Watering, shade and ventilation This month, pay particular attention to watering. Plants in clay or terracotta pots may need two or more applications daily during hot weather. Maintain a humid atmosphere by frequently damping down, otherwise red spider mite may prove troublesome. Place pots on a gravel base kept as moist as possible. Apply extra shading in hot weather and, if the weather is very warm towards the end of the month, leave the top ventilators on the leeward side of the greenhouse open a little way at night. Transfer as many plants as possible either to cold frames or to a sheltered position outdoors. Artificial heating Towards the middle of the month artificial heat will not be required in a cool greenhouse. Clean the heater and store away until autumn. However, an electric fan heater with the heat turned off can be used in the summer to circulate air and help to keep the greenhouse cool. Controlling pests and diseases Pests will be particularly troublesome now, with the increased warmth and plenty of soft, lush growth. Be vigilant and consider biological controls for pests such as whitefly and aphids. Planting out In cold areas, plant out hardened-off plants after all risk of frost has passed. Sowing seeds Sow seeds of plants to provide indoor colour next winter and spring. Suitable plants for sowing now are cinerarias, calceolarias, primulas, primroses and streptocarpus. Taking cuttings Take softwood or semi-ripe cuttings of chrysanthemums, carnations, fuchsias, herbs and many perennials and shrubs, to root in the warmth of the greenhouse. A number of house and conservatory plants, including African violets and Bergonia res, can be propagated by leaf cuttings taken during the summer. Potting up and potting on Pot up any seedlings and cuttings taken last month that have now rooted. Check on any larger plants which may need moving into bigger pots. Streptocarpus sown at the beginning of the year should now be ready for potting on into 13-15 cm (5-6 in) pots. Handle the plants very carefully when you do this as the leaves are brittle and can be damaged surprisingly easily. Cucumbers Spray regularly to maintain a humid atmosphere for cucumber plants. Pick the fruits when they are about 30 cm (12 in) long. Melons Pinch out all but four sideshoots of melons planted last month in cold frames, stopping those shots when they have reached the corners of the frame. Wait until there is a female flower open on each shoot, then transfer pollen to them from the male flowers. Female flowers are distinguishable by the embryo fruit behind the flower head. Peppers and aubergines Water regularly and give a liquid feed every fortnight. Watch out for red spider mite and whitefly. Aubergines may also succumb to powdery and downy mildew. Tomatoes Water and feed regularly. Examine the mina stems of tomato plants and if they are starting to become thin, change to a liquid fertiliser which contains extra nitrogen. this will promote stronger growth. Vines Tie in shoots as soon as they become long enough. Water regularly and generously and feed every two to three weeks with a liquid tomato feed. Tap the branches or wipe a feather over the flower trusses in the middle of the day to assist pollination. There can be a conflict of interests between a vine and other plants. The moist atmosphere required by many greenhouse plants can encourage fungi and mildew on a vine, while the ideal temperature for a vine, at between 26-30°C (80-86°F), can be too high for other plants. So unless you have a greenhouse devoted to vine, you have to maintain a balance between sufficient ventilation and heat to suit the vine without overstepping the tolerances of the other plants.