May is a time of activity and growth in the garden. This month’s full moon is the Flower Moon or Corn Planting Moon, so-called because many crops and flowering plants can now be sown outside.
In late May, some half-hardy annuals like cosmos and zinnia can be direct sown and, after all risk of frost has passed, tender seedlings can be acclimatised and planted out in the garden. There’s also still time to sow more tender annuals, such as sweetcorn, cucumbers and melons, under cover until the end of the month.
More seed sowing advice:
May is a great time to sow annual poppies like field poppies (Papaver rhoeas), opium poppies (Papaver somniferum) and Californian poppies (Eschscholzia californica). Poppies dislike root disturbance, so sowing in situ is best. Scatter seeds onto prepared soil, raked to a fine tilth, choosing a sunny site with well-drained soil, and thin seedlings if necessary. Most plants should bloom this summer. If you leave a few flowers to self-seed, you should get poppies in years to come, or you can collect seedheads to sow next spring. Deadheading faded blooms controls the spread if plants are outgrowing their allotted space.
The wild field poppy is often included in cornfield seed mixes along with other annuals such as corn cockle, cornflower and corn chamomile. There are also field poppy varieties with double flowers and more subtle shades, such as ‘Angel Choir Mixed’, which is a selection of gorgeous double-flowered poppies in apricots, palest pinks and soft grey-purples.
There are many beautiful varieties of opium poppy in a range of colours from white and greys to luscious pinks and burgundy. P somniferum ‘Maanzaad White’ has single flowers with pure white petals and soft purple markings. At the other end of the colour spectrum, P. ‘Black Swan’ has finely-cut burgundy-red petals that dazzle the eye.
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California poppies are wonderful plants for attracting bees and other insects to the garden as (like all poppies) they produce lots of pollen, despite having no nectar. We love the way the delicate flowers of Eschscholzia californica ‘Orange King’ create splashes of vivid colour in the borders. Along with this fiery beauty, we’re sowing E. californica ‘Apricot Chiffon’ from the Thai Silk Series this year, which has glorious apricot-peach flowers with a warm yellow centre.
If you haven’t sown French marigold (Tagetes patula) yet, there is still time to sow these reliable, half-hardy annuals outdoors. Sow seeds directly into well-prepared soil and cover lightly. Thin to 15cm and keep well-watered. French marigolds prefer a sunny spot in well-drained, fertile soil.
Many varieties come in cheerful shades of yellow, orange or red, and some have eye-catching patterns, like ‘Jolly Jester’ which has petals with deep red and yellow stripes, and ‘Naughty Marietta’ with her yellow flowers with burgundy blotches. For varieties with a profusion of petals, try the warm pinky-red blooms of ‘Strawberry Blond’ or ‘Carmen’ with her deep red flowers with yellow centres.
Aquilegia are in flower this month, creating a naturalistic effect in cottage garden borders or dotted through gravel gardens, as well as providing nectar for a host of pollinating insects. Thriving in full sun or partial shade, these delightful short-lived perennials readily hybridise if they like the conditions, so self-sown plants are unlikely to look much like their parents.
As well as enjoying new hybrids popping up in the borders, there are many fantastic aquilegias to grow from seed like wild A. vulgaris or showy A. chrysantha ‘Yellow Queen’, with its elongated lemony spurs. The delicate mocha and cream flowers of A. viridiflora ‘Chocolate Soldier’ have an understated beauty, or you could try a lucky dip with ‘Barlow Mixed’ or ‘McKana Giant Mixed’. We sowed A. ‘Munstead White’ several years ago and planted them out under our apple espaliers where they bloom alongside the apple blossom and Tulipa ‘Spring Green’.
Sow seeds under cover in a seed tray and keep at 15-20°C. Germination takes between one and three months. If germination isn’t successful or to speed up the process, place the seed tray in a polythene bag in the fridge below 5°C for three weeks, then return to warmth. Take the tray out earlier, if seeds begin to germinate. Grow seedlings on until large enough to handle and transplant into 8cm pots. Harden off and plant out after the last frost. Aquilegia seeds can also be sown directly in borders from this month until the end of June and thinned to 30cm apart. It is worth noting that seeds are harmful if eaten.
The unusual, papery blooms of strawflowers (Xerochrysum bracteatum or Helichrysum bracteatum) work beautifully in arrangements and, once dried, last indefinitely, hence their other common name of ‘everlasting flower’. These half-hardy annuals are easy to grow from seed. They can be sown outside this month in well-drained soil in a sunny position. Alternatively, strawflowers raised from seed in early spring can be planted out once all risk of frost has passed. Sow seeds thinly in soil raked to a fine tilth. Keep moist during germination, which takes between one and two weeks. Thin seedlings to 30cm, when they are large enough to handle.
