In the second of our series on caring for your soil’s health Alys Fowler looks at mulches and foliar feeds
The soil food web loves summer; the community buzzes with all the potential, the soil is warm so the microbes and the worms can work fast, the plants above ground are in full swing and releasing plenty of root exudates to influence the microbes around them.
The plants also insulate the soil, their leafy cover helps to protect against beating UV rays easily destroying soil-dwelling microbes. The leaves also slow down evaporation on hot days and physically protect soil from summer storms. All this helps to keep the soil in its prime and in return this means good, steady growth.
If you can keep your soil food web happy many of the most common gardening tasks, such as watering, feeding and keeping pest and diseases at bay, are done for you. The best way to keep the soil food web active is year-round plant growth. However, adding composts, organic mulches and various foliar feeds can be used to both restore soils lacking in a healthy soil food web and keep fertility active. Although spring and autumn are the traditional months for adding compost and mulches, a little judicious application now can be just as useful. Additionally foliar feeds throughout the growing season can do wonders for plants, helping to address deficiency, giving plants a quick pick-me-up and preventing diseases.
Summer mulches and top ups
Home-made compost and organic mulches will feed the soil, lock in moisture and prevent evaporation on hotter days. Just like plant growth, mulches will physically protect the soil. Mulches insulate, keeping the soil cooler in summer. As both compost and mulches break down they encourage earthworm activity, as the worms take this source of food down into their burrows. This in turn opens up the soil structure, allowing water to move through the soil more freely, which helps if there are summer floods.
The golden rule for spreading either compost or mulch is to realise that you maintain the existing conditions of the soil at the point of adding the top material. If you mulch when the soil is warm and moist it will remain that way; mulch when the soil is very dry or very wet and you’ll just lock in the problem in.
Summer mulches tend to work best for larger, hungrier crops rather than for seedlings or salad crops. This is because any sort of organic mulch, particularly if it’s rough or semi-rotten, can encourage slugs and you need your plants to be large enough to defend themselves. Where mulches come in useful is for top dressing potatoes (particularly useful if you practise no-dig as it eliminates the need for earthing up), around crops that need to put on a huge amount of growth in a short time, such as courgettes, summer and winter squashes, corn, climbing beans and peas, outdoor tomatoes and cucumbers, and to resource hungry crops such as onions and garlic.
A good alternative for vegetables is fresh grass clippings or freshly cut comfrey leaves, both should be allowed to slightly dry and wilt out for a day or two before being added because very fresh leaves can compact considerably if added thickly and mulches need to be loose enough to allow for the free movement of air and water to penetrate through to the soil below.
Mineralised straw, such as the organic brand Strulch, semicomposted bracken and straw also make excellent summer mulches, helping to keep crops clean from soil splash back and conserving moisture. Straw is really best for very dry, free-draining soil, on heavier, clay soils, it does tend to become a bit of slug magnet.
Mulches work particularly well in conjunction with a thin layer of compost. Put the compost down first and then cover with the mulch.
The microbes in the compost will inoculate both the soil as well as the mulch, helping it to decay and release its nutrients.
Foliar feeds
There are times, however, when you will need to feed the plants directly rather than the soil. This is particularly true of containeror pot-grown plants. There are two ways you can feed: as a soil drench or as foliar feed. Plants take up nutrients far more rapidly through their leaf surface (a matter of minutes) than through their roots and the soil (can take several days). A foliar feed can be a direct injection of energy, compounds and necessary nutrients for an ailing plant or one showing the beginning signs of stress.
The plant’s leaf surface also has its own microbial community; there are many fungi and bacteria that live only on plant leaves and the right feed can also help to boost the good guys in this community (as opposed to the less desirable ones such as mildews).
Foliar feeds should be applied during the growing season; depending on the feed they can be used weekly, fortnightly or once a month. They should be applied early morning or early evening, out of direct sunlight. Foliar feeds need to cover roughly 70 per cent of the leaf surface to be effective, ideally both sides of the leaves. Any foliar feed can also be used as a soil drench as part of the feeding regime.
Foliar ferments
Foliar ferments are traditionally made from comfrey or nettles rotted down in water into a liquid feed. Other options for foliar ferments include dandelions (rich in minerals, such as calcium and magnesium, and nutrients, such as potassium), mares’ tail (rich in chlorine, calcium, magnesium and potassium) and chickweed (rich in phosphorous and potassium). Add your plant material to a bucket (around three-quarters full) and cover with water (ideally rain water).
After two to three days this can be strained and diluted at a ratio of 1:10 and used as a soil biological inoculant (similar to activated compost tea). After a week the pH drops, the material can be strained the liquid stored or you can let if further decompose (this is when it gets smelly) indefinitely. Strain and use at a ratio of 1:10 (roughly diluted to the colour of weak tea).
You can make aerated or activated compost tea using a compost tea brewer with an aerator (often an aquarium pump). This actively pumps oxygen into a mixture of compost and water to create a concentrate of aerobic microbes that are beneficial for the soil food web. You can use it on both the soil and leaf surfaces.
Another alternative is a fermented plant juice. For this you can use either leafy material or fruit (bruised tomatoes work well). Mix your plant material (either leaves or fruit, but not both) with organic brown sugar (roughly three parts plant material to two parts sugar or 1:1 with fruit) in a glass jar and cover the top with more sugar.
Weigh down the material with a stone or glass of water to initiate fermentation. Cover with a cloth, ferment for a week or more out of direct sunlight until you have a liquid. Strain the liquid and store in a jar with a tight lid. Dilute to a ratio of 1:500 and as a foliar spray.
Mineral extracts
You can also extract broad spectrum minerals, such as calcium and other compounds, from cooked bones, egg shells and shell fish. Cook the bones and shells at 150ºC for around an hour to extract water. Fill a glass jar with around 10-15 per cent mineral material and 85-90 per cent raw cider vinegar. Cover with a lid and watch it fizz, after a week decant and repeat until no reaction occurs. Dilute at a ratio of 1:500 (roughly one tablespoon to 15 litres of water) and use a foliar spray.
You’ll find additional recipes in the books listed below.
FURTHER READING
The Regenerative Grower’s Guide to Garden Amendments by Nigel Palmer (Chelsea Green Publishing, 2020).
Compost Teas for the Organic Grower by Eric Fisher (Permanent Publications, 2019).
LOOK OUT FOR PART THREE OF THE SERIES IN THE SEPTEMBER ISSUE: Protecting and harnessing soils over winter.
How to mulch
Mulch is anything that can be put on the surface of the soil to slow down evaporation, prevent weeds and insulate plants. It is much better for the soil food web if the mulch is organic, rather than say a plastic weed-suppressing membrane, because it will break down and feed the soil rather than pollute it. Many things make good mulch: leaves, leaf mould, grass clippings, pine needles, bark and wood clippings, seaweed, rough or semi-rotted compost, shredded paper and/or spent compost (such as last year’s tomato compost from pots).
WHAT TO DO NOW
Mulch around larger vegetables and other plants to help conserve water, insulate and improve soil structure. Ideal for potatoes, chards, rhubarb and squashes.
Grass clipping mulches will aid bacteria in the soil and are excellent for the brassicas.
Leaf mould mulch will work better for fruit bushes and strawberries.
Container-grown plants will need feeding every seven to ten days: use either a soil drench or a foliar feed.
On the whole plants grown in the soil shouldn’t need supplementary liquid feeding, unless they are ailing for some reason. If you do need to feed, try a pick-me-up of seaweed or fermented plant juice.
