Importance of Garden Fertilisers

This is an insight into what fertilisers contain and how much. First, though, a quick comparison between organic and inorganic fertilisers. 

Organic Fertilisers

Organic fertilisers usually contain less plant foods. This means that more needs to be applied but it also makes them safer to use, from the plant’s angle; it’s harder to give a damaging overdose, Their nutrients are normally slower to become available but are released over a longer period. They aren’t always easy to buy, and they are more expensive. 

Inorganic Fertilisers

Inorganic fertilisers, on the other hand, are cheaper and much more readily available. They contain a higher proportion of plant foods and, therefore, less needs to be applied, but they are more likely to cause damage if an overdose is given. It is much easier to make, and therefore buy, inorganic balanced feeds. They are normally quick acting.

 One thing you can be sure of is that the plants can’t tell any difference. All have to be broken down by the soil micro-organisms into chemicals that can be absorbed by the roots. By the time this has happened, they bear no resemblance to their original form.

Something else that is often put forward on their behalf is that organics supply the ground with organic matter. Technically, this is perfectly true but the amount that they add is minute and too small to have any significance at all. They are applied at a few ounces to the square yard. To do any good, organic matter has to be put on by the barrowful.

None of this means that I am either for or against either group of fertiliser, but ‘organic freaks’ tend to attribute organic fertilisers with grossly exaggerated properties. They are merely organic sources of plant nutrients; nothing more. Both types have their virtues and vices but I would be loath to bear the added cost of organics on the allegation that they are better for the plants and/or the soil. If you want to use them, by all means do but please don’t run away with the idea that they have any mystical powers.

Back to the full range of fertilisers now. The conventional way in which they are classified is in terms of their N, P and K content, those elements needed in greatest amounts.

The simple explanation for the large number of organic materials containing nitrogen is that it is part of the protein molecule and, as such, is found in virtually all living things.

All fertilisers offered for sale must carry in writing on the pack the percentages of the different elements. Two terms often crop up in relation to fertilisers, especially those containing nitrogen: ‘slow release’ and ‘quick release’. These refer to the speed with which the nitrogen, or other element, is released from the fertiliser and is available to plants.

Which one is the more suitable to use will depend largely on the time of year and the crop in question. For example, fruit trees and bushes prefer a slow release form, like hoof and horn, because the nitrogen is released over a longish period rather than all at once in a rush. Lettuces and other fast growing vegetables are better with a quick release fertiliser that gives them a boost when they need it.

Moving on to those fertilisers used for their phosphate content – there are not nearly so many phosphatic fertilisers to choose from. However, phosphates are not used by plants in large amounts and, being comparatively insoluble in water, they tend to remain in the soil longer than nitrogen and potash, so less needs to be applied. Often, in fact, applying phosphates every other year is perfectly adequate.

Bones are one of the main sources of organic phosphates.

Potash fertilisers are less plentiful than those high in nitrogen, but there are still several to choose from and it must not be forgotten that some of those already mentioned contain useful amounts of potassium.

One thing that all the above fertilisers have in common is that they are in a solid (dry) form. That is, they are applied to the ground dry and as they are bought. They then have to be either dissolved by rain or irrigation water or be washed into or incorporated into the soil before being converted into a form that is available to the plants. This is not always convenient, and sometimes a liquid feed is better, as with plants in containers.

Garden compost can be hung in a tub of water to produce a very useful liquid feed for plants, and this can also be done with farmyard manure to give us manure-water (bearing in mind that the smell is not always socially acceptable when used indoors). Dried blood is fairly soluble in water and makes a good nitrogen feed when dissolved at the rate of 1 oz in 2 gallons of water. This is first-rate as a tonic for the plants. Various other concoctions and infusions have been dreamed up over the years but none seem to have any particular advantage over the more orthodox ones.

There is one material, however, that is possibly better than most others as a liquid feed — concentrated seaweed extract (Maxicrop). This is available in several formulations, some of which have man-made soluble fertilisers added to increase the strength and suitability of the product for different crops. The one described as ‘natural’ is the pure seaweed extract with no additives.

This particular type of feed has a number of advantages, Firstly, it is a complete feed in itself; trace elements are included. Secondly, it is excellent as a foliar feed (one applied to the leaves with a watering can or sprayer) as well as a root fertiliser. Thirdly, it is equally suitable for mature plants as well as for new seedlings.

Having mentioned these three main ways of feeding plants, dry and liquid root fertilisers and foliar feeds, it’s vital to look at the advantages and disadvantages of each to decide which is the best type to use for a particular job.

Dry Fertiliser

There is no doubt that dry fertilisers are the most convenient to use. All you have to do is open the pack, take out a handful and sprinkle it on the ground. If it is being applied as a base dressing before sowing or planting a crop, it would be cultivated in as a matter of course. If it is used as a top dressing, it would be hoed in.

Where the soil is dry, watering helps to speed up the fertiliser’s action, otherwise you just sit back and wait for things to happen. The normal system with vegetables is to apply only a base dressing before sowing or planting to quick growing crops, like lettuces, other salads and summer cabbage, but follow this with a top dressing for those vegetables that crop for a long time. French and runner beans and peas are good examples of these.

The normal inorganic fertiliser used for both purposes and for all vegetables is Growmore. This first saw the light of day during the last war when it formed part of the ‘Dig for Victory’ campaign to encourage people to grow their own vegetables at home. It’s still going strong and, for a general purpose fertiliser, has yet to be beaten.

The main reason for Growmore’s success is its relatively low and safe (to plants) nutrient content (NPK 7:7:7) but there is ample of all three of the elements most in demand by the majority of plants. For the organically minded, Blood, Fish and Bone is the equivalent at about 6:7:6.

