Afterthe next most important requirement is . Although all composts, other than composts, contain fertilizers in varying strengths, sooner or later these are exhausted. To keep a plant growing uniformly it is necessary to it. As with watering it is very easy to overdo it and give the plant too much food, so it helps to learn the requirements of the individual varieties. The first general rule is to feed a plant only when it isactivelygrowingand healthy. Never feed a dormant or really sick plant. If in doubt wait for a short while; it is generally better to underfeed slightly than to overfeed.
Why plants need food
Plants take most of their nutrition from the surrounding soil through thesystem, although some can be absorbed through the .
All plants, whether growing in the garden or in the house, need an adequate amount of nitrogen, phosphates and potassium. Nitrogen gives the rich green colour to the foliage, and potassium encourages the production ofand general vigorous growth. Phosphates are necessary for a good root system and growth. In addition most soils and composts contain trace elements, minute quantities of calcium, copper, iron manganese, sulphur, zinc and aluminium, which help growth. Houseplants cannot send out to tresh soil for their food, so they need fertilizer.