Ventilation and watering plants On sunny days ventilate the greenhouse freely; avoid cold draughts, and close the ventilators fairly early in the afternoon to retain some of the daytime warmth. Dirty glass excludes valuable light, so use warm water containing detergent to wash it. Keep the greenhouse closed during foggy weather, and cover the plants with newspaper or horticultural fleece if the fog persists. Water all plants sparingly and keep the atmosphere as dry as possible. Pests and diseases Whitefly are often troublesome in the greenhouse at this time of year. Treat at the first signs of an attack. It will be too late for natural predators to multiply in sufficient numbers to act as a control. If using a spray, beware of increasing the humidity of the greenhouse too much; fumigation may be more appropriate. Potting up Complete any outstanding potting up early in the month. Annuals raised from seed in September will probably be ready for moving into 13 or 15 cm (5 or 6 in) pots. Pot up sweet pea seedlings. Cuttings of pelargoniums, fuchsias and other plants inserted in September should now be rooted and also ready for potting individually into 8 cm (3 in) pots. Overwintering Allow pots of begonias, achimenes, heliotropes and hydrangeas, which have flowered during the summer and autumn, to dry off. Store the pots under the staging in a cool greenhouse or in a frost-proof shed, but do not allow the compost to become dust dry. Some fuchsias may also be treated in this way. Check dahlias in storage and any bulbs being forced for winter flowering. Forcing hardy plants Many hardy plants will flower early indoors if lifted now from the garden and potted into 15-18 cm (6-7 in) pots, depending on the size of the roots. Examples are aquilegia, bleeding heart, polyanthus and Christmas rose which flowers at Christmas if grown under glass. move pots into the conservatory or house when they come into flower. Vines Begin pruning vines once the leaves have fallen. Plant new vines between now and the end of the year. Although the ideal place is in the greenhouse border, the roots will soon take up growing space needed for other plants. An alternative is to plant vines outside and then lead the main shoot through to grow in the greenhouse. Vines succeed with this method, despite the disparity in temperature between the roots and top growth. Dig a hole large enough to spread the roots out well, but do not add manure or fertiliser - vines, figs, grow on poor soil in their native habitat. Cut back the shoot by two-thirds after planting.