House plants are container grown and so they are inevitably limited in space and, therefore, in the amount of nutrients available. To ensure healthy growth, you must see to it that they obtain sufficient nutrients, which will usually mean repotting from time to time. Plants such as cyclamens, Sinningias and primroses, intended only for temporary decoration, are not repotted. However, plants that you want to keep for a number of years must be repotted regularly.

Use a rather light compost when repotting young plants for the first time because their roots are delicate and cannot tolerate heavy substrates. First of all, cover the drainage hole with a fairly large crock to prevent it from becoming clogged with compost but which will permit excess water to drain away. Then put in a thin layer of coarse sand, small crocks or fine gravel. Cover with a thin layer of potting compost. Carefully remove any dry, shrivelled or rotting roots and then place the plant in the pot. Cover the roots with compost sprinkled round the perimeter of the pot. Press it down with the fingertips. Finally, fill the whole pot with compost to within about 1 cm of the rim to allow a little space to prevent spillage when watering the plant.

The best time for repotting most plants is in spring; those that have a definite dormant period should be repotted just before new growth starts. Do not feed plants im mediately after repotting. Allow at least two or three weeks for the plants to become established. Then feed in the normal way.

Some plants, particularly those that spread readily and produce long shoots, should not be repotted. Rather, cut off the shoots and immediately insert the cuttings into fresh compost. This is the best method for growing Tradescantia, Zebrina and Scin-dapsus. Plants grown in a miniature conservatory or plant-case are not usually transplanted and neither are well-developed specimens of Ficus, Monstera, Philodendron and other large plants. It is important, however, that the container is large enough to prevent crowding of the roots. Handling such plants is very difficult. A simpler method than repotting is to remove the top layer of stale compost, replace it with fresh compost and give regular applications of extra feed during the course of the year.

Feeding houseplants

Because growing plants deplete the compost of nutrients, these must be replenished by the application of feed. However, over-feeding and erratic application will harm the plants, so it is necessary to observe some rules.

Apply feed only during the growing period, not during the period of rest.

Apply feed only to plants that are well established; not immediately after they have been repotted or when newly propagated.

Use only diluted solution. The proportions should be approximately 1-5 g of nutrient salts per 1 litre of water (0.08-0.2 oz salt per VA pt water). Follow the manufacturer’s instructions for the rate of dilution and the method of application – on the compost, on the foliage etc.

Regular applications of a small amount of feed of lower concentration is better than a single application of a stronger solution.

See the individual posts on particular plant species for precise details of their feeding requirements.

Feed for decorative plants may be applied in the form of organic or inorganic fertilizers. Organic fertilizers include farmyard manure, cow dung, bird droppings and horn meal. Cow dung is considered to be the best because it is tolerated even by tender plants and is longer-acting. In its dried form, it can be applied directly on to the compost in a ratio of one part cow dung to four parts compost. Fermented liquid cow dung diluted with water – one part cow dung to 10 parts water – can also be used. However, organic manures are rarely used on house plants because some have an unpleasant smell or are difficult to obtain. Inorganic fertilizers are a far more popular choice. These may contain a single nutrient – simple mineral fertilizer – or several nutrients – compound mineral fertilizer.

There are some special rules for feeding cacti and other succulents. It is particularly important to apply feed only during the period of intense growth and flowering. Species that flower in winter should be given applications of feed only at this time. How much and when to feed depends on the particular plant. One or two applications of feed during the growing season are enough for small plants; larger plants should be given greater amounts and fed more frequently. Plants grown in purely mineral substrates should be given regular applications of feed because they obtain no nourishment from any other source. Cacti should be given special cactus feed. This is also suitable for most other succulent plants. Only epiphytic species, such as phyllocacti, should be fed ordinary plant feed.

Feeding orchids is a complicated matter and those who are interested will find detailed information in specialist books. In general, the recommended dosage is a 2 per cent solution of compound fertilizier applied at two-week intervals, alternately on the compost and on the foliage.

Plants of the family Bromeliaceae do not like regular feeding. They should be fed only very occasionally with a weak solution of compound mineral fertilizer. Take care to avoid pouring fertilizer into the leaf rosettes. Organic fertilizers should never be used.

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