May in the garden

In May the days are longer and warmer, hopefully the risk of frost will have passed by the end of the month, and there is plenty to do in the garden, greenhouse and vegetable plot. You'll want to start tidying and cutting back your spring plants, planting out flowers and veg for summer and preparing for autumn – sowing seeds and planting out chrysanths.

The cutting garden

Sowing & growing

Sow an annual meadow. Choose an area in a sunny spot, with well-drained soil. Clear, dig over and rake to form a fine seedbed. Keep an eye out for weeds but otherwise leave alone – no thinning, no staking. If there is no rain for two weeks, water again with a deluge to encourage germination.
Once the frosts are over, plant out hardened off half-hardy annuals.
Thin hardy annuals in seed beds, to make ready for planting out.
Sow some fast-growing annuals to fill in gaps that may appear later in the season.
Direct sow zinnias.
Do a second sowing of half-hardy annuals inside, eg antirrhinums, amaranthus, and Moluccella laevis (Bells of Ireland), to give you flowers until nearly Christmas.
Sow biennials, eg foxgloves, honesty and wallflowers.
Harvest seed of cowslips and primroses before it drops, and sow straight into a seed tray. Put this somewhere cool and keep it well watered. They might not germinate until the autumn, so don’t forget to water.

Bulbs & tubers

Once spring bulbs are over, rather than cutting down the foliage, leave to die and break down naturally. Doing this and adding liquid fertiliser around the clumps will encourage strong growth next spring. It’s still an idea to deadhead any faded flowers to prevent plants wasting energy creating seed heads.
Start successional planting of gladiolus bulbs.
Lift and divide bluebells when they start going over. Transplanted in the green, still in active growth, their roots settle in quickly. Remove flower heads.
Deadhead and top-dress late varieties of tulips such as 'Orange Favourite' and 'Double Maureen' with blood, fish and bone. This encourages them to grow well until their leaves die right back, photosynthesising enough to store starch in the bulb for a good show next year.

Harvesting

Lovely things to pick and arrange from your garden in April:

Bulbs: Narcissi, fritillaries, hyacinths, tulips, alliums
Hardy annuals: Euphorbia oblongata, first autumn-sown marigolds
Perennials: Euphorbias, polyanthus, hellebores and first Solomon seal and lily of the valley

Many tulips are looking at their best now. They continue to grow once you’ve cut them, as the main growth plate is just below the flower head. With the heavy-headed parrots, whose heads tend to droop after a day or two in, push a darning needle through the stem just below the head. This disrupts the growth plate and hence slows cellular division and the droopy-head syndrome.

Cut plenty of alliums for a vase – they're at their peak of flowering. Add a drop of bleach or slosh of vinegar to the flower water. This stops bacterial build-up and slows the stem ageing, and hence reduces any oniony smell.

Perennials, shrubs & trees

Pruning & tidying

Do the “Chelsea chop” – it's time to take the secateurs to later-flowering herbaceous perennials. Prune about a third of the stems by a third, another third by two thirds. This delays flowering in those stems, and increases the overall flowering season.
Cut back allium foliage – it's looking pretty messy by now and can be removed without affecting the bulb.
Spring flowering shrubs should also be pruned back to encourage next year’s growth, and now is also a good time to give any box and other formal hedging a bit of a gentle tidy up. Make sure to use hand shears rather than mechanical hedge trimmers which often bruise rather than cut the leaves.
Tie in sweet peas as they're starting to romp away, so aim to do this once every 10 days at least from now on, right through the growing season. If you encourage them to grow vertically, their flower stems will be straight and you’ll get better flower production.
Plants such as aubretia and alyssum can be cut back after flowering to encourage new growth and possibly more flowers.
Trim early-flowering clematis once they have finished flowering. Cut them back if they have filled their allotted space. They don’t need pruning, but will get dense and matted without.
Tie in late-flowering clematis varieties.
Continue to divide congested perennials and keep on top of weeding.
Cut all the old shoots back on your penstemons to just above where there is new growth at the bottom of the plant. If there are no new shoots at the base, cut just above the lowest set of leaves.

Planting

Plant out dahlia tubers and chrysanthemums for late summer-autumn flowers.
Climbers can make wonderful patio displays in the right pots. Make sure any pots you use for this have a diameter of at least 35cm to give the climber roots enough space. I love the rustic effect of making wigwams from silver birch, but if you’re after a more regimented look, canes will do the job just as well. Either way you need each pole/cane to be at least 2m tall, and there should be one per plant.
Plant out tender perennials once you’re sure there will be no hard frosts. Plant out pelargoniums, penstemons, arctotis, argyranthemums and verbenas, taken as cuttings late last summer or autumn. If planting in pots, integrate slow-release fertiliser into the compost to keep plants growing until next winter.

The kitchen garden

Vegetables

Plant out half-hardy annuals, or direct sow eg. French beans, carrots, sweetcorn, squash and pumpkins.
Continue successional sowing of salads, radishes, beetroots, carrots and peas, to ensure a continuous harvest throughout the summer rather than a glut of everything all at once.
In this dry weather it’s best to water the drills before sowing seeds, then cover with dry soil. Also water daily to prevent the compost drying out.
Keep banking up soil over emerging potato shoots, protecting from late frosts but also encouraging a larger yield.
In most areas of the country courgettes can be planted out now. Their large leaves make them vulnerable, so they need full sun and shelter. Soak the pots in water so they go into the ground moist.
Protect crops from carrot fly by covering with horticultural fleece or enviromesh.

