Gardening tips for mid May

Penstemons

Of course, it s preferable to have permanent planting in your herbaceous borders, but inevitably there ll be gaps. Bedding plants are an obvious fill-in, but what about using penstemons? You can easily get them at plant centres during the growing season. And although they re more expensive than bedding plants, they can be propagated and used for many years. For the best results, treat them as annuals, buying them now and planting straight out where required. New ones make stronger plants and we find they flower better than last year s that we ve left in the borders. Penstemons are softwood plants, so they root very quickly. Later on, take cuttings in the early autumn, pot them on and over-winter in a cold greenhouse. This ll keep them safe, as some penstemons are prone to frost damage.

Tomatoes

Now is a good time to plant your tomatoes in an unheated greenhouse. We use Grow Pots (available from good garden catalogues) they re designed to be used with grow-bags, which prevent the problems associated with growing tomatoes in the soil of greenhouse beds. Made of ridged plastic, the serrated base of a Grow Pot cuts the correct size hole in the grow-bag; once it s in place, set the plants in the inner ring with extra compost. When needed, you can trickle liquid feed into the inner ring where the plant is growing; the outer ring is used for general watering, soaking the grow-bag through the holes in the base. This way, the amount of water can be controlled in the early stages of the plant s growth. Grow Pots are a good investment, as they can be used for many years.

Peas

Peas sown now should be ready to harvest in August, but they need attention. First, ground conditions mustn t be wet and cold, and secondly, once they start coming through, you ll need to protect them from the pigeons and partridges. Thirdly, most varieties need support and quite a lot of room, which puts off those with smaller gardens from growing them.Sow three rows of peas in a trench 6in wide and 2in deep; the width between rows depends on the height of your variety. Support them as soon as they come through, as it gets much more difficult later. Mulching between the rows helps keep weeds under control. To get their maximum sweetness and flavour, you should cook your peas within an hour of picking, so the sugars don t turn to starch.

Sweetcorn

Sweetcorn started in pots earlier this year can now be planted out, if there s no risk of frost. Plant a little deeper than the surface of the pot, to help the corn grow roots up the stem and anchor itself to prevent wind damage. Plant in blocks for increased pollination and consider a mulch between plants to conserve moisture. I underplant with trailing nasturtiums, which you can still sow indoors now to speed up germination. Plant out between the sweetcorn as soon as they are large enough.

Philip Maddison is head gardener at Harrington Hall, Lincolnshire (www.harringtonhallgardens.co.uk)