Experienced gardeners will realise that dry fertilisers have one important shortcoming; they need water to dissolve them so that they are in a fit state to be acted upon by the soil microorganisms before being absorbed by roots. If they remain dry after application, they are, of course, completely useless. This is a fairly rare occurrence in the UK but it does sometimes happen to top dressings in the summer. 

Liquid Fertiliser

If plants need feeding during periods of drought, and many will, the answer lies in the use of a liquid feed, which serves the double purpose of supplying both water and nutrients, In addition, because the nutrients are already in a dissolved state, they have the benefit of being quickly taken up by the plants. You can make use of this virtue at other times when a rapid response is wanted, and when feeding plants in containers.

Unfortunately, liquid feeds also have a slight snag. As a direct result of being readily soluble and quickly available, they are also soon used up or washed out of the soil and need to be replaced more frequently than dry fertilisers. The speed of their disappearance is dependent on such things as the type of soil (heavy soils retain them longer) and the rainfall.

A very general recommendation for using liquid fertilisers to feed vegetables growing in the open ground would be to apply them about every three to four weeks. 

Foliar Feeds

If a really quick response is wanted, a foliar feed, such as seaweed extract, should be used. The elements within these are readily absorbed by the leaves as well as by the roots and, because the material is sprayed on to the leaves, the response is almost immediate. That’s a rather grand claim, but you could expect to see results in well under a week during the summer.

Incidentally, older gardeners may well remember the popularity of soot-water. This was made by hanging a bag of soot in a water butt in the same way that one does with farmyard manure or garden compost. The resulting brew made a good foliar feed by supplying nitrogen. It also had some powers of dissuasion towards certain pests and diseases.

The important point about foliar feeding is that it should never be regarded as the main way of feeding plants. Unless you use a complete feed, like seaweed, the diet is likely to be incomplete and, besides that, it would need to be applied so frequently as to become a chore. The roots are the organs that plants use for absorbing food; keep it that way.

Foliar feeding really comes into its own when a plant is suffering, or when you want it to put in just that little bit more effort, or at a naturally stressful time, such as during the flowering period of peas and beans, when a little extra help will pay dividends. Plants that have recently been moved will derive enormous benefit from a foliar feed because it will sustain them until the roots have become established and can take over. Also, by strengthening the leaves and making them operate better, foliar feeding will encourage the roots to grow and take over all the quicker.

 Those, then, are the three main ways of feeding plants, and circumstances will dictate which is best for a particular type of plant at a given moment.

Plant nutrition is an extremely complicated science, but fortunately we don’t need to know the whys and wherefores of it all because Mother Nature has endowed plants with almost boundless tolerance. However, a bad gardener, or one who fails to feed his plants properly, will soon find out that there is a limit to their endurance. It is worth bearing this in mind if you like to garden ‘organically’ because the fertilisers involved cost a good deal more than artificials. As a result of this, there may come a time when it is felt that putting the plants on a diet to save on the cost of fertilisers will do no harm; it most certainly will.

No account of plant nutrition would be complete without a look at the biochemical world of what part the most important elements play within the plant. Understanding a little of this helps the gardener appreciate which elements are the most important for a given crop, and why. This, in turn, will make it possible for you to buy a more specialised fertiliser if needed.

Nitrogen, the first to be considered, is used for leaf and heart production, as in lettuces and cabbages; it gives bulk and size to a plant and the rich green colour we all associate with a healthy and well-fed vegetable. Also, it is part of the protein molecule found in all cells and, therefore, a shortage will lead to smaller cells, and thus smaller plants.

As part of the chlorophyll molecule, a shortage of nitrogen will also lead to pale leaves and therefore, again, smaller and less productive plants.

Phosphates are important for good root development, quick establishment, early maturity and the ripening of seeds and fruits. A shortage will slow down cell division at the growing points, and hence slow down growth. Phosphates also help with photosynthesis and disease resistance.

Potash encourages balanced growth, by reducing the effect of nitrogen, and improves the quality of fruit and flowers. It also gives better frost and disease resistance. Potash is another element that plays a part in photosynthesis (the conversion of gaseous carbon dioxide into solid carbohydrates) and therefore a shortage will, again, slow down growth.

Calcium plays an important part in the growth process by being a major constituent of the walls of individual cells. A shortage will lead to a reduction in cell formation and diminished root systems with reduced mineral uptake.

Calcium, in the form of chalk and lime, will reduce soil acidity and will make heavy soils easier to cultivate by drawing together the tiny particles into crumbs and blocks, thus giving the soil a better structure.

Magnesium is yet another part of the chlorophyll molecule, with all that implies. Anyone who has grown tomatoes will probably know what a shortage looks like; a yellowing between the veins of the older leaves and, therefore, reduced cropping as well as slower growth.

The only other element you are really likely to have any dealings with is iron. However, it’s very seldom that vegetables suffer from a shortage; the usual victims are ericaceous plants (rhododendrons and azaleas) growing on a chalky soil. Luckily, vegetables are remarkably free from this sort of trouble.

The latest thing in plant nutrition is a product called ‘Pea and Bean Booster’. This is an inoculum of the naturally-occurring bacterium Rhizobium that is found in the root nodules of all peas and beans. This bacterium ‘fixes’ the raw materials for making nitrogen for the host plant to feed on. Thus the nitrogen-fixing bacteria are in the soil, around the roots, right from the word go. It really does give the crops a kick-start and I wouldn’t mind betting that other similar products will follow.


16. June 2013 by admin
Categories: Fertilizers, Garden Care, Garden Management | Tags: , , | Comments Off on Importance of Garden Fertilisers


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