Firm is good!

Incidentally,  in dry weather soil becomes hard: this is normal and don’t worry, it softens with rain or watering. 

Some perennial weed roots may still be sending up new leaves, as happened with the bindweed after my carpet mulch. In this case you need to keep removing the regrowth, as often as possible, to weaken the parent root even more. By year three, even bindweed is rare and easily manageable.

OPTION 2 using 4-6in (10-15cm) compost to create beds

 When you have enough compost to create beds with up to six inches (15cm) on top of  weeds, this is sufficient to prevent re-growth of weeds, except you have extreme amounts of bindweed, marestail and dense couch grass – in which case, use option 1 above.

Six inches of compost, well trodden down, is  enough to kill annual  grasses and weeds, and to weaken if not kill perennial weeds such as buttercup, dandelion, and smaller amounts of couch grass. Over the next few months, use a trowel to remove any regrowth of perennial weeds , until parent roots are dead.

  • Cardboard option: In the photos I am filling  beds with well wheelbarrow loads of composted (two year old) cow and horse manure, homemade compost, and some green waste compost for the top inch or two. In the image above, I had only enough cardboard for the paths and to go under the temporary sides. Cardboard laid over the bed weeds as well, before compost, would have slowed regrowth of buttercups, thistles etc, of which a few pushed through the compost and I needed to pull them in spring, until the parent roots expired.
  • In the image below, half the bed had cardboard under the compost, half did not and in this case it made little difference to weed regrowth, because the perennial weeds were not too vigorous, having been regularly mown for three years previously. If there are vigorous perennial weeds, a cardboard layer is worthwhile – thick cardboard is best, or two layers of thin cardboard.
Filling a new bed on grass, one half with cardboard: the six inches of organic matter in this bed was enough to kill grass, dandelions and buttercups

Filling a new bed on grass, one half with cardboard: the six inches of organic matter in this bed was enough to kill grass, dandelions and buttercups

For an approach like this and to grow potatoes at the same time, see Naomi Schillinger’s blog of summer 2012.

Vegetables are hungry plants and require a soil that is well structured and full of life. First year dressings of organic matter may seem a lot but will repay the effort for years to come. Until the advent of chemical fertilisers, larger amounts of compost and manure were always used for vegetable growing. Since 1945 especially, more emphasis has been placed on chemical nutrients from synthetic or concentrated sources, but these fertilisers cannot provide soils with food for all its myriad of inhabitants who are so necessary in growing healthy plants. And some of their nutrients leach away in rainfall, which is both a waste and a pollution.

These parsnips were sown in well decomposed manure on top of heavy clay soil

These parsnips were sown in well decomposed manure on top of heavy clay soil

At Lower Farm my soil was clay below and I found that all vegetables rooted into it. At Homeacres my soil is dense silt and everything roots into that too. In my first garden 35 years ago, soil was Cotswold brash, very stony, and no dig was successful there as well. 

Undisturbed soil develops and maintains a honeycomb structure of small air passages, especially when it is fed annually with an inch or so of compost on top. This compost can be animal manure that has been stacked for six months or more, your own compost, municipal or mushroom compost, leaf mould etc

  • Wood chips A variation  is to apply 6-12in (15-30cm) of wood chips, and/or bark and/or shavings, to kill off weeds. If you have access to these materials for free, its worth considering.
    But the downside is a wait of up to two years before the lower layers have turned to compost, by which time you can plant (easier than sow) into that lower layer, with the surface wood continuing as weed-suppressing mulch and eventual soil food. Lots of wood mulch encourages woodlice and they nibble leaves such as spinach and cucumber.

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No dig ongoing

The surface layer

Sowing small seeds into large lumps of compost and manure is unlikely to succeed, so keep the most crumbly and finest  organic matter for your surface layer of mulch.

Likewise, an excellent time to spread compost is in autumn, as soon as the previous crops finish. Then there is time for frost to break up any lumps and for worms to start taking it down, leaving a fair tilth by spring. It also helps, when the surface organic matter is lumpy, if you knock it around in February or March with a fork, just on the surface, to smooth out the lumpy bits. 

Whenever you are spreading an inch or two of compost as surface mulch, break up any larger lumps, aim for golf-ball size as the largest, then weather can do the rest. I find that carrot and parsnip seeds germinate readily when sown into reasonably fine compost, then make straight roots down into the undisturbed soil below.

Maintaining abundant growth and few weeds

For vegetables, including for two crops in one year, average amounts of compost used annually are one to two inches on beds. Using less compost is possible but creates more work proportionate to results, through weeds growing, less healthy growth and smaller harvests.

For paths, you can spread an inch or two of wood shavings or sawdust, or leaves, straw, bark or less rotted manure. When growing without sides, the crops in beds root happily into weed-free, mulched paths in search of food and moisture. A caveat to this is areas with slugs, where path mulches should be more decomposed, to afford less habitat for molluscs.

Spreading compost in May after clearing winter cauliflower

Spreading compost in May after clearing winter cauliflower

Organic matter can be spread at any time of year. 
The most practical season is autumn, when soil is moist and still warm, so that worms can access it, and when harvests are finishing and soil is cleared of crop remains. Also, some ground becomes clear in spring after winter leeks, cabbages and so forth, and can be composted then if there is no remaining organic matter on the surface. Or you can spread compost in winter between leeks and broccoli.

I find that one composting a year is sufficient for two crops, once soil is in good heart. You can tell this by how healthy and vibrant your vegetables are looking.

Where to find the organic matter you need? Compost is becoming more available, and often cheaper, thanks to recycling of green waste, and there are surplus quantities of animal manure to be found in many localities, in addition to any compost you can make.

Animal manures

All are suitable, at least a year old, preferably dark in colour, with any lumps that can be broken up by forking through before spreading.

BEST AVOID horse manure that has a lot of wood shavings, because they take years to decompose and pull nutrients away from plants while they rot.

Horse manure is also at risk of contamination by aminopyralid weedkiller which is occasionally sprayed on grass for horse-hay. Its the only weedkiller I know which persists, and its lethal to potatoes, tomatoes and legumes, whose growing tips become curled and twisted, see here and elsewhere on this site via the search bar, and elsewhere.