Staying undercover: How to make the most of a greenhouse
By this point in winter, all I dream of is a greenhouse. Sunny and sheltered, it would let me break all the rules. Heat-loving fare could luxuriate in its extra warmth. All sorts of edibles and ornamentals would grow faster, stronger and fleshier in this see-through sanctuary insulated from the weather outside.
You only have to see the crazily patterned crotons, the flamboyant calatheas, rare orchids and bizarre lilies thriving in public glasshouses in Melbourne and Sydney to know how much you can mash up the seasons.
Greenhouses come in all different shapes and sizes.Credit: Getty
Some of these glasshouses are as grand as ballrooms – and heated for extra effect. They house everything from towering palms to clumping peperomias – they are built for show. But it is also possible to get a greenhouse that is no bigger than a cupboard. Some are even small enough to fit on a balcony, and many are heated by sunlight alone.
The whole premise of a greenhouse is that its transparency allows the sun’s rays to enter and heat whatever is inside – cucumbers in ancient Rome, citrus across Renaissance Italy, ferns in Victorian England and, by the end of next month, the germinating seeds of summer crops for anyone wanting to harvest tomatoes, say, before Christmas.
While greenhouses were traditionally fashioned from glass – hence the term “glasshouse” – they are increasingly being made with clear plastic, which is cheaper, lighter and more easily transportable. They come in all sorts of shapes and sizes, and at a wide range of prices. There are greenhouses that emulate elaborate Victorian designs, ones that take the form of geodesic domes or more minimalist boxes or workaday poly-tunnels. Many look so good they are garden features, as well as growing spaces.
You can also make your own greenhouse with secondhand windows, transparent doors, old fish tanks or any other large pieces of glass or transparent plastic to hand.
The trick is to ensure you provide adequate ventilation because, without good airflow and the ability to release unwanted heat, a greenhouse that is just pleasantly warm in winter can become scorchingly hot in summer.
If your plants are to bask in the warmth of your greenhouse rather than bake in it, sometimes a shading system is required as well. But some greenhouses are so small they can be moved with the seasons, positioned north-south in full sun in the depths of winter and in a cooler, more shady spot in the hottest months.
Access to water is always critical but remember that over-watering can be as problematic as under-watering. Plants should be kept moist rather than all-out wet, which can only encourage fungal diseases.
So, once you have everything in place, what can you do with a greenhouse? For one, you can stretch the growing seasons. Greenhouses allow you to sow seeds earlier in winter and harvest edibles later in autumn.
Herbs, Asian greens and microgreens can be kept in a greenhouse so you have a continuous supply.Credit: Getty
By the end of August you could be sowing seeds of heat loving edibles and flowers that need a soil temperature of at least 20 degrees to germinate. Depending on your climate – and how early you want to sow your seeds – you might also need to place heat mats below the seeding trays. Once the seedlings emerge, however, the warmth of the greenhouse should suffice.
These seedlings can be left to grow healthy and strong before being transplanted outside once the soils have warmed and all risk of frost has passed. More seeds can then be sown in greenhouses – and later transplanted outside – through spring and summer.
In cool areas you might also keep (container-bound) heat-loving produce in greenhouses in late summer and early autumn to ensure conditions are hot enough for long enough for fruits and vegetables to ripen.
While in winter you can farm some crops – herbs, Asian greens and microgreens, for example – in a greenhouse for their entire lifespan thereby ensuring a continuous supply.
Then there are all the ornamentals that you can tend. Plant collectors across the country are cossetting everything from tiny tillandsia seedlings to full-grown vireya rhododendrons undercover in their backyards.
The possibilities are endless. For all our talk about embracing the seasons and planting only what suits the climatic conditions to hand, sometimes you want to grow what would only die outside.
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