Salad & herbs

Continue successional sowing of salad
Direct sow basil, particularly alongside tomato seedlings to help draw white fly away from the fruit.
Keep mint roots under control by lifting and dividing, or alternatively grow in pots. Once within a pot they can be buried within a bed with other herbs if preferred.
Perennials such as chives, lovage, fennel and marjoram benefit from a haircut now. Cut them right to the ground, and they’ll be up again in a couple of weeks.

Fruit

Strawberries are insect-pollinated so make sure pollinators have access to your plants, whether in the greenhouse or outside under cover.
Cover soft fruit plants with netting to protect from birds.
Watch out for signs of powdery mildew or disease on fruit trees and bushes, and treat with a fungicide.
Keep an eye out for less desirable insects and creatures such as vine weevil, slugs, sawfly larvae and fruitworms, particularly on gooseberry and currant bushes, and protect young fruit from birds by covering with netting or horticultural fleece

Harvesting

What you could be picking and eating this time next year, or – if you’re an old hand – already are:

Brassicas: kale, cauliflower, late purple sprouting broccoli, spring cabbage
Roots: radishes, first carrots, 1st potatoes (raised inside)
Salad crops: salad leaves, pea tips and the 1st Cos lettuce
Edible Flowers: borage and marigolds
Leafy greens: chard and spinach
Legumes: 1st broad beans (end of the month)
Squash: 1st indoor courgettes
Other veg: baby globe artichokes
Herbs: soft herbs - parsley, chervil, coriander, par-cel, 1st sorrel, evergreens: rosemary, sage, bay and winter savory, mint, tarragon, 1st dill, oregano and basil (inside)
Fruit: cloched strawberries and rhubarb and gooseberries need to be thinned on the branch

In the greenhouse

Start to closely inspect your plants for pests and diseases - early prevention is easier than curing an infestation.
Start greenhouse watering - if we have some decently hot days seed tray compost dries out in a few hours, so it may be time to start almost daily watering. Place all pots on top of water-retaining capillary matting to cut watering time by half. (This also applies to cold-frames and polytunnels).
Ventilate green house on warm days ( but close at night) & use blinds or apply shade paint to avoid large fluctuations of temperature.
Plant tagetes with your tomatoes, to act as companion flowers which deter pests. Harden off half-hardy bedding plants to acclimatise them to outdoor conditions.
With night temperatures no longer so low, tomato seedlings can be planted, but not yet outside. Use ring culture pots to maximise plant production and flavour.

Other jobs

Continue to hoe soil to keep down weeds. This should be done in warm, dry conditions to ensure any weed seedlings left on the surface dehydrate and die.
Support your tall growing perennials like Delphiniums, Peonies and Fuschia with circular plant support hoops, or bamboo canes with string.
As the weather gets warmer, pond weed can quickly get out of control if left. It’s an easy and fun job removing it, best done with a small net or old kitchen sieve. The warmer temperatures will also make any fish more active, and now’s the time to start feeding them daily.
Give your container plants a balanced liquid feed every two to four weeks to promote healthy growth.
Cut circles of capillary matting and place saucers or trays beneath your outside pots and containers to help cut watering time. I prefer this method to water-retaining granules added to the compost, as I’ve found this can cause roots to rot if there is a wet summer.
Discard spring bedding in pots - take it out once it has flowered. Refresh the soil in the pot and replant with summer bedding.
Cut comfrey back to the ground to encourage more flowers in a few weeks. Chop up what you remove, pile it into a bucket, and fill with water to make comfrey juice. In three to four weeks’ time use to feed tomatoes, beans and sweet peas – which all thrive on extra potash, abundant in comfrey.
Repot root-bound agapanthus- if your agapanthus have been in their pots for years, they may benefit from repotting. Tip the clump out of the pot, split it in half (you may even need a saw to do this) and repot both halves in the same-sized pot as the original.
Take dahlia cuttings, with dahlias growing well, now’s the time to take cuttings.
Look out for quick-growing annual weeds such as goose-grass (cleavers), climbing 1ft a week at this time of year and already flowering. You must get these out before they set seed or you’ll be playing catch-up all year.
After our full-on winter deluge, it’s a good idea to give hedges, trees and other permanent planting a boost by feeding with a slow-release organic fertiliser such as blood, fish and bonemeal.
Remove a few vigorous-looking side shoots from autumn-flowering shrubs and place straight into a plastic bag to stop evaporation. At your potting bench, remove side leaves and the tip, leaving two small leaves at the top of the stem, and reduce the cuttings to 2-3in (5-8cm). Fill a medium-sized pot with gritty compost and push in the cuttings around the outside, 2in (5cm) apart. Water and place in a cool but light spot. They should root in six weeks and be ready to plant out in 12 weeks.

Wildlife & pests

Start slug prevention - From trials at Perch Hill, we’ve found the biological Nemaslug and organic wool pellets are more effective than slug pellets. The key is to concentrate whatever treatment you’re using around the base of hedges and evergreen shrubs. It’s in the dense cover of larger plants that slugs and snails often live. If you put a good circle of deterrent around these, you’ll have the best effect.
Keep an eye out for less desirable insects and creatures such as vine weevil, slugs, sawfly larvae and fruitworms, particularly on gooseberry and currant bushes, and protect young fruit from birds by covering with netting or horticultural fleece.
Support Plant Life's No Mow May Challenge - help British wildlife by locking away your lawn mower for this month. Changing your mowing habits in this way will let more wild flowers bloom in your garden and these flowers help provide a vital source of nectar to bees and other insects.