Sow seeds of fast-growing hardy annuals, such as Eschscholzia (California poppy) or poached-egg plant, to fill gaps. Click here to visit our Seeds & Propagation page.

Now is also the perfect time to plant perennials. These delightful plants give excellent value for money, flowering year after year and can also be divided to make more plants as they grow. Click here to visit our garden perennials page.

Plant up hanging baskets, and leave them in a sheltered spot before hanging fully outside.

Begin planting summer bedding in the last week of May as long as there is no forecast of frost. An hour before planting water the plants in their containers and remember to water after planting. Click here to visit our Bedding Plants page.

Spring is also the ideal time to plant shrubs as the soil is moist and warm enough for new root growth to help the plants become established quickly. Click here to visit our Shrubs page.

Apply shade paint to the outside of the glass or use blinds on sunny days to prevent temperatures from soaring.

Open doors and vent on greenhouses to increase ventilation on warm, sunny days.

Damp down the floor of the greenhouse regularly on hot days, to increase humidity levels.  This benefits plant growth and also reduces the risk of pest problems such as glasshouse red spider mite.

Don’t forget to give greenhouse plants more space as they put on new growth.  This will help to prevent disease and to contain early pest infestations.

Harden off your half-hardy bedding plants that were started off early under cover.  By placing them outside for a short period only at the warmest time of day and then gradually increasing the length of time they are outside you can avoid the ‘shock’ that they otherwise experience when moved outside suddenly and permanently.

Check plants at least every few days to see if they need watering.  Seedlings will need daily attention.  Use rain, grey or recycled water wherever possible.

Continue to prick out and pot on new seedlings and cuttings.

Hydrangeas and fuchsias can be propagated from softwood stem tip cuttings.

Regularly inspect plants and also the structures of the greenhouse and conservatory for glasshouse red spider mite, whitefly, thrips and other pests. Paying careful attention to the undersides of the leaves and to each plant in turn can spot early infestations that would otherwise be missed. Control with approved treatments and hang yellow sticky traps to help monitor numbers of flying pests.

Check roses for signs of blackspot (left), aphids and leaf-rolling sawfly damage.

Damp down the floor of the glasshouse regularly on hot days to reduce the risk of glasshouse red spider mite.

Brush up fallen compost and debris and pick off dead leaves from plants. This will help prevent pests and disease spreading.

Inspect lilies for red lily beetles as the larvae can strip plants in days.

Vine weevil larvae can be a serious pest of containerised plants and become active this month. Tip out the rootball of suspect plants and inspect for the creamy orange-headed maggots which tend to curl up into a ‘C’ shape. There are various chemical and biological controls available.

Aphids can multiply rapidly during mild spells. Remove early infestations by hand to prevent the problem getting out of hand. Protect sweet pea plants in particular, as they can get sweet pea viruses.

Click here to visit your Pest, Weed & Fungal Control page.

Early May – sow (under cover) beans, marrows courgettes and squashes, two per pot, and thin out the weakest seedling to leave the strongest plant.

Early to mid May – sow seeds of herbs, such as parsley, chives, coriander, garlic, basil, dill, fennel, mint, thyme, sage and lovage.

Late May – sow beetroot, lettuce, watercress, rocket, radish, spring onions, coriander, parsley, chives, carrots, swedes, turnip, leaf beet, spinach, cabbage, peas and mangetout, endive, marrows and courgettes, turnips and chicory. Sow a few seeds of salad leaves and stir-fry leaf crops every two to three weeks to ensure a regular supply.

Sweetcorn, courgettes, marrows, pumpkins, cucumbers, tomatoes, French beans and Runner beans are temperature sensitive crops. If they are sown in soil that is too cold, germination will be poor and any seedlings that do appear will not crop as well as those started in warmer soils. The critical period is when the seeds are taking up water in order to start the germination process. Once this is complete, lower temperatures are acceptable.

No time to sow – Click here to view our vegetable plants page.