It was discovered many years ago that growing in containers or planters
is completely different to normal gardening. The most important discovery was that normal soil just will not work in planters. It is far too dense, contains unwanted micro organisms and is full of dormant seeds just waiting to germinate. Here are a few tips on how to avoid problems with the planting medium in your planters.
- Moisten planting medium before filling your planter and planting up.
- You should not leave unused planting medium open. The mix will dry out and degrade. You will have wasted some of your hard earned money.
- Normal compost is far too heavy for your planters. It will not drain very well and will harden into a solid block if it dries out.
- Soil less planting medium is used for seeds they are not intended for use in planters or adult plants.
- Different plants need different conditions, different planting medium with different nutrients and pH levels. So check the planting instructions.
- When mixing your own planting medium and you are using peat, coir or another form of organic material please check the pH. Perhaps you will have to add lime to prevent the mix from being to acidic.
- There are two basic kinds of compost: those containing soil and those that are soil free and are based on peat. If you are concerned about the environmental effects of cutting peat, choose a soil-free compost made with a peat substitute. These are usually based on coir, and may need extra fertilisers and more frequent watering.
Proprietory 'planter' or 'multipurpose' composts are generally soil-free with a slow-release feed, wetting agent and sometimes with water-retaining gel added.
All soil-free composts contain additives. Such as lime to reduce their acidity, sharp sand to improve drainage, and a fast-acting fertiliser. They are excellent for a summer display, but tend to tire quickly, so are less suitable for permanent plantings. Lighter than soil-based composts, they are a good choice for balconies and roof gardens. Composts containing soil are a mixture of loam, peat and sharp sand, and are largely based on the 'John Innes' formula. They contain varying amounts of fertiliser, depending on what they are to be used for. John Innes No.1 contains very little fertiliser, making it suitable for young plants, which do not grow well in high levels of plant food. John Innes No.2 has twice as much fertiliser as No.1.
It can be used for fast-growing young plants and for slow-growing plants which will be over-stimulated by too much fertiliser. For large or mature specimens use John Innes No.3. This contains three times as much plant food as No.1 and will sustain plants in the same container for several years. If you want to grow thriving acid-loving plants, such as rhododendrons, you will need an acid compost. These composts are lime free and are usually labelled 'ericaceous'. They also have plant foods added. Some arrangements are so dense that the surface of the compost is hidden. However; if the compost is exposed, it is vulnerable to invasion by weeds, and moisture will evaporate from it in hot weather, making frequent watering essential. The answer is to cover the compost with a layer of mulch which will help to reduce these problems. Bark chippings and cocoa shells sold for mulching garden borders are also suitable for planters.