Understanding Fertilisers

By Derek Brooks, Worsley, Manchester

There must be hundreds of people who join the ranks of "gardeners" every week, some of whom are persuaded to join the National Vegetable Society by friends.

All fertilisers contain at least one of the major plant foods-that is:

• Nitrogen (N)-for stem and leaf growth;
• Phosphate (P)-for root growth
• Potash (K)-for flower and fruit production.

Straight fertilisers supply only one major plant food. Compound fertilisers supply at least two major plant foods. Balanced or General fertilisers supply all three but not necessarily all in the same proportions.

Fertilisers can be either organic (derived from animal or plant remains) or inorganic (mined from the earth or man-made). Inorganic fertilisers are usually quicker acting. Fertilisers come in different forms, powder or granular for spreading on the soil and raking or hoeing in and as liquids or soluble crystals for applying with the watering can.

All proprietary brands of fertiliser, whether in bags or bottles, should display the analysis, or the N:P:K ratio. For example, if the N:P:K ratio is 7:7:7, as in Growmore, you know that the fertiliser contains equal proportions of the three major plant foods, nitrogen, phosphate and potash and is, therefore, suitable for general use with all plants.

Every plant requires all three major plant foods, but at different stages of growth they are needed in different proportions. For example a flowering or fruiting plant, which includes many vegetable crops, requires some phosphate in the early stages, to promote root growth, followed by a fertiliser high in nitrogen for the growth stage and then one which is higher in potash to ripen the plant and assist in flowering and fruiting.

The main fertilisers you will come across are principally used to supply plant foods as follows and I have classified them into the various types.

Straight fertilisers

Inorganic

Organic

Compound fertilisers

Inorganic

Nitrate of Potash - contains approximately 13% N, 45% K

Organic

Fish Meal - contains approximately 6-10% N, 6-12% K

General or balanced fertilisers

These are mostly proprietary products

Inorganic, powdered or granular fertilizers.

Growmore. Equal parts N,P,K. Mainly for incorporating in the soil before planting.

Rose fertilisers. Higher in potash than Growmore. Suitable for all flowering shrubs as well as roses.

Spring and summer lawn fertilisers. High in nitrogen to promote quick growth.

Autumn lawn fertilisers. Low in nitrogen, higher in phosphate (to strengthen roots) and potash.

John Innes base. Mainly for making compost to the John Innes formula. Add 4 oz per bushel (8 gal.) for J.I. No. 1.

Q4 base. Also for making potting compost. Rather expensive for use outside in the garden. Q4 HN is the same but higher in N.

Chempak base fertilisers. Mainly for making soil-less composts for seeds and cuttings or potting

Inorganic liquid feeds or soluble crystals

Chempack liquid fertilisers. Soluble crystals for applying with watering can. There are several different formulations for different purposes.

Phostrogen. Soluble fertiliser high in potash. Good for flowers and fruiting plants like tomatoes.

Miracle Grow. One of several new products ont he market. They are liquid fertilisers for general use.

Organic, solid fertilisers

Fish, blood and bone. For raking into ground before planting. High in potash by the standards of organic fertilisers, so, good for flower beds.

Calcified Seaweed. Similar to fish, blood and bone.

Organic Liquid fertilisers

Maxicrop. Made from seaweed extract. For general use on established plants.

Maxicrop tomato. Formulated for tomatoes, but good for any flowering or fruiting crop.

Baby Bio. Similar to Maxicrop, but mainly for house plants

How I use Fertilisers

So much for what is available, I will now describe how I apply fertilisers, with particular emphasis on vegetable growing. I have only a small vegetable garden, but I use a four year crop rotation. The only crops I do not rotate are onions, leeks and runner beans.

In the early part of the year I take a sample of each bed and analyse it. Based on the results of this analysis I then decide which fertilisers to apply before planting. The idea is to ensure that each crop has an adequate, but not excessive supply of the three major plant foods to begin with.

In nearly all cases, I use a balanced fertiliser such as Growmore or fish, blood and bone. The exception would be if any bed already has a very high level of one of the plant foods, in which case I would choose fertilisers which do not contain this food because an excess of a particular element, does more harm than good.

Nitrogen is rarely in excess because it is easily leached out of the soil by winter rain. Either of the other two could build up. If potash is in excess, the answer is probably fish meal.

If phosphate is in excess, however, the solution is usually a combination of two straight fertilisers, like sulphate of ammonia and sulphate of potash. I should add that I am not totally organic, but always prefer organic fertilisers if there is a choice.

Fertilisers for particular crops should be applied once the crop is growing, usually in liquid form, or easily soluble crystals. Some crops, like potatoes do alright with a balanced fertiliser, like Maxicrop all the time.

Onions and leeks are given high nitrogen fertiliser during the growing stage, nitro chalk, or nitrate of soda, and in the case of onions, one with a higher potash content later on to ripen the bulbs.

Leafy crops such as cabbages get high nitrogen feeds all along. Beans and peas are happy with Maxicrop while they are growing and then Phostrogen later on during the flowering and fruiting stage, because this contains more potash.

I said earlier that root crops require phosphate. I have never found, however, that they need extra doses while growing. There is enough in the ground to begin with, I do not feed these crops much, but if I do, a general fertiliser is adequate.

I hope you understand the use of fertilisers a bit more after reading this article. By the way, do not be worried if you have not got facilities for soil testing. If you are keen, you can send it away for analysis to one of the firms you see advertised. If you don't want to go to this trouble and expense, you can't go far wrong with a base dressing of Growmore or fish, blood and bone and then follow the other steps which I have described.

Did You Know?

Growmore, probably the most popular compound fertiliser, was first formulated as part of the "Dig For Victory" campaign in the Second World War-hence its full name "National Growmore"?

Wilted comfrey leaves are an excellent source of organic potash? Use them around soft fruit or when planting potatoes. Or add them to the compost heap at any time. Cultivated strains are available but don't despise the wild plant which grows beside ditches on many allotment sites.

Site Map | Home | About NVS | Grow & Show | Web Links | News & Events | NVS Shop | Contact | Access | Privacy

Copyright © National Vegetable Society 2006-2007 Design WebOneUK Problems with this site - email
Registered Charity No. 1088979