We love the exquisite shades of ‘Salmon Rose’, which range from ivory to pale peach and coral-pink. ‘Purple Red’ demands attention with its dramatic ruby-coloured flowers, and ‘Golden Yellow’ creates a dazzling impact in borders and vases. Or you could sow ‘Swiss Giant Mix’ to enjoy a brilliant array of brightly-coloured blooms right through from July to October.
After the frenzy of spring sowing, we always end up with surplus seedlings that we are loath to consign to the compost. You can make the most of these excess plants by swapping with other gardeners who have grown different crops or varieties.
Take your seedlings to community garden days, gardening groups, set up a seedling table at work or swap them over local social media groups. Spring fêtes and open garden days are often great places to buy reasonably priced plants. And don’t forget to check out the clearance areas in garden centres and nurseries for leftover seedlings that could be revived with just a little TLC.
Greenhouse cucumbers, such as all-female varieties ‘Bella’ and ‘Mini Munch’, can be sown in pots now, 1-2cm deep, and kept at around 21°C. Outdoor ridge varieties like ‘Marketmore’ can be sown outside in a sheltered, sunny spot from the end of the month and into June. I particularly like the all-female ‘La Diva’ which produces crisp, seedless cucumbers, either in the greenhouse or outdoors, and sweet-tasting ‘Crystal Lemon’ with its unusual round yellow fruits.
Most greenhouse cucumbers are all-female. If the female flowers of greenhouse varieties are pollinated they will produce bitter fruits, so remove any male flowers that do appear. Outdoor varieties have both male and female flowers, and need to be insect pollinated, so leave male flowers on the plant. Don’t grow outdoor cucumbers under cover alongside greenhouse varieties to avoid cross-pollination which will result in bitter fruits.
One of the cucumber’s diminutive relatives, the cucamelon, can also be sown in pots this month and will start cropping from mid- to late summer. This vigorous climber produces tiny fruits with a fresh limey-cucumber flavour. They are fairly easy to grow, but it is important to harvest cucamelons when they are still dark green and no bigger than a small grape. Any larger than this and they quickly become pale and rubbery.
One of the tastiest pleasures of summer is harvesting the first beetroot and adding its earthy flavour to salads and savoury tarts. Seeds can be sown direct this month 2.5cm deep and 10cm apart, leaving 30cm between rows. Beetroot works well sown successionally to provide tender beets throughout summer and into autumn. Crops sown this month should be ready to harvest in July and August.
‘Detroit’ is a superb, high-yielding variety with tasty red beets and ‘Cylindra’ has all the vibrancy of other crimson beetroot, but with unusually-shaped cylindrical roots. Both varieties store well. We love to grow the vivid beets of ‘Rainbow Mixed’: our favourite in the collection is ‘Chioggia’, with its concentric pink and white rings showing clearly when you cut it in half. ‘Burpees Golden’ is a sweet variety with bright yellow flesh and ‘Albino White’ is a tasty beet whose pale flesh avoids the staining problems of red beetroot varieties.
Turnips sown this month will provide a crop of turnip greens that can be cooked like spinach, followed by a summer harvest of sweet roots. These easy-to-grow brassicas prefer cool conditions and thrive in moisture-retentive, fertile soil, enriched with organic matter. Sow seeds thinly at a depth of 1cm, and leave 30cm between rows. Thin seedlings to 10-20cm apart. Turnips vary in colour and shape from the round, white roots of ‘Snowball’ to ‘Purple Top Milan’ which has flat-topped roots flushed purple on the crown. ‘Atlantic’ is an ideal variety to grow in containers where it can be harvested within a few weeks for tender baby turnips.
What else to sow in May
- Flowers: achillea, anchusa, foxglove, quaking grass, larkspur, sunflowers, nasturtiums, cornflowers, nigella, zinnia, cosmos, nicotiana, brachyscome, annual salvia, annual rudbeckia, calendula
- Vegetables: French beans, runner beans, peas, carrots, parsnips, Brussels sprouts, winter cabbage, cauliflower, kale, kohlrabi, sprouting broccoli, Swiss chard, chicory, lettuce, spring onion, radish, spinach, sweetcorn, courgette
- Herbs: rocket, parsley, dill, basil, coriander
One of the best ways to avoid buying unnecessary plastic is to reuse existing pots, trays and other plastic equipment for as long as possible. Once plastic pots and trays are no longer reusable, recycle them if you can and consider plastic-free, biodegradable alternatives. Choose natural twine rather than plastic string, fibre pots instead of plastic plant pots and make soil blocks for seeds or use toilet roll inners rather than sowing in plastic modules.