Spring arrives in the greenhouse long before it makes its presence felt in the rest of the garden. By March many plants will be busily putting on new growth but, at the same time, these rising temperatures also bring the renewed threat of pests, as they too begin to warm up again. The spring greenhouse is a hive of activity in more ways than one – and a few routine tasks now should set things up for the rest of the year.
Preparing the Greenhouse
Once the threat of cold weather is gone, winter insulation can be taken down, but the changeable nature of the season inevitably means that you will always need to keep a weather eye open and be ready to provide warmth – or conversely shading – as circumstances dictate.
As it becomes warmer through the spring, watering should be increased, the plants fed more frequently – rising from fortnightly in March, to weekly towards the end of May – and the humidity also raised.
For most parts of Britain, shading will need to be in place from around the end of April or early May – perhaps a little later in the far north. It is important to keep the greenhouse well ventilated throughout the spring, particularly as you begin watering more, to guard against mould or mildew problems. However, you need to make sure that on windy days, the breeze does not simply blow straight through and chill everything down, something tender shoots and seedlings will not tolerate.
Planting and Propagation
By the middle of March, most seeds – including tomatoes and beans – can now be safely sown even in unheated greenhouses and it is a good opportunity to pot-on any potted plants which have grown too large. It is also the time for taking cuttings of the likes of fuchsias, pelargoniums and chrysanthemums and if the greenhouse grows peaches, by the end of this month they will be in flower and in need of pollinating if they are to produce a crop later in the year. Once seedlings become large enough, prick them out and pot them on – along with any rooted cuttings or other young plants as they grow.
In April, half-hardy plants which have been over-wintered in the greenhouse should be moved into a cold frame, or some other suitably sheltered spot, to begin hardening them off for planting later – remembering to protect them from the attentions of slugs and snails. This also frees up some space to begin sowing melons, marrows or summer rockery plants at the end of the month.
As a final April task, Maidenhair ferns need cutting back, dividing and re-potting and other varieties of ornamental ferns can now be potted-on. Softwood cuttings of perennials can be taken in May and in milder parts of the country, vegetables and half-hardy ornamental plants raised under glass can now be hardened-off and planted-out in the garden.
In the greenhouse itself, fruit and vegetable plants will now be in need of a little attention to ensure a successful harvest. The side-shoots of tomatoes should be removed to concentrate the growth in the fruiting tips and young aubergine or pepper plants which have reached around four or five inches (10-12 cm) tall need to be transplanted to their final position and taller varieties given suitable support.
May is also a good time to do a little forward planning for the other end of the year. Towards the end of the month, taking cuttings of geraniums will provide autumn colour and sowing cineraria seeds will give the promise of indoor flowers from December onwards.
Spring is a busy time in the greenhouse and largely sets the scene for the whole of the coming growing season. With so many young, vulnerable plants growing in close proximity, there is a real danger of disease or pests, making it vitally important to remain ever-vigilant for the tell-tale first signs – and to be as clean and tidy as possible to reduce the risk. However, with a little care, it should be possible to enjoy the start of the new growing season without major mishap and look forward to the promise of the summer ahead.