Garden Notes for May 2026.

May is always such a hopeful month, but don’t be fooled by all the half-hardy bedding plants that will be offered temptingly. It is not safe to plant them outdoors. Even if plants like geraniums, salvias, lobelia, marigolds and so on are not killed by a late frost, they can still receive such a severe check from cold May nights that they never completely recover to give a proper display.

But don’t let that put you off getting in stock where you can give it some protection in a cold frame or greenhouse. Use of garden fleece at night will also be just sufficient to keep off the worst falls in temperature and will help to harden off the plants in time for June when they can be planted out.

Go along to the Horticultural Society Plant Sale on Saturday 9 May, the doors open at 10 am. Previous experience has shown that it is very much the case that the Early Bird gets the best bargains, although we do try to keep a flow of plants going. It is surprising how there is a varied demand each year, we try to keep a good selection, but we can never quite predict what will go well and what will stay behind!

Sweet peas should be tied in regularly, especially if you are trying to grow large blooms, as you will be taking out the side shoots so that all the growth goes into the tip. They can be fertilised; use one that has a low nitrogen content as too much may increase bud dropping.

As alpine plants in the rock garden finish flowering, trim back the growth to keep the plants neat and compact. By doing this you will encourage them to make good growth for flowering next spring. In the same way flowering shrubs like philadelphus, deutzias and escallonias can be pruned as soon as their flowers fade to encourage new growth.

Keep up succession sowings of lettuces and peas. Runner beans and zucchini should be sown early on. Because our garden is a veritable slug and snail city (we have a lovely lot of thrushes who help keep the snails under control) we generally start our runner beans in the greenhouse and plant them out at the end of the month. To give runners the best chance, sow them individually in the divided plastic trays (24 to a seed tray). Try to get the beans out before they start shooting too much and become tangled up with each other.

All tall flowering plants like delphinium, gladioli, even some of the carnations will need to be staked, as they really do need support when they are in full flower.

Put clean straw, or black plastic under strawberry plants to keep the berries clean and protected.