All plants, indoors and out, need a plant feeding – an adequate supply of nitrogen, phosphates and potash together with small amounts of trace elements. Only then will they be capable of producing healthy growth with full-sized flowers and leaves.
When plant feeding in the garden, it is usual to apply fertilizers to top up the soil’s natural resources, but even in their absence the plant can continue to draw on the soil’s supply of nutrients by sending out new roots. Indoors the position is quite different.
The soil or compost in the pot containers a strictly limited amount of food, and this is continually depleted by the roots of the plant and by leaching through the drainage holes. Once the nutrient supply is exhausted regular feeding when the plant is actively growing must take place. Cacti can survive for a long time without any feeding, but vigorous foliage plants and flowering plants coming into bloom are seriously affected if not fed.
House plant foods are nearly always compound fertilizers containing nitrogen, phosphates and potash. By law the label must state the content of each of these elements; if there is no statement for one of them then you can be sure it is missing. Other plant feeding ingredients, such as humus extracts, trace elements, etc may be present.
Powder and granular fertilizers are widely used in the garden, but they are of limited use indoors. The plant food is deposited on the surface of the compost and it is not readily taken down to the roots where it is required. Furthermore you cannot cut off the supply when the resting period arrives.
Pills and sticks. Pushing a pill or plant feeding stick into the pot is certainly labor-saving, but there are important disadvantages. The nutrients are concentrated in one spot which does not promote even root development, and you cannot easily cut off the nutrient supply when the resting period arrives.
Liquid feeds. It is generally agreed that the most effective way to feed plants in pots is to use a liquid fertilizer. Watering and feeding are carried out as a single operation, thus saving an extra job and avoiding the danger of overfeeding. The recommended amount is added to the water, and this is used instead of plain water when watering.
Potting composts contain enough plant food for about 2 months after repotting. After this time feeding will be necessary, provided the plant is not dormant. The time to feed regularly is during the growing and flowering seasons – spring to fall for foliage and most flowering plants, and during winter for winter-flowering types. Plant feeding should be reduced or stopped during the resting period.