In the greenhouse
Open doors and vents on greenhouses to increase ventilation on warm, sunny days.
Damp down the floor of the greenhouse regularly on hot days, to increase humidity levels. This benefits plant growth and also reduces the risk of pest problems such as glasshouse red spider mite. Give plants a liquid feed to encourage flowering and fruiting.
Apply shade paint to the outside of the glass or use blinds on sunny days to prevent temperatures from soaring.
Don’t forget to give greenhouse plants more space as they put on new growth. This will help to prevent disease, and to contain early pest infestations.
Check plants at least every few days, to see if they need watering. Seedlings will need daily attention. Use rain, grey or recycled water wherever possible.
Continue to prick out and pot on new seedlings and cuttings.
Harden off half-hardy bedding plants that were started off under cover.
Some conservatory plants such as Cymbidium, yuccas and Citrus can be moved outdoors for a 'summer holiday' once all risk of frost has passed.
Pot up houseplants showing signs of being rootbound or topdress large containers with fresh compost.
Pruning and training
Train the new stems of passion flowers, jasmines and other climbers over frames or on horizontal wires.
Pest and disease watch
Vine weevil larvae can be a serious pest of containerised plants, and become active this month. Tip out the rootball of suspect plants, and inspect for the creamy, orange-headed maggots, which tend to curl up into a ‘C’ shape. There are biological controls available.
Regularly inspect plants, and also the structures of the greenhouse and conservatory, for glasshouse red spider mite, whitefly, thrips and other pests. Paying careful attention to the undersides of the leaves, and to each plant in turn, can spot early infestations that would otherwise be missed. Remove by hand or use biological controls.
Brush up fallen compost and debris, and pick off dead leaves from plants. This will help prevent pests and disease spreading.