What to do and look out for in the garden in May

02. May 2021 by Isabelle Van Groeningen
Categories: About gardening, english, Seasons, Spring | Leave a comment

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Staubenbeet mit Tulpen © Isabelle Van Groeningen

Flagge Deutschland für deutsche Übersetzung – auf Deutsch lesen – These weeks are my absolute favourite time of year. During this cold, slow spring. each plant group has its moment of glory, making way for the next as it fades. I always think of it as the cloud weeks: One big, airy flower cloud follows the next, ranging from white to all shades of pink. The flowering clouds of cherries and plums are now being followed by clouds of magnolias and the blossom of apples and crab apples.

The early rhododendrons and Japanese azaleas are starting to show colour, and kick-start the colourful season that lies ahead.

Nearer to ground level, the larger bulbs are starting to play their part. In the big borders at the Garden Academy the early tulips are gaining in colour from day to day. In my shady garden at home, the delicate shade-loving perennials have started flowering and provide a rich tapestry of flowers. Epimediums, Lathyrus vernus, Bergenias and Lungwort all look delicious. Annual and perennial Forget-me-Not create fluffy bright blue clouds. In between all the richly textured foliage, treasures pop up such as Erythroniums, Trilliums and other delicate woodland plants. The little starry pale pink flowers of Montia sibirica are starting to appear there where the seedlings found sufficient space and light to establish for their short life. In sharp contrast to the light and airy character of these flowers, the brutal masculinity of Podophyllums and Arisaemas pushes through. These are complimented by fern fronds unfurl themselves, and have distinctive primitive, animal-like feel to them.

Zwiebelsichtung © Isabelle Van Groeningen

Frost-damaged woody plants

The night frosts of the past weeks have caused damage to some eager shrubs and climbers. It is really upsetting to watch tender new leaves turn brown and crispy. If you are lucky, just the first leaves were caught, and the shrub will soon produce new ones. If the plant was already further advanced, then cut them back into healthy, undamaged wood. They will re-grow, but will need some time to catch up. More dramatic is when flowers were caught by frost. I have spotted quite a few magnolias that suffered badly, as well as fruit trees. Sadly there is little you can do about this, other than hope that the plant soon outgrows the brown mess. I am always amazed at the resilience of plants. The crown imperials would hang limp every morning, their green foliage crown that tops the flowers a sad, floppy mess. As morning progressed, you could watch them lift themselves, by noon all was fine again. A similar effect I have observed on peonies.

Planting time

The long cool spring is ideal for planting. Even if a light night frost is forecast, you can go ahead planting trees, shrubs, roses and perennials. Make sure you water the plants well before and after planting.

Weed control

Annual weeds are making the most of this slow start of the season. Normally our border has already quite a dense vegetation cover by now, but this year the plants are much slower coming into leaf. As a result, weeds such as chickweed, speedwell and bittercress are happily making the most of the opportunity. As I fear the persistent cool weather is not going to change much to the situation, we have decided to tackle the problem and weed them out before they get the chance to flower and set seed.

We replanted a border that was infested with ground elder. A few cheeky roots that escaped our digging and are sending up new shoots now. Now is the perfect moment to dig these young plants out with a small hand fork, before they get established again.

The Dandelion season is upon us. A meadow glowing yellow with dandelion flowers is a lovely sight, as long as it is not in your garden or just next to it. Mow the grass, collecting the clippings, and avoid putting these on the compost heap: dandelion seeds will continue to develop and ripen, long after they have been cut.


Schnitt von Frühblüher Lonicera x purpusii © Isabelle Van Groeningen
Schnitt von Frühblüher Lonicera x purpusii

spring flowering shrubs such as Forsythia can be pruned as soon as the flowers are finished. Now is also a good time to look at your bamboos and check if they should not be thinned out a little and tidied up.

Things to do in the flower garden

Bulbs: However tempting it may be to remove the foliage of tulips, daffodils and other spring bulbs as it loses its fresh appeal, do not touch it!  It is important to allow the plant to absorb as much energy through photosynthesis as possible. Leaves and stems should stay, all you can remove after flowering is the actual seed capsule. These usually snap off quite easily. If you have not yet fed your bulbs with a bulb fertilizer, now is the time to do so. We never dig out our bulbs after flowering. The small, early bulbs such as winter aconites, crocus, anemones and scillas are best left alone. The chances are that they will set seed and self-seed, thus slowly increasing the flowering display from ear to year. Most of these will require about four years to develop new bulbs large enough to flower.

Primeln teilen © Isabelle Van Groeningen
Share primroses

Dividing early spring flowers: Early perennials, many of which are shade lovers such as Lungwort, can be lifted and divided after flowering. This way you can increase their flowering impact in years to come. Likewise, now is still time to lift and divide larger clumps of snowdrops.

Staking straggly perennials: Some perennials have a tendency of falling apart or toppling forward as they seek more room and light. IT is easier to give these some support before it happens. May is a good time to put a few twiggy sticks in between messy Geraniums such as ‘Rozanne’, provide some hoops or metal grids for your heavy-headed double peonies, and sturdy sticks for the large flowered Dahlias.

Tidying evergreen perennials:

Hellebores: I did not cut back the old foliage of my hellebores before they started to flower, as they still looked good. Now they are starting to look shabby, so now is a good moment to cut them back. Making space for new leaves. As long as the seed heads have not started to dry they look attractive and they are allowed to stay.

Ferns: The old fronds of evergreen ferns start to look shabby as the new foliage emerges. if this really bothers you, you can cut these off.

Euphorbia: My favourite Euphorbia characias is only moderately hardy. Those of you fortunate enough to grow them, should cut back the flowering stems when they start to go brown, leaving the new shoots that will flower next spring. Thanks to the cool weather, this job can probably wait till June. Just be careful to avoid direct contact with the milky white sap on sunny days, as this can cause burns.

Things to do in the vegetable garden

Basilicum © Isabelle Van Groeningen

In recent weeks I  have sown the first batches of salads, chard, spinach, parsley, chervil, dill, radishes, beetroot, carrots, spring onions, broadbeans and peas.

Looking after seedlings: As they germinate I like to keep an eye on them to make sure there is no invasion of slugs, that they stay sufficiently moist, do not get overwhelmed by weeds and are thinned out to the recommended spacing so that they can develop into strong, healthy adult plants.

Succession-sowing: Most vegetables I only sow in short rows, but like to repeat-sow every three to four weeks, ensuring a constant supply of fresh vegetables, without ending up with an enormous glut or periods with little to harvest.

Tender vegetables: In a few weeks’ time I will also sow beans and in late May will plant out the young plants of basil, tomato, pepper, zucchini, squash  and cucumber. Everything that is frost-sensitive has to wait till May before I can trust them to be ok outside.


The lawn should be fertilised by now with a slow-release  spring lawn feed. If you have planted bulbs in the grass, leave them for 6 weeks after flowering before mowing. Otherwise, start a regular mowing programme now.

There is much more to do, but above all you should take the time to enjoy your garden!

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