It’s the time of year for seedlings, cuttings, chitting and propagation, but our temperamental weather means you can’t guarantee when that last frost will be. A greenhouse will extend your growing season, protect seedlings from bad weather and provide a safe haven in coming winters for tender plants. Our guide to choosing, filling and accessorising your greenhouse starts here.
The size of your greenhouse will depend on where in your garden you’re going to put it. In an ideal world, it will get uninterrupted sun throughout the day with one long side facing south. If you choose to lay a concrete base for the greenhouse to sit on, paving slabs work perfectly and are easy to do yourself. Make the base slightly bigger than the greenhouse footprint and if you want border soil in addition to grow bags and pots, you will need to plan that now. Be careful of locating your greenhouse under trees as falling leaves will block light.
Glazing to ground level is the most common greenhouse structure, but half-walling with masonry or timber does reduce heat loss. Aluminium frames are long lasting and hassle-free but if you want the beauty of wood, go for a good treated hardwood. The taller the construct, the more light is transmitted, and it’s better for your posture too!
Glass transmits and holds more light than plastic, although polycarbonate plastic glazing, while expensive, is durable and does hold heat well. Glass comes in two forms; horticultural and toughened. Horticultural glass is cheaper but shatters into unpredictable shards, while toughened is designed to disintegrate into tiny particles for safety.
Ventilation is probably the most vital aspect of successful growing. Good ventilation keeps fungal diseases at bay, so make sure your greenhouse has multiple vents, in the roof and on the sides. Many greenhouses come with integral guttering to capture rainwater. Keeping a water butt and/or watering cans in the greenhouse will keep the water at an ambient temperature – you can shock plants with cold water.
Your choices are grow bags, pots and/or border soil. All soil needs replenishing to keep diseases at bay and keep in mind that this is much easier to achieve with pots and grow bags. Staging and shelving, whether one-, two- or three-tiered, is really useful along least one side of the greenhouse. You should always leave one area clear of seedlings and plants as a good gardening worktop for you, and have designated areas for storage.
While the glazing aspect of a greenhouse amplifies heat, in very cold winters you may need to use bubble insulation on the interior to protect from frost. If you want to install electric heating for cold winter growing, then to save money, locate your greenhouse as close as possible to the house. Conversely, on a super-hot summer’s day, a little shade netting will do wonders for your plants’ health. Have a thermometer with minimum and maximum readings to best moderate your temperatures and you may also want to hang some fly screens to combat flying pests and foraging robins!
If you have restricted space, you might want to consider a lean-to greenhouse. It’s really got to be placed on a south facing wall as the light levels are so much lower. The back wall retains heat though and is often trellised for climbing plants. Another good small garden solution is a small tent-like plastic greenhouse, great for raising seedlings.