Success with greenhouse growing
Alan Titchmarsh shares his advice for getting the most out of your greenhouse, so you can enjoy growing all year-round, whatever the weather
Alan shares tips on getting the most from the gardener’s glassy sanctuary
A greenhouse is something of a sanctuary for the gardener – a place to be enjoyed in all weathers
To call a greenhouse ‘ the cathedral of the garden’ might be stretching things a bit. After all, a 6ft by 8ft glass box is a far cry from Westminster Abbey. But there is something about even the smallest of greenhouses that offers a kind of hallowed atmosphere. It becomes not simply a place to grow plants that would otherwise fail to thrive out in the open, but also something of a sanctuary for the gardener – a space to be enjoyed in all weathers, and an opportunity to grow tomatoes, peppers cucumbers and aubergines, as well as exotic ornamental plants, and you don’t need to run up a heating bill that would make a Russian oligarch blench. If you long for tomatoes weeks before they are ready in the garden, or if you want to overwinter tender pelargoniums and other bright-flowered plants; if you fancy col lecting cacti, succulents, streptocarpus or tender fuchsias; if you yearn for cucumbers and melons at your bidding, or a grapevine yielding succulent fruits, then a greenhouse is a must. In colder parts of the country, a greenhouse is even more valuable than in the milder south, as it will extend your growing season. It will allow you to start plants – such as dahlias, tender vegetable seedlings and bedding plugs – into growth earlier than they could be risked outdoors. It will also prolong the growing season when the nights turn chilly. A greenhouse also enables you to grow a host of exotic plants that might otherwise be off limits, for example, citrus fruits and banana plant s can be overwintered under cover and put out in summer. Under the covering of glass – even if it is kept just frost free – a part of your garden is opened up for year-round use and entertainment.
Setting the stage
If you want to grow lettuces and tomatoes in a soil border, leave one side of the greenhouse with its earth exposed. Alternatively, staging can be run all round the greenhouse. It is certainly worth investing in sturdy staging (waisthigh shelving) down one side of the greenhouse so that pot plants can be easily tended to. If you are planning to display the likes of pelargoniums, fuchsias, schizanthus and streptocarpus, then tiered staging will give you a waterfall effect of foliage and flowers. If you plan on growing a grapevine, the
The more ventilators a greenhouse has, the happier the plants
roots can be planted in the soil and the stem led up behind the staging, with the vine stems ( rods) slung from the glazing bars above. In my own greenhouse, I have staging all round so that tomatoes and cucumbers can be grown in large pots or growing bags placed on it. A shelf underneath the staging, where the light levels are lower, is a great spot for maidenhair ferns, which enjoy shade and humidity. Make sure that plants that demand plenty of sunlight are put where they will receive it – on shelves nearest the glass.
Ventilation and watering
In your excitement about having somewhere warm to work in winter, don’t forget the importance of ventilation, for in summer the greenhouse will turn into a furnace without adequate air circulation. The door can be opened, but high-level (ridge) and lower (eaves) ventilators are vital to ensure that temperatures can be kept at an acceptable level and that humidity can be controlled by a healthy flow of air. The more ventilators a greenhouse has, the happier the plants – and the gardener. If you are out at work all day, automatic ventilating arms can be fitted to open the vents when the temperature rises above a certain point. They are wonderful life- savers for plants grown by gardeners who can’t be in attendance all the time. Shading, too, is vital between May and September to prevent plants from being scorched by the magnified effect of the sun. When it comes to watering, a tap installed inside the greenhouse will save you a lot of lugging a hosepipe or watering can up and down the garden. Automatic watering systems are now available at reasonable cost and can be rigged up to a small batteryoperated computer fitted to the tap. When you are absent for long periods of time they can be a useful alternative to trying to find a helpful neighbour who knows how and when to water plants.
Electricity is by far the most efficient way of heating a greenhouse, since it offers dry, controllable heat. There are lots of greenhouse heaters that are fitted with thermostats to ensure efficiency and economy. But don’t under any circumstances use a domestic heater in the greenhouse. It won’t be safe for use where water is around and in ext reme circumstances may even prove lethal. Unless you want to grow tropical plants in winter you won’t need to heat your
greenhouse to a high temperature. Most plants – such as citrus, pelargoniums and tender fuchsias – will be happy if the temperature doesn’t drop below 7°C (45°F), though if you can keep them a little warmer than this they will continue growing. Freedom from frost is critical – unheated greenhouses are useful in spring for the shelter they provide but in the dead of winter they offer little useful protection.
While a greenhouse has many advantages, it has its own range of pests – red spider mite, mealy bug, whitefly, vine weevil and scale insects. These can be controlled with bought predators and, in the confines of a greenhouse, this biological control is usually more effective than it is outdoors. When it comes to diseases such as mildew and botrytis, adequate air circulation will
keep such outbreaks to a minimum. Removing dead leaves and flowers from plants will help and is a routine that every greenhouse gardener gets into the way of. For me, it’s one of the joys of my morning! Turn over for our greenhouse buyer’s guide
September 2017 gardenersworld.com
Greenhouse conditions are ideal for onion storage in winter