Greenhouse Tasks for the Summer

As spring slips seamlessly into summer, the hard work and preparation that has gone into the greenhouse since the last growing season begins to pay off in all its glory, as the staging heaves under the weight of fresh, verdant growth. With nature at her most productive, greenhouse plants – and those which were reared under glass and then planted out in the garden – should be at their best. A few important jobs around the greenhouse at this time of the year will help to ensure that they are.

The Greenhouse in Summer

In terms of greenhouse management, there are three key elements to success throughout the summer months – watering, ventilation and shade. In the height of summer, plants will be using water at an alarming rate and it is no use waiting until they are showing all the signs of wilting before watering them.


Whether it is done manually or automatically, adequate watering is crucial and must form part of the daily regime – typically night and morning. Plants in clay pots may need watering more than twice a day in hot weather when evaporative losses are high and unless the atmosphere is kept humid by frequent damping down of the paths and staging, an outbreak of red spider mite may cause you some trouble. If this miniature pest does get a grip, however, all is not lost – a predatory mite is now available which can provide a very effective biological control in the greenhouse environment.

Shading and Ventilation

In particularly hot spells, extra shading may be needed during the day and the upper ventilators left open at night unless the forecast suggests particularly cold or windy weather, when only the ones away from the prevailing wind should be open, to avoid chilling draughts. Adequate ventilation is vital to avoid overheating; depending on the siting of the greenhouse, the early morning sun can raise the temperature surprisingly quickly in the summer. If this is a problem, it may be worth considering fitting one of the various types of automatic systems on the market, which will open up the vents for you.

In most years, supplementary heating can be switched off in a cool greenhouse by the middle of June – though if you use a fan heater, it can be helpful to keep it running on “cold” to circulate the air in hot weather. Alternatively, free standing fans can be brought in to do the same job when there is a need for additional ventilation.

With the warmth and so much lush growth on offer, pests can prove a particular nuisance in the summer, making keeping a careful lookout for the first signs of trouble especially important. The warm conditions allow many species to breed prolifically – but fortunately the greenhouse environment is very well suited to modern biological controls, which can deliver effective protection without the need for pesticides.

Plant Propagation

The summer greenhouse is largely about maintaining and caring for the plants which were started off in the spring, planting out, potting on and tending them as necessary, the seeds of summer success quite literally having largely been sown before. In early summer, it is worth considering sowing plants which will be able to give indoor colour during the winter and spring months – cinerarias, calceolarias and primulas, for instance. Now is also the time to think about taking leaf cuttings from plants such as African violets and begonias and semi-ripe cuttings of the likes of chrysanthemums, carnations, fuchsias, herbs and hydrangeas, selecting healthy, greenish brown shoots for propagation. Seedlings and rooted cuttings which were started off in the spring will need to be potted up.

As the summer progresses, any climbing plants grown along the greenhouse walls will need to be regularly tied in to prevent them taking too much light from other plants and if peaches and vines are being grown, they will need routine thinning to improve their yield. Likewise, cucumbers and melons must be regularly supported and tied and tomatoes need particularly attentive feeding and watering, coupled with careful side shoot removal to encourage good cropping. As the end of summer approaches, fuchsias will need to be potted up and a watch kept for the onset of lower night temperatures which begin to bring condensation and the possible threat of mildew – though keeping the air moving and good ventilation should help.

The summer greenhouse is a place of colour and plenty, representing the culmination of all of the preceding months of hard work and preparation – the high-point of the glass-house grower’s calendar. As summer draws to a close and the last of the produce is picked, however, the wheel turns once again and it is time to begin thinking about autumn’s cleaning and maintenance, ahead of planning for the next growing season and starting the whole cycle anew.

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