With temperatures rising and summer just around the corner the unheated greenhouse can really start to earn it’s keep. Whilst there are a huge range of vegetables that thrive outdoors in our climate, there are also a select few that really do need the protection of glass in order to give their best.

Tomatoes.

The most obvious and perhaps even traditional of these are undoubtedly tomatoes. There are now a vast array of varieties and types of tomatoes available for the home grower, some of which can be successfully cropped outdoors if the weather is kind. Down here in “sunny” Devon the last two summers of eternal wetness have well and truly put paid to any attempts to produce outdoor tomato crops, with most plants succumbing to blight and weather-related fungal attacks  long before they were able to set fruit.

For those plants grown under glass, though, the outcome was much happier, and although 2008/2009 will certainly not go down in any veg growers record book some decent crops were eventually produced despite the cold temperatures and general lack of anything resembling a traditional summer.

The upright, cordon tomato varieties such as ‘Sunbaby’ and ‘Shirley’ should be selected for greenhouse use. Seeds should be sown in mid-March, with the subsequent seedlings being ready to transplant in mid-May. There are also many outlets for young plug and seedling plants which will perform equally admirably and which allow you to catch up if you didn’t have a chance to start from seed earlier in Spring.

Transplant seedlings into 12 inch pots with a rich, free draining compost, and make sure to include a tall cane or other support for each of the plants. Given a little care, plus lots of water and tomato feed, the extra heat afforded the plants under glass will produce much higher yields of fruit, with much better ripening than would be the case outdoors.

Cucumbers.

The range of cucumbers for home growing has expanded considerably in recent years with the arrival of a range of easily obtainable F1 hybrid varieties (such as ‘Fernspot F1′) that are easily grown and produce consistently good results.

Care is pretty much as for tomato plants, with seeds sown in March and seedlings or plugs transplanted into 12 inch pots in mid-May.

The wild plants from which cucumbers have been developed are trailing, rather than climbing, but the fruit ripens far more successfully with good access to light and air, so plants should be supported with canes or tied into wires that run along the length of the greenhouse.

Once the first half-dozen leaves have appeared on the young plants the growing tip should be pinched out to encourage the production of several growing shoots.

Cucumber plants are only weakly twining at best and obviously carry very heavy fruit, so it’s particularly important that these developing shoots are carefully tied in to their supports to keep them upright and stable. Plants should be kept well watered and a rich tomato-type feed given every two weeks.

Aubergines.

Far less commonly grown in this country, aubergines, like tomatoes, are South American members of the nightshade family that most definitely need the extra heat and protection from wind that a greenhouse can provide. As with cucumbers, much work has been done to develop varieties that can be easily grown at home, and very heavy fruiting varieties like ‘Moneymaker’ make for easy and extremely rewarding  greenhouse crops. The plants are also very attractive, not just for the rather spectacular fruit, but also the for the foliage and large purple flowers.

Aubergines should be sown indoors or under heat in March or in an unheated greenhouse in April. Once they have produced four leaves – any time from mid-May to mid-June, depending on when they were started – they can be pricked out and transplanted into 9 inch pots, together with the same staking/support as for tomatoes and cucumbers.

Plants should not be allowed to develop lots of small fruits or none will be able to ripen properly. Each plant is capable or maturing anywhere from three to six fruit in a growing season – depending on how warm and sunny the summer turns out to be - so pinch out any weak or poorly developed fruit-lets to let the plants divert energy into a few really good ones instead. Lots of water and regular supplies of tomato feed will, once again, ensure the best crops.

Capsicum.

Saving the best to last, we come to the real hot-house gems, the Capsicums or peppers. Until fairly recently hardly anyone grew these South-American beauties in their home greenhouses in this country, but now they are very much the “vegetable de jour” and plug plants are almost as readily available as tomatoes and cucumbers.

Capsicum plants are somewhat more tender than toms, cus and aubergines, particularly when first germinated. Seed should only be sown under glass when temperatures are remaining consistently above 12C, and the seedlings (or bought-in plugs) transplanted into 8 inch pots once they have developed three of four true leaves.

Capsicum are not true climbing plants, but, rather like cucumbers, they certainly do require additional support of a short cane etc., in order to successfully bear their large fruit. The plants should be shaded from mid-day sun and kept slightly on the dry side, without actually ever quite drying out completely. A half-strength tomato feed should be applied every two weeks once the plants are growing strongly.

There are now a wide array of Capsicum varieties available to the gardener, from the sweet bell peppers that start out green and ripen to yellow, orange, red or black/purple (like the fabulous ‘Tequila’), to the smaller, much hotter chillies than all turn scarlet upon ripening – they are all part of the same Mexican species: Capsicum annuum.

Aside from the obvious culinary uses Capsicum are such beautiful fruiting plants that you’ll be continually admiring their progress. Personally I can’t think of any more rewarding use for your greenhouse space this summer.