Many apparently healthy house plants will suddenly sicken and die when theirhas become saturated with water. Waterlogged compost excludes necessary oxygen from the area around the plant , and then the plant simply ‘drowns’ in the water as it is unable to breathe. A free-drainage compost will prevent this happening, by allowing excess water to escape and air to enter.
However, most plants need to be kept quite moist when they are growing vigorously as they will suffer when dry, especially during warm weather. In high temperatures, plants keep themselves cool by increasing their rate of transpiration, the normal escape of water from theinto the air. This in turn increases the plant’s need for additional water. Lack of water at this stage can lead to wilting and may prove fatal. Some of the less common drainage materials — mineral wool, for example —soak up excess water when the compost is too wet, and then gradually release it when the plant begins to dry out.
There are various types of drainage material on the market, new and old, natural and man-made. The use of some of these substances was first pioneered by professional gardeners and they have only recently become readily available to the amateur. Loose, granular drainage materials can be mixed in different ratios with both soil- and peat-based compost, depending on a plant’s individual requirements.
Other substances are used in mat or blanket form, to make a drainage layer either below the compost or directly beneath the pot. A third type of drainage material can be broken up and mixed with compost in the same way as granules or used in solid blocks as an alternative growing medium, provided that a constant supply of fertilizer and water is available.
Broken terracotta or clay any pot shards from plantmake excellent broken plant drainage material for use together in a sturdy hanging plant containers. Keep for use when necessary. Pot shards used to be the most common form of drainage for house and conservatory plants grown in containers, but as the use of plastic pots has increased there are less available. Break up into small pieces any clean, discarded clay pots you have and place a thin layer in the base of the . Excess water will drain down to this layer and be absorbed by the clay, which will release the moisture later when more water is needed by the plant.
Granular drainage material
The addition of one part of washed grit or coarse sand to two or three parts of compost is a tried and trusted method of improving the quality of drainage. Both substances open up the structure of the compost, allowing water to drain away freely. Don’t use sand from the seashore, as this may contain harmful salts which will damage the roots of the plants, but buy from a local garden centre. A thin layer of fine sand sprinkled on the surface of seed compost will aid drainage and help prevent fungus infections.
Perlite (sterile volcanic rock), vermiculite, flakes of expanded mica and polystyrene granules can all be mixed with compost in the same way. They not only improve drainage, but increase the volume of the compost and will ensure a good amount of air around plant. They also have the advantage of being clean to handle, light in weight and will retain a certain amount of water.
Leca and gravel
Leca is a man-made stone which is very light in weight. It looks like small, brown pebbles and is available in several grades from large garden centres and nurseries. Use leca at the base of a n the same way as pot shards, although leca will not absorb water in the same way. This substance is often used to replace the top 25mm (1 inch) of compost in large containers. It not only looks more attractive than bare compost, but prevents evaporation in hot weather and stops the compost being disturbed when the plant is watered. A layer of the finest grade of leca is often used on the surface of the compost to improve drainage when growing cacti. Gravel in various sizes and well-washed pebbles can be used in the same way, but they are much heavier.i
There are several products available that contribute greatly to improved drainage and, all of which are stocked by good garden centres. From left to right: capillary matting, leca, vermiculite, washed gravel, free-draining compost, perlite, washed sand, charcoal and, in the tray, a finer grade of leca.
Providing good drainage is an essential part of keeping plants vigorous and healthy. Traditional methods still prevail, and there are also new and interesting products available.
Two fairly new drainage materials are becoming widely available to the home gardener. Fibertex and mineral wool can be purchased from specialist suppliers by post and can be found in some large garden centres and nurseries, under a wide range of proprietary names.
Fibertex comes in the form of a thick mat or blanket which is capable of absorbing large quantities of water, then releasing it as needed. Use Fibertex as a watering mat by placing a layer in a watertight tray or plastic dish under the pots. Water the Fibertex instead of the plant, which will then be able to draw up moisture when needed. Another way of using Fibertex in large containers is to place a thick layer over pot shards or leca before adding compost in the usual way. This will improve drainage considerably.
There are various kinds of mineral wool which can be broken up andadded to the compost. All types improve drainage, but some will also absorb and release water as needed. Plants can be grown in blocks of mineral wool, either in the home or on the balcony or. As mineral wool contains no nourishment, a constant supply or fertilizer and water is necessary. This method is the one most often used to grow tomatoes.
When using a container without drainage holes – when planting up a horde garden or bulb howl, for example – you need to add charcoal. This not only improves drainage by absorbing excess water to prevent the roots from rotting and ‘drowning’, but it also absorbs excess mineral salts and decayed matter, keeping the compost fresh and `sweet’.
Add a thick layer of charcoal pieces to the bottom or the container before biting it with the appropriate compost. Tiny pieces of charcoal can also be mixed in with the compost to keep it even more ‘sweet’.