Specialized composts are also available, e.g. bulb fibre has charcoal added to keep it sweet in containers which frequently have no drainage holes, and orchid compost contains a large amount of coarsely pulverized bark to simulate growing conditions in their natural habitat. Ericaceous composts are ones which have no added limestone so are suitable for acid-loving plants. Some manufacturers provide kits from which you can make up your own composts, according to your needs, from peat, or peat substitute, sand, ground limestone and fertilizers, or sometimes supply kits of additives to mix with your own peat, or peat substitute. At the present time, it is my opinion that, while many peat-substitute composts are available, none of them produces the same results as a peat-based compost, and independent trials tend to prove this. They are also more expensive, so you may pay much more for much less — both in quantity and in results. Research continues and no doubt a product comparable with peat will eventually be found.
If possible, plants raised in soil-based composts should not be potted on into peat-based ones and vice-versa, as root systems differ according to which medium they have grown in, and will suffer a check if put into something different.
Growing bags are flattish, heavy-duty polythene bags filled with soil-less compost, the actual ingredients and their proportions varying according to manufacturer. These are useful for growing temporary crops of flowers, herbs, strawberries and vegetables outside or under glass and are especially handy for patios and other paved or concreted areas. They are supplied with instructions for planting up, quantities of plants, subsequent feeding, drainage, etc. depending on maker. Sometimes they can be used for two crops in succession but an imbalance or build-up of fertilizers can occur so, if in doubt, buy new, as spent growing bags will always come in handy for mulching or digging into garden soil to improve texture.
Like soil-based composts, most soil-less ones have a limited shelf-life because of the inclusion of quick-acting fertilizers. This can be considerably reduced if the bags are stored under less-than-ideal conditions, for example, in a wet yard. It is as well to purchase growing bags and compost from reputable suppliers who are aware of this, to avoid the chance of buying compost containing useless or even harmful fertilizer additives.
Potting composts are usually manufactured by well-known and highly respected firms and by buying names you recognize or those recommended to you, assuming they have been properly handled by the retailer, you should have no problems.
Growing bags, on the other hand, are a different matter. For a start, there tends to be a cut-price war among retailers, even with the ‘famous names’. These are always the ones to look for, and you ought to be all right, but some less responsible shops are able to cut their prices only because they are selling off old stock, which may or may not have deteriorated. A further complication arises in that many supermarkets sell cut-price bags under their own name. Some of these are actually made for the supermarket by the major manufacturers and there should be no trouble with these. Unfortunately, others produced by less scrupulous firms contain dubious ingredients producing poor results.
It is difficult to give any hard and fast advice, therefore, on how to choose growing bags. Perhaps the best way to go about it is to stick to the names you know. If anything should go wrong, these firms will always do tests for you to see if it is anything to do with them which is at fault, if so, they will be glad to know for their own reputation and will willingly replace. If the trouble lies with the retailer, they will be able to make the particular stockist aware of what is going wrong and give suggestions for improved storage. If the likelihood is that it is your technique which is lacking, they have advisory departments happy to put you back on the right road. So treat the nameless, cut-price offer with caution – it may not turn out to be the bargain you thought it was!