Understanding How Leaves Work as Gardening Fertilizers
Leaves are Natural Gardening Fertilizers – Their Storage and Use
I am very much a leaf mould man. And in most gardens there are always some leaves available. There is food for plants in all decaying leaves which vary more in texture than in nutriment, although there is probably more calcium in those of horse chestnut than any others.
The value perhaps lies more in the texture. It is often stated in articles and encyclopedias that oak and beech leaves are to be preferred, but they seldom state why. The actual reason is the texture, they last longer than most and break down into discs rather than mush. For example, take the texture of the beech leaf compared with that of the apple or hawthorn.
The beech leaf dries crisply and the first stage is the break up into discs, which when added to potting composts keep it open and break down comparatively slowly. On the other hand, the apple and the thorn leaves are soft with no stiffness and the whole leaf curls up and eventually decays. This means that most of the home-gathered leaves are soft unless you have access to a road lined with beech trees or a bit of adjacent parkland or open space where beech and oak leaves can be collected and stacked separately to form leaf mould. Given the choice I prefer leaf mould and dried leaves any time to peat or any other alternative organic matter.
Three types of leaves which I always avoid are ash, horse-chestnut and willow. Not so much because of the leaf blades but because the thick stalks take at least twelve months to break down and decay and ash contains a certain amount of acidity which could be detrimental. However, a few of any of these mixed in with a sort of mixed grill of leaves generally found in the ordinary garden is acceptable. If you can afford one, a mincer to chop up all the organic debris is ideal.
I have never been very keen on putting lawn mowings into the compost heap which is kept for potting or for mulching because of the many seeds of Poa annua (annual meadow grass) it includes.
In late autumn when there are fewer seeds I do welcome a few lawn mowings and I achieve this by letting the leaves fall on to the lawn and then with a rotary mower slash the leaves to shreds whilst mowing the grass. They become thoroughly mixed together and form the basis of really fine leaf mould.
This mixture is either raked up or, in my case, collected into a large box and put into the compost bin. On top of every 4 inch layer, I sprinkle on a couple of handfuls of superphosphate. Superphosphate has two actions, it kills slugs and their eggs and helps to break down the compost, partly chemically and partly because of the minute traces of sulphuric acid it contains. It also supplies very valuable phosphates which are retained and not leached out and most garden soils are deficient in phosphates. A small amount of phosphate helps germinating seedlings and promotes sturdy growth. It has no ill effect on any other seedlings or plants which are potted up into it.
Many of my fellow gardeners ask if pine needles or those of other garden conifers, such as cupressus or metasequoia, can be added to the leaves. The answer is there is nothing detrimental in them, the only trouble being that they take about four times as long to decay as deciduous leaves because of the resin and turpentine they contain. Compost them separately and they form an ideal and durable mulch for most flowering shrubs. My favourite use for the true pine needles, however, is for the making of a top-dressing for paths as they form a dry durable weed-free surface.