Courgettes, cucumbers, squash and cucamelons are generous plants and often reward you with a bigger harvest than you can handle.

Though cucumbers originate from India and squashes from Central America, here we lump them all together and treat them in much the same way. The vegetables are all tender and need fertile soil butthere is such a wide selection of new varieties and old favourites that you need to choose carefully.

Wherever you plant – in a polytunnel, a greenhouse or outdoors – deciding when to buy these cucurbits is critical, and this depends on where you live. Gardening at 200 metres above sea level, I could get a frost any time in May, and possibly into June, but those of you in Glasgow and the west coast are normally two or three weeks ahead of me.

Confusingly, many of these tender plants appear in some garden centres before it’s safe to plant them out. But if you delay buying, the plants could be sold or past their best. It’s safest to buy what you want, repot in a larger container and protect it until all risk of frost has passed.

Though all cucurbits are frost tender, courgettes and squashes thrive outdoors throughout Scotland. In a well-protected, sunny spot in the garden you might succeed with cucumbers and cucamelons, but a polytunnel or a greenhouse is safer.

When skimming through seed catalogues, I’m always surprised that the young plants are often sold in packs of three or even six, when one or two courgettes or cucumbers are ample. When buying, have a clear idea not only of the space you have but also how many fruits you can handle. If you only need one courgette make sure it is a variety such as Partenon that doesn’t need pollination.

Plant breeders have developed varieties to fit any space in the garden or patio. Traditional courgettes and squashes are greedy and devour a full square metre of ground. At the centre, dig a 30cm square hole, one spit deep; add equal amounts of mature compost to excavated soil; refill the hole; cover it with a permeable membrane and plant through a slit in the membrane. For better results, warm up the soil by putting a generous amount of fresh horse manure or grass clippings into the hole and cover with the soil and compost mix as above.

Small growing varieties are also suitable for 20-30 litre containers. These include the courgette Delistar and the cucumber Patio Star. These are grafted plants, a technique that was launched last year. This is where a successful and tasty variety is grafted on to the rootstock of a tougher variety, rather like apples and pears. They reputedly grow more successfully and resist soil pathogens.

It’s well known that male cucumber flowers can cause indigestible, bitter fruits if allowed to pollinate female flowers. Victorian gentlemen were well aware of this, and steadfastly refused to eat raw cucumber sandwiches. After all, a bout of unseemly belching could steal up on an unwary consumer.

Fortunately, burpless varieties were developed to protect these anxious gents. And modern, non-bitter varieties are now readily available, including Rocky, with truly delicious small fruits.

Every courgette and squash should grow well, but cucumbers can sometimes suffer from stem rot, a fungal infection that destroys the base of the stem. I always grow two plants, just in case (see panel).

As I mentioned a couple of years ago, cucamelons, Melothria scabra, make an unusual and tasty addition to cucurbits. Grow them once and you’re hooked for life. This Mexican plant needs the warmth of a greenhouse or polytunnel to thrive. And, despite looking fragile, it vigorously scales a frame like a cucumber and produces a mountain of tiny, grape-sized fruits. This nibbler’s paradise tastes like cucumber, infused with a refreshing hit of lime. A bit of grazing accompanies every visit to the tunnel.