May is the month the garden really comes to life as summer fast approaches. There are plenty of garden jobs to keep us busy, with plenty of seeds to sow and jobs to do, but the warm days can be deceiving and nighttime frost is still an issue, especially in colder parts of the UK.
What to plant in May
Flower seeds to sow in May
There's no shortage of seeds to sow in the May garden, with many now being able to be sown straight into the soil outside.
Sunflowers, cornflowers, zinnias, nasturtiums, nigella, poppies and wildflower mixes can all be sown directly into beds, borders or outdoor containers.
In trays and pots you can start growing biennials and perennials, such as foxgloves, wallflowers, delphiniums, lupins and primroses in the greenhouse or on the windowsill to flower next year and years to come.
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Flowers to plant out in May
Plant out bedding plants once frost danger is over. This is the perfect time to buy petunias, violas, begonias and fuchsias.
Plant up some summer containers. Scented pelargoniums will last all summer, herbs make great pots too.
May is the best month to establish colourful southern hemisphere plants, such as hardy fuchsias, crocosmias and hardy salvias because they’ll have time to develop a good root system before winter arrives.
Vegetable seeds to sow in May
In the greenhouse start sowing your winter veg, including broccoli and cauliflower.
Sow courgettes, squash and sweetcorn indoors to be planted out next month.
Beetroot, kohl rabi, peas, parsnips and salad leaves can all be sown directly into the soil.
Runner and French beans can be planted straight in the soil towards the end of May, once all risk of frost has gone.
Keep sowing seeds in small batches roughly fortnightly so that you avoid having a glut but give yourself a longer more manageable harvest.
Vegetables to plant out in May
If you haven’t started growing yet now is the perfect time to get in young plug plants or buy young plants from garden centres and nurseries. There is so much to choose from to grow in raised beds and allotments, such as tomatoes and strawberries.
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Garden jobs for May
Have a tidy up
Clear paths of moss and weeds to avoid slipping in damp weather. A little picking here and there is good as a general rule but at this time of year, when growth is fast, it’s best to use a long handled steel brush to sweep greenery and other debris from between cracks. Or, if you own or can borrow a power washer the water jet will make even quicker work.
Read our tips for cleaning a patio and cleaning decking
Care for tender plants
In May there’s usually a frost or two still to come. If you’ve planted tender bedding, such as petunias, heliotrope, fuchsias or begonias, it’s best to cover them on clear nights. Sheets of newspaper, or horticultural fleece, will keep them snug if temperatures dip.
Feed your flowers and plants
Feeding now will pay dividends later on, but you must use a slow-release fertiliser containing potash, to encourage more flowers. Vitax Q4 is excellent and this general fertiliser can also be applied to roses, herbaceous plants and fruit. Avoid adding nitrogen-rich plant food: it produces too much leaf.
Vegetables will also respond to enriched soil. The easiest soil enhancer is well-rotted garden compost, so it’s really worth making your own if you’re able to. You can also use well-rotted manure, although spreading it in early spring can be backbreaking. However, you can also buy bagged manure from garden centres. The best way to incorporate organic matter into a vegetable bed is to put some at the base of the planting hole. Squashes and courgettes benefit hugely from sitting above organic material because it aerates and warms the soil.
For brassicas sprinkle on a nitrogen-rich feed, such as chicken pellets or powdered chicken manure, straight after planting. Root crops prefer lighter soil and are generally best grown in soil that hasn’t been enriched.
Do the Chelsea chop
Cutting the stems of flowering herbaceous perennials such as sedums and asters will keep plants smaller and encourage more flowers. This should not be done on flowers which flower only once, or flowers which are intended to be tall and striking.
Tidy up spring bulbs
Many tulips will return again and they can be left in situ. Cut them back to one leaf and remove any fading stems on garden narcissi as well. However if you’re growing wilder bulb species, like our native N. pseudonarcissus, leave the heads because species tend to spread by self-seeding.
