Not really a myth, and this notion is not generally acted on by experienced technically minded gardeners. It is just a gentle deception ‘sold’ to the gullible public that helps to keep the garden centre tills ringing.
Over the years I have noted on the gardening shelves of aunts and uncles - when I have been pressed into some gardening chore - lots of tiny packets just sitting there, never used, of all sorts of special concoctions for every plant they grow.
There is not usually anything wrong with these mixtures and they are certain to be much better than bonemeal. Rose fertilizer for example has a suitable balanced analysis that will be suitable for almost all of your plants.
|My balanced granular fertilizer. Granules facilitate ease of spreading. They are NOT slow release
John Innes composts
Before William Lawrence and John Newell developed John Innes compost at the John Innes Research Institute in the thirties it was generally believed that every plant needed it’s own special compost together with its own special nutrients. Recipes were closely guarded secrets of head gardeners and often went with them to the grave. Lawrence’s great contribution was that he showed that a simple series of composts could fulfill, almost, but not quite all, plant requirements. The four composts he developed were named J.I.Seed and J.I.Potting Compost, One,Two and Three. The only differences between JIP1, 2 and 3, was the strength of the fertilizer and lime, which increased three-fold between JIP1 and JIP3. It started to be whispered that these new fangled composts were much better than any of the old ones.
Unfortunately John Innes composts are not patented and any old rubbish can be sold as John Innes today. Modern mixes use more up-to-date fertilizer ingredients rather than the original formulae and there is nothing wrong with that. Plants that make vigorous growth and/or have a high nitrogen requirement are planted in the richer mixes. Delicate young plants must always be started in weak compost. J.I.Seed is now largely superseded by loam-less seed compost but J.I. Potting, if from a reputable supplier and certified by the John Innes Manufacturers Association gives excellent results. Alternatively you can mix it from your own from basic ingredients.
The point I am making with my long winded digression is that when it comes to giving nutrients to plants, simplicity is best.
Why I use just one general fertilizer and reject ‘special mixes’
- If general fertilizer has a fairly even balance and contains all the plant nutrients including trace elements, the plant will take from the soil what it needs.
- It is much cheaper to buy a large bag of a general fertilizer than buying lots of expensive little bags.
- It is easier and less time consuming.
- There is less wasted fertilizer when all those separate bags deteriorate on the shelf.
- There is no guarantee that special fertilizers are better for your plants. Their analysis might be due to popular fashion and is just as likely to be formulated by an adman or bean counter than a proper soil scientist.
- How do they know what nutrients my plants need? Does it not vary with the nature of the soil, season and weather conditions?
What about nitrogen?
In the wild plants greedily seek out nitrate because in natural soils it is usually in short supply. When fertilizer is used there is a danger that certain plants will absorb too much nitrogen and make unbalanced ‘soft’ growth susceptible to pest and disease. I avoid this problem because my general fertilizer has a fairly even nutrient balance. Where plants like brassicas and grass need higher levels of nitrogen, I merely apply a greater amount of my balanced fertiliser. It is much cheaper that way and any unused potash and phosphate remains in the soil for a future crop.
A much admired former horticultural colleague and very keen vegetable grower, in addition to his balanced fertilizer had a high-nitrogen fertilizer in his arsenal, the dreaded 20:10:10. Much used by farmers, it is horticulturally lethal in inexperienced hands!
Do you need to use any special fertilizers?
Slow release fertilizers may be appropriate if you are making up composts or preparing soil for tubs.
Certain nutrients can be ‘locked up’ in the soil. For example iron is frequently in short supply for acid loving plants grown in an alkaline soil. Some gardeners might need to supply trace elements in ‘chelated form’ (usually marketed as sequestrene).
Regular readers will know I am very partial to iron sulphate for my lawn!
The only liquid feed you need is a ‘tomato’ liquid feed. It is suitable for any of your plants.
What about lawn fertilizers?
I actually use my general fertilizer on the lawn! One hardly ever sees a lawn fertilizer these days that does not have added weedkiller or moss killer. Most lawn fertilizers are high in nitrogen which gives rapid growth of vulgar dark green grass. Personally I do not want to cause rapid grass growth. By all means use branded lawn fertilizers, but do not include me! I do not see many economies of scale when I see their price in the garden centre!
But don’t commercial growers use special fertilizers?
Many growers are specialists and grow very large quantities of a limited range of crops. They frequently have intimate knowledge and have technical advice as to their own plant’s precise and varying nutrient requirements. They have economies of scale when they buy. They are not paying premium prices for small bags! It makes sense for them to purchase exactly what their plants need.
I currently use this general fertilizer which I buy from a local horticultural supplier. A 25kg bag lasts me about two years.
I discuss my own take on compost in ‘Breaking the rules’