If you want to sow seeds earlier, have better crops of tomatoes and cucumbers, and tender plants during the cooler months, buy a greenhouse.

Ilkley-born TV gardening guru Alan Titchmarsh loves pottering in his greenhouse, which measures 8ft x 15ft, but advises green-fingered enthusiasts to think carefully about their needs before they buy.

“Make it twice as big as you think you need, because however big a greenhouse you get, you will fill it to overflowing. Buy the largest you can afford and fit in,” he says.

Don’t forget to allow for hidden costs of a greenhouse, Alan advises. Installing electricity and water will make a dent in your budget, along with laying a path to the greenhouse. Staging, propagators, watering systems, automatic vent openers, blinds, heaters and insulation will also rack up the costs.

A heated greenhouse will give you a much bigger range of plants to grow, Alan explains.

“Try to get your heating sorted; make it electric heating which is thermostatically-controlled so you can save money. Even being able to keep the frost out will widen the range of plants you can grow in there.”

Fan heaters move the air around and will heat a larger area efficiently, while tubular heaters are suitable for smaller spaces.

Invest in a maximum/minimum thermometer and put it where it will be easily read, but out of direct sun.

“An unheated greenhouse limits your season from April to September, although you can put hardy shrubs, flowering currants and camellias in pots if it’s unheated,” says Alan.

The greenhouse should be in full sun; if it’s shady, the plants tend to become leggy. Place it in the most open site you can, around 10m (30ft) from any big trees. As well as the shade they cast, falling leaves and twigs will block gutters and increase the frequency with which you have to clean the glass.

“You can potter in the greenhouse all year but there will come that hard core of winter from November to February when it’s quiet, although my own greenhouse has been full of scented leaf pelargoniums right the way through.”

To grow ornamentals in your greenhouse, work out what temperature you can keep the greenhouse at and grow plants that suit that environment, rather than trying to match the heat to the needs of plants.

To keep an unheated greenhouse looking good, grow a succession of flowers, which will mean encouraging some plants to bloom earlier than normal.

Scented shrubs are great early flowerers. The hardy Daphne odora Aureomarginata has purple-pink fragrant flowers naturally early in the year and even earlier if under cover.

A greenhouse will allow you to experiment with seeds, grow more fruit and veg, take cuttings and widen the range of plants you grow.