How Do Garden Fertilizers Work?
How Do Garden Fertilizers Work?
Some garden plants and many weeds are particularly good at accumulating very large amounts of minerals and trace elements. This is despite the soil being deficient in whichever mineral they accumulate. In fact, these plants often abound on deficient soils just because they are the most successful at grabbing a scarce resource. As they extract available nutrients from the soil water, the nutrients are replaced by more that are dissolved from otherwise insoluble mineral sources. In this way, they can go on accumulating from very dilute solutions. If you grow these plants as they will remove the scarce resource while they are alive, but once composted, the concentrated material can be put back to boost the soil.
Nitrogen is best accumulated with leguminous plants, and by incorporating any succulent seedlings in their first flushes of growth.
Phosphorus is concentrated particularly by the weed fat hen, corn, purslane, vetches and the pernicious weed thorn apple (Datum stramonium).
Potassium, which encourages fruiting, is accumulated by chickweed, chicory, fat hen, goosegrass, plantain, purslane, thorn apple, sweet tobaccos and vetches.
Calcium is concentrated by buckwheat, corn chamomile, corn marigold, dandelion, fat hen, goosegrass, melon leaves, purslane and shepherd’s purse.
Silica imparts disease resistance and is made active by plantains, couch grass, stingingand the most perfidious weed Equisetum.
Sulphur aids disease resistance and accumulates in the onion family,, fat hen and purslane.
Other minerals are accumulated by many plants, and especially by weeds, some if which are worth tolerating for this and other reasons.
Conventional fertilisers are ranked according to their Nitrogen, Phosphorus and K (potassium) ratio and content. These are regarded much as direct plant foods replacing these elements taken away with the crop. Nitrogen is considered to stimulate growth and leaves, phosphorus the roots and potassium fruiting and disease resistance. While it is true these same elements exist as salts in the soil solution naturally, it is not natural to have them in very high concentrations as occur when they are applied as conventional soluble fertilisers.
Organically, we guard the micro-organisms in the soil by not using any substances that can damage them, so we apply fertilisers that are effectively insoluble and cannot become too concentrated. These need to be broken down and incorporated by micro-organisms before they can increase the nutrient supply in the soil solution and be available to plants. Thus they do not leach as readily and are longer lasting. They may be considered more as soil stimulators than as plant fertilisers as they promote increases in soil life, and the by-products from this increased population then feed the plants. Because they are stimulators or catalysts they do not need to be applied heavily, rather it is better to spread them thinly and more often than in massive doses. In established gardens every other year is sufficient.
Be aware that providing a disposal method for their wastes is effectively supporting the factory farming they come from. Litter from very intensive units may also contain unacceptable residues. But one often takes what one can get — better that we use such wastes productively than let them go into landfill sites. All animal manures contribute directly and indirectly to soil fertility, but should always be well composted first. In order of preference I choose: horse,then goat which are all sweet to handle; cow muck is less pleasant; pig is vile and often contains unacceptable contaminants. Rabbit and pet droppings can be added to the compost heap, but cat and dog litter is best pit buried under trees. Poultry manures are very strong, highly nitrogenous and a good source of potash. They certainly make a compost heap cook! Never put these raw droppings on plants, always compost them first. Commercial poultry composts are acceptable if organically qualified.
Human liquid waste is not a health hazard in temperate climates, and it is wasteful to use a couple of gallons of water to flush such a rich source of fertility down to the sea. Saved in a bucket it can get quite smelly, but then makes a superb compost activator. Alternatively, apply each day’s quota directly to the heap. Recycling personal solid wastes is not for most of us; though ecologically desirable, it is difficult in practice. Sewage sludge is also likely to be contaminated so is only recommended for ornamental plantings where it can be used as a slow release source of phosphate.
Traditional organically based fertiliser — blood, fish and bone meal — is first-rate in performance, but not so good on ecological and compassionate grounds. Many people find it unpleasant to handle, but it is very effective and fast acting. It should be used in moderation, raked in immediately before planting hungry feeders. Beware, cheap brands are frequently adulterated with chemical fertilisers and sand. Bone meal is unsavoury to many, but is an excellent source of phosphates, which make up about a third of it. The finer ground the bone meal, the faster acting it is. It is expensive, but good for incorporating when planting, especially for woody plants and. Hoof and horn is just that, equally unpalatable and very expensive, but an effective slow-release source of nitrogen for hungry and woody plants. These last three fertilisers are all likely to be pinched by animals or birds unless mixed in well with the soil, so keep the bags in a safe, dry place.