Summer squash and cucumbers can be sown from mid to late spring. Sowing in May is entirely reasonable. I started these a bit early, though, as I often do, in late March. This is only a sensible proposition if the plants can be kept warm and moved on into larger pots as they develop. I keep them in a heated propagator to ensure reasonable night time temperatures, though it always becomes a challenge towards the end of spring to fit in all of the tender plants, especially as they move up to one litre or larger pots.
This year I am growing our old staple, the Striato di Napoli courgette or zucchini, along with a new one for us – Tromba di Albenga. Albenga is in Liguria, Northern Italy, and the source of several interesting local varieties – the oxheart tomato from the region is well known and one we are growing again this year. The Tromba squash forms potentially large fruits, markedly curved, and with bulbous ends that house the seed cavity. They resembled somewhat the old crookneck squash from which the butternuts are descended. This is not surprising as in fact they are more closely related to butternut squash than to zucchini. They can be grown to maturity when the fruits are rather large but are, apparently, more typically used as a summer squash and harvest whilst quite small.
For cucumbers we have three classics: for the greenhouse, Telegraph Improved, and for outdoors the old Long Green Ridge and the somewhat more modern but nonetheless worthy Marketmore.