Come summer, when the leaves have faded away, you can lift tulip bulbs, allow them to dry on wooden racks or newspaper and then store them indoors somewhere cool and dry to replant in the autumn.
Watch out for pests
Scarlet lily beetles and their brown grubs leave telltale signs of holes in the leaves of affected plants, eg lilies and fritillaries. Left alone they can soon eat their way through all the leaves.
Keep an eye on slugs, especially when its been raining. Indeed during a rain shower is the perfect time to get outside. Snails and slugs should be having a gay old time. Collect them in a bucket and dispose somewhere far away. Look behind pots and bricks and anywhere nice and dark. If you are really suffering you might want to try Nemaslug, a new nematode that predates on slugs and is safe to use around edibles and near pets.
Find out more about controlling slug and snail populations
Stay on top of weeding
Five minutes here and there (rather than a whole afternoon) with a hand or long hoe saves fingers and backs.
Thin our self-seeders
As well as weeds you will also find self-seeding plants taking off in May. Thin out gluts of self-seeders such as poppies and fennel leaving the strongest where you want them to flower, remembering that its best to keep them from flowering too close to the edges of beds.
Tidy up flower beds
Any frost-damaged leaves should be pruned back to the next healthy bud or side shoot. Frost damaged plants often recover so don’t immediately pull them up but wait until summer, giving them time to regrow. If there’s no sign by mid summer you can pull them up.
Get rid of any brown or faded material in the borders. Certain plants have already finished flowering and they can be tidied. Deadhead all, or most, aquilegias, because these self-seed far too enthusiastically. Pulmonarias and brunneras can also have their fading stems removed and the foliage can be chopped back to nothing to promote fresh, sumptuous leaves. Hardy ferns can also be tidied now. Most have either produced fresh fronds or will soon do so. Clean out any leaf litter in the shuttlecock middles at the same time.
Prune forsythia after flowering If you don’t do this every year they quickly get unmanageable and flower less well. Using sharp loppers and secateurs cut a quarter of the old growth to the base. Also remove diseased, dead, dying and wispy stems cutting them to the ground. Finally prune stems that have just flowered to two buds above the previous year’s growth.
Tie in climbers. If you haven’t tried it before Flexi-tie is a great boon, stretching as the plant grows. It is soft against stems and is frost proof. You can also keep the cut lengths and reuse them.
Start hardening off seedlings
Start hardening off seedlings of beans, tomatoes and other plants sown indoors or under glass. Allow a couple of weeks for the process gradually acclimatizing the plants. French beans can be particularly delicate so take care not to expose them suddenly to strong winds or rain or scorching midday sun.
Make a bean wigwam
Make a bean wigwam using canes or hazel stems to make a support for growing beans. Either tie the tops together to form a wigwam or else arrange the supports in long Xs that cross either half way up or close to the top. Sow a couple of beans to each cane and a few at the ends of the row as replacements for any that don’t come up. Beans are greedy plants so they’ll enjoy being grown above a trench filled with rotted manure or kitchen compost (even part rotted will do). Cover the trench with soil and then plant the beans. Once the beans are up make sure that the slugs cannot get to the growing tips because they’ll destroy the plant.
Get a windowsill herb garden going
Repotting supermarket herbs, dividing them into smaller pots, a couple of stems per small pot, will make your plants live longer, giving you plenty of fresh herbs over summer. You can use this trick on mint, coriander, basil, thyme – pretty much anything.
Tend to the vegetable patch
Thin out vegetable seedlings already planted allowing space for individual plants to flourish. Wash and use thinnings of lettuces and beet tops in salads.
Check strawberry flowers for frost damage in colder areas, net them against birds and lay down straw under the plants to protect them from rain.
If you have space in your vegetable garden it's worth growing some comfrey to make comfrey tea. Find out how to make comfrey tea here.
Read more about caring for a spring garden, including spring lawn care and the best trees for early spring blossom.
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