If you have viburnum tinus or viburnum opulus shrubs in your garden, check for signs of viburnum beetle grubs. The grubs start nibbling holes in the leaves this month, giving plants a very tattered and untidy appearance. Spray any infected plants with Bug Clear Ultra now, and repeat again in three weeks.
Feed established lawns if they are lacking in colour and vigour. Check for signs of weeds and moss and consider applying a combined feed, weed and moss killer such as Evergreen Complete.
Remove dead and fading flowers from tulips and daffodils, and apply a liquid fertilizer such as liquid seaweed with iron to the foliage. This will encourage more flowers next spring and help prevent daffodil blindness.
Check established houseplants showing signs of being root bound, and re-pot if required. Use houseplant compost for most plants, but choose specific compost for orchids and ericaceous compost for acid-loving plants such as azaleas and gardenias. If in doubt, ask your local garden centre.
Make regular sowings and plantings of salad crops and protect against late frosts, delay planting out tender plants such as tomatoes, cucumbers etc. until early June.
Feed new and established roses, and regularly inspect them for any signs of aphids and blackspot. Spray them if necessary with a combined insecticide and fungicide such as Rose Clear Ultra.
Check for any signs of slug damage on newly emerging foliage of perennials and seedlings – not just plants growing in the garden, but those in patio pots and containers too. Slugs can be prevented and controlled with organic pellets, nematodes and non-chemical traps.
Remove wallflowers and other winter-flowering bedding plants to make room for summer and autumn-flowering bedding. You can improve soil in advance by adding organic compost and a controlled-release fertilizer.
Sowing new lawns, or over-seeding dead or bare patches, can still be carried out during May. Choose the right grass seed for the job – there are special mixtures for shade, multipurpose, hardwearing or extra fine. Don’t walk over or mow newly sown grass until it is 5 – 7.5cm tall (2 – 3″), then lightly trim at the highest blade setting.
Plant out sweet pea seedlings, making sure that tall-growing varieties have canes, trellis, netting or an obelisk to climb up. Keep plants well-watered during dry weather and feed them regularly with a liquid plant food to encourage good growth and masses of flowers.
Broad beans should have their tops pinched out, once around five trusses of flowers have formed, otherwise they can become infested with blackfly. Support tall, unstable plants with canes.
Hanging baskets of frost-tender plants can be planted up in a greenhouse or conservatory and grown on under cover until next month. A wonderful selection of pre-germinated seedlings and plug plants are available now – plant them in potting compost containing a moisture-retaining gel.
Carefully remove the blossom from newly-planted fruit trees to give them every chance to get properly established before bearing fruit, and keep them well-watered during dry weather.
Check all lilies for any signs of the Scarlet Lily Beetle – the larvae can strip plants in days, making them look very untidy. Spray with Westland Resolva bug killer, or remove any beetles by hand.
Plant new pot-grown roses – prepare the ground in the planting positions with compost and fertilizer, and plant at the same depth as the pot. If you’re planting into pots, use a soil-based compost such as John Innes No3.
Direct sow seeds of half-hardy annuals such as cornflowers, Californian poppies, nigella and night scented stocks for an easy, colourful display this summer.
Don’t be tempted to cut down or tie up the foliage of spring flowering bulbs. Let them die back naturally – cutting back can lead to blind bulbs next season.
Keep on top of all weeds throughout the garden by regularly hoeing, careful use of chemical weed-killers, or applying a good mulch of composted bark.
Until you’re certain that the last frost has passed and the nights aren’t too cold, continue hardening off bedding plants and frost-tender vegetables by standing them outside on fine days and returning them to the greenhouse or cold frame at night.
Plant new hardy perennials – a vast range of pot grown plants is now available. Plant into well-prepared soil and keep them well-watered during dry weather.
A fortnight after planting tomatoes, cucumbers etc in the greenhouse, start feeding every two weeks with a liquid tomato food. They’ll grow very fast, so tie them into canes or strings regularly, and remove side shoots on cordon-grown plants.
One thing to watch out for in tubs and troughs that are standing on the ground is ants. Ants can be quite serious when they nest in containers. They don’t attack the plants directly – instead they excavate the compost from inside the pots, so the roots of the plants can’t take up any water and they die of thirst. Apply ant powder or gel if required.
Before pruning or trimming shrubs or hedges, check for any signs of nesting birds. If you’re lucky enough to find a nest, leave the pruning until later when the birds have fledged.
Regularly feed and water all plants growing in patio pots and containers, and place a plant saucer under pots to help reduce water loss. Established pots may also require a top-up with new compost.