Frequency of watering can vary from twice a day in the heat of summer to once in two days in a cool greenhouse in winter. If a capillary bench is in use the problem does not arise. In summer when in doubt give water, in winter when in doubt withhold it; but when water is given it should be sufficient to wet all of the compost in the pot. Most plants prefer rain water if it can be collected and stored for them, and for orchids and ericaceous plants it is almost essential. Feeding Feeding should be started as soon as plants are well rooted in their final containers. This is of particular importance when peat-based composts are used as they cannot carry a reserve of plant foods so readily as loam-based composts, although modern slow-release fertilisers help in this respect. With most plants feeding should start about six weeks after potting, and as a rough guide feeds should be given once a week in spring and summer, once a fortnight in autumn and occasionally in winter. The exceptions are those plants which grow throughout the winter to flower in spring. These should be fed while in growth; bulbs and corms also in the early stages of ripening. All plant feeds should show an analysis on the pack; in winter high potash feeds should be used while in summer feeds should be chosen to suit the plants grown. Foliar feeds are of special use in giving backward plants a boost or for feeding plants which may resent chemicals in the compost, as might orchids or other epiphytes. Humidity Control This is usually associated with the frequent damping-down of floor and staging in a greenhouse on a hot day. Maintaining a moist atmosphere in summer is an important factor in keeping plants healthy and discouraging pests. In a cool greenhouse in winter atmospheric moisture can aggravate disease problems and humidity control takes a reverse role. Drips from can or lance, water spillage in any way must be avoided in the effort to maintain dry air in the greenhouse. Light and Shade In October, or as soon thereafter as possible, the greenhouse should be thoroughly cleaned down, the glass scrubbed to remove any persistent deposits, old shading paint or algae, and the glass overlaps cleared with a forceful jet of water and the aid of a thin plastic label. The object is not just to ensure a clean start for the new season, but to give the occupants of the house the maximum possible light in winter; this helps all plants but is particularly advantageous for crops of winter lettuce. In summer the sun becomes too hot under glass (see comments on roller shades, p.275) and from about the end of March to the end of September some form of shading is required, either as roller blinds, open-weave plastic material erected in the greenhouse or as paint-on shading. A green colour is mostly chosen but white is marginally better for plants and lets through more light when wet. Hygiene Good hygiene will help to keep plants disease- and pest-free. Dead leaves, flowers or plants should be removed and destroyed.