The world-famous RHS Chelsea Flower Show takes place every May – an event that inspires the nation to sow, hoe and mow. And there’s no shortage of jobs to be getting on with this month. Here’s our guide to 10 essential jobs to do in the garden in May.
1. Keep greenhouses cool
Plants in greenhouses are at risk of scorched leaves as the sun gets stronger this month. To prevent greenhouses from overheating, shading is a must. Paint-on solutions are easily applied to roofs and sides with a paint brush – just make sure that glass is clean and dry before application. To improve air flow, open roof vents and louvres in the morning, but close before dusk to retain warmth. If you can’t be at home 24/7, install automatic roof vent openers. A maximum-minimum thermometer will help you to keep track of temperature highs and lows. During hot spells, dampen greenhouse floors with water to increase humidity.
2. Protect strawberries
Sweet, juicy home-grown strawberries are one of the joys of summer, especially if they’re ripe in time for Wimbledon. Trouble is, slugs and birds are partial to the fruit, too, while grey mould can be catastrophic. To keep rot at bay, place straw under flowers and swelling fruits, so they’re not in contact with damp soil. Take care when watering, aiming water on the soil or compost without splashing fruit. If birds are a problem, use netting raised up with canes to protect crops, but make sure birds can’t become trapped underneath.
3. Plant hanging baskets
Hanging baskets add great colour to your garden and they are easy to plant up yourself. Sit your hanging basket on a bucket and line the wire frame with moss. Fill with a compost specifically for pots and baskets, as it’ll retain moisture for longer, reducing the risk of baskets drying out. Push trailing plants through gaps in the moss from the outside, topping-up the compost as you go. Basket favourites such as busy Lizzies, trailing fuchsias and petunias should be planted into the top. Also consider bacopa, trailing begonias, calibrachoa, nasturtiums and lobelia. Firm plants in and water well.
4. Watch out for ants
Ant infestations are common as temperatures rise. Ants make a beeline for your food or drink if you’re dining al-fresco, and push soil up between gaps in paving, leaving a mess. Applying ant powder at the entrance to nests will control the problem, but if you prefer not to use chemicals, flood the area regularly with cold water. Where ants infest lawns, don’t kill nests by pouring boiling water into the entrance. It may wipe out the ants, but scalding water will kill the grass too! Repeated flooding with cold water is the best way to see off ants in lawns.
5. Toughen-up tender plants
Towards the end of May, tender flowers and veg in greenhouses or on window sills will need to be acclimatised to cooler temperatures and wind outdoors – a process known as hardening off – before being planted out in their final growing positions. This helps plants to avoid a shock that can stunt growth. The easiest way to harden off is to stand trays of plants outdoors during the day, when weather is fine, and then bring them back indoors at night, carrying on with this procedure for a fortnight.
6. Sow sweetcorn indoors
Sweetcorn is one of the most rewarding veg to grow: cobs are intensely sweet and flavoursome. Sow seed an inch deep in pots or modules of seed and cuttings compost until mid May, keeping at around 20C until seed germinates. Young plants can’t go out until June, when the danger of frost is well and truly over, so in the meantime, prepare the final growing site. Choose a sunny, sheltered spot, and dig in well-rotted manure. When planting out, position young plants in blocks 18-20 inches apart, rather than in rows, as sweetcorn is wind-pollinated. For extra-sweet cobs, sow varieties such as ‘Swift’ or ‘Lark’.
7. Trim hedges
May is a great month to tidy-up evergreen hedges in time for summer, but before you reach for the shears or hedge trimmer, remember that it is against the law to disturb nesting birds, so examine dense growth to check that no nests are present first. Hedges such as box, hornbeam and beech respond well to spring trimming. Leyland cypress hedges should also be given a haircut to prevent these vigorous growers from becoming unruly.
8. Divide primroses
Primroses and polyanthus can look unsightly now that flowering is over. Left to their own devices, clumps can flower poorly in future, so dig plants up and divide them. The process of division gives plants a new lease of life, resulting in better flowering next year. If space is needed for summer bedding, primroses can be grown on in a quiet corner of the garden after division, then replanted in their flowering positions in autumn.
9. Pot-up tomatoes
Greenhouse tomatoes may be big enough to plant into their final growing positions. If you plan to use growing bags, buy the biggest, fattest bags as they’ll allow maximum root development and retain moisture. Where tomatoes are to be grown in big pots, fill with John Innes No3 or multi-purpose compost. Cordon tomatoes, which have one central stem, will need canes for support. Tie stems to canes regularly using string or twine and pinch out side-shoots that emerge between the stem and leaf stalks. Once the first truss of fruit has set, liquid feed with tomato fertiliser.
10. Keep lawns lush
As temperatures rise and grass grows faster, weekly mowing may be required. If your mower’s blades were set high for the first cut last month, they can now gradually be lowered. However, avoid mowing too close, especially in dry conditions, as it can weaken grass and even risk scalping the lawn. Lawns that are cut too short will need additional feeding and are more susceptible to drought, while bare patches can be easily seen. New lawns, laid from turf last autumn or sown this spring, may need additional watering in warm conditions until established.
What else have you been doing in the garden this month? Let us know in the comments.
Marc Rosenberg bio
Marc Rosenberg is a freelance garden writer and editor. A former journalist with Amateur Gardening and Horticulture Week magazines, he holds seven Garden Media Guild Awards. Marc has written for publications including The Garden magazine, BBC Gardeners’ World and RHS online.