Growing under cover extends your season at both ends: you can start seedlings weeks earlier in spring and keep tender crops going later into autumn. A greenhouse gives the most control, but a cold frame or even a run of cloches brings many of the same benefits for far less outlay.
Choosing a structure
- Greenhouse: a glazed, walk-in structure. The most versatile option for raising plants, overwintering tender specimens and growing heat-loving crops like tomatoes.
- Cold frame: a low, lidded box, often against a wall. Ideal for hardening off seedlings and raising early salads and cuttings.
- Cloches and tunnels: portable covers that warm the soil and protect rows of young plants without a permanent structure.
Siting and glazing
Light is everything. Position a greenhouse where it gets sun for most of the day, away from the shade and falling branches of large trees, and sheltered from the strongest winds. An east–west ridge line captures the most winter light if you plan to grow year round.
Glazing comes in three common forms. Horticultural glass is clear and long-lasting but breakable. Toughened glass is safer where children or pets are about. Twin-wall polycarbonate is light, almost unbreakable and insulates better, though it diffuses the view. For an exposed or busy garden, polycarbonate is often the practical choice.
Ventilation matters more than heat
The most common mistake is too little ventilation. On a sunny day a closed greenhouse can overheat within an hour, cooking seedlings and encouraging disease. You want roof vents and side or louvre vents so air can flow through. An automatic vent opener — a simple wax cylinder that expands with heat — opens and closes the roof vent for you and is one of the best small investments you can make.
In summer, shading paint or netting and a damp floor ("damping down") keep temperatures and humidity in a workable range. In winter, bubble insulation and a frost-watch heater protect tender plants without heating the whole space.
Using the space through the year
- Late winter to spring: sow seeds and raise seedlings in the warmth, then harden them off in a cold frame before planting out.
- Summer: grow tomatoes, peppers, cucumbers and other heat-lovers in the ground or in pots, ventilating and watering generously.
- Autumn: extend salads and herbs, ripen the last fruit, and bring in tender plants before the first frost.
- Winter: overwinter tender specimens, force early bulbs, and keep hardy cuttings ticking over.
Hygiene and watering
Warmth and shelter help pests and diseases as much as plants, so keep the greenhouse clean: remove dead leaves, wash the glass each winter to let in light, and space plants for airflow. Water in the morning so foliage dries by nightfall, and consider capillary matting or a simple drip line to keep pots evenly moist while you are away.
Start small
If a full greenhouse feels like a big step, begin with a cold frame or a few cloches for a season. You will learn how protected growing changes your timings and what you most want to grow, which makes choosing a larger structure later a far easier decision.