Monthly Advice - May Jobs in the Garden



  • Formal evergreen hedging such as Yew responds well to a light trim in May, even if it has not reached its final desired height (in which case trim the sides, but NOT the tops). You are then encouraging the plant to grow more bushy, but (hopefully) not endangering any shorn shoots by exposing them to frost. 
  • They used to say you should clip your box hedges on Derby Day but with the rise of box blight, it is better to do this in winter when fungal spores are dormant and will not attack fresh wounds on leaves and stems.  
  • Remember to keep newly planted hedges well watered in May and June.  
  • Don't panic if your beech hedge is still not in leaf. It happens late, especially with newly planted beech (and copper beech).
  • Lavender is the best small summer hedge and edging plant. Order now for delivery this month. 

Fruit Trees

  • At last, you can unwrap your peach, nectarine and cherry trees from all their polythene protection. The risk of peach leaf curl is over but while your trees are still in blossom continue to check the weather forecast for night frosts and keep a large swathe of horticultural fleece to hand to drape over your tree should you think that the temperature is going to plummet. Frozen buds mean no fruit in the autumn and frosts can happen in the first half of May.
  • Fruit trees with pips (apples, pears, quinces etc) should have been pruned in winter but the stone fruits like cherries, plums and nectarines are far better pruned in late spring/early summer. They can suffer from silver leaf disease but this cannot enter fresh pruning cuts because the rising sap prevents ingress and seals the wound. The idea is to assess any young side shoots grown this year and when there are six leaves, pinch out the growing tip. That way you should not end up with lots of little fruit but with fewer fruit of a decent size.
  • Morello cherries, so beloved by cooks, work slightly differently because they fruit on two year old wood and need training in a different way. One ongoing method to manage this is to tie in a 1 year old shoot to produce this year’s fruit and next to it, tie in a new shoot grown this year. Do not prune these two shoots but remove any others. In autumn, once the fruit has been picked from the 1 year old shoot you can cut out the fruited shoot completely and its neighbour will be ready to fruit next year. You will then need to remember to tie in a new shoot next year.
  • As with hedging, you can still plant bareroot stock this month if it was held in cold store. Ours is... :-)

Garden trees

  • Water, water. The only thing to say here is to keep up your watering regime; any new woody plant with young, establishing roots and bulging leaves and buds is going to needs lots of water to combat drying winds and warm(er) days. You need to keep this up until its roots have grown down to find water deeper in the soil. If you have sandy soil, you may need to water every day. A mulch in the form of a mat or a circle of spent mushroom compost or rotted manure will prevent evaporation from the ground around the roots and seal the moisture in. But make sure the soil is really well watered first as mulch will also keep it dry... A timesaver for the person on lawn-mowing duty is to tip about 5-8 cm of grass cuttings around the base of trees as another layer of protection and to save you having to tip the cuttings in the far corner of the garden, or even bag them up and take them to the recycling dump. Ideally The clippings should not touch the actual stem of the tree. Trials have shown that trees which are mulched properly so weeds are suppressed and water is retained will grow 70% better than those left to their own devices.


  • Continue the aphid patrol but also look out for any signs of black spot. This fungal disease not only makes the leaves look awful, but it can easily kill a rose and will certainly affect its vigour. It is a good idea to spray against black spot when the leaves first open; prevention is better than cure.  However, if you see any tell-tale signs of black spots on yellowing leaves, remove the shoot as quickly as you can and burn it. Collect any leaves that have fallen and burn those too. Never put them in the compost. Use a spray like Bayer’s Systhane Fungus Fighter which was recommended as the most effective Black Spot preventative around - - but be warned that you need to keep spraying over the season. In addition, water plants at the root so that you do not splash any fungal spores from buds or leaves onto other buds or leaves further down the plant.
  • Continue to tie in shoots sent out by rambling or climbing roses. Maximise the number of flowers produced by keeping the shoots horizontal. 

Soft Fruit

  • The first white, hard strawberries should be in evidence. Protect them from mud and slugs as they ripen by tucking in straw underneath and around the plant or invest in some strawberry matting. As the strawberries redden, attack from the air is also a concern: put netting over your plants and make sure that it is taut and secure so birds do not become entangled in it. Alternatively use horticultural fleece to cover them. And while you are in the strawberry patch, cut away any runners growing from your strawberry plants. These sap a great deal of energy at the expense of the crop. Removing the runners also makes it easier to surround the plant with straw. If you want to propagate some new plants, the best way to do so is to sacrifice this year’s fruit on a few plants by picking off any flowers or unripe strawberries and letting these plants produce masses of runners and new little plants that can then form the basis of next year’s crop. To find out more about strawberry crop rotation have a look at /gardening-advice/growing-soft-fruit/facts-about-strawberry-plants .
  • While we are on strawberries, anyone who was organised enough (aka determined enough to have their strawberries ready for Wimbledon) to use cloches should remove them for at least part of the day so that pollinating insects can come and do their stuff otherwise you will not get any fruit. If in doubt, you could use a small soft paint brush (or for the old fashioned, a rabbit tail!) to transfer pollen from one flower to another to ensure fertilisation.
  • It is worth revisiting your raspberry cage to check the number of new canes that are coming up. If too many grow then your raspberry plant is expending all of its energy on cane production and you will see fewer raspberries so remove a few canes where they look crowded. Doing this you will end up with sturdier canes, and being spaced apart, the sun can ripen your fruit more easily. Also if lots of canes grow close together they reduce the airflow between the plants, damp air builds up and your raspberries will be more susceptible to botyritis or other fungal diseases that make the fruit go brown and rot.
  • If May is dry, then water fruit plants really well – better to soak your plant really properly once a week. If you water shallowly it encourages the roots to come to the surface making the plant less stable while the roots are more likely to dry out and be damaged if weeding around them. Once watered either replace the existing mulch or add a mulch of spent mushroom compost, ash for raspberries, or the ever necessary well- rotted compost or manure. 


  • Clematis Montana is spectacular in May. Once the flowers are over, towards the end of the month, you can prune montanas hard if they are growing too large. As vigorous climbers they will envelop large trees, sheds and walls in spectacular fashion and do not need annual pruning but if you are trying to confine them to a smaller area or you are finding that the flowers are all at the top and not at the base of the plant, then untangle the shoots where possible and remove any dead or diseased wood. Then cut any stems back to where you want. Next year it will flower even more abundantly.
  • Pyrocantha that is trained up a wall can be pruned back now – especially if it is climbing into gutters or drains. Take out shoots growing directly into the wall and reduce the breastwood (shoots growing away from the main branches to about 8cm long. The resultant short spurs will flower and fruit more beautifully next year.
  • Keep checking on all climbers like honeysuckle, wisteria, clematis, and jasmines because they have massive growth spurts at this time of year and if you do not keep tying in new shoots you will find that they tangle badly and/or become irretrievably involved with neighbouring plants, potentially smothering them in the process. Keeping the shoots well spaced will make for better flowers because you will expose each shoot to the sunlight. 


  • May is one of the prime lavender planting months. If you have not ordered already, then do so soon. Remember that good sized plants make for near instant low, colourful, scented hedges. 
  • Water newly planted lavender until it is established.
  • Existing hedges will be growing away well by now - you can still trim REALLY straggly plants early this month to help them regain shape later in the summer. Last chance to do this though as you will sacrifice some flowers if you do this later than the first week of May.


  • The great dead-head should continue: snap off the heads of spent tulips or lingering daffs leaving the stalks and leaves intact to die down over a minimum of 6 weeks so that the nutrients can be reabsorbed into the bulb to provide fuel for next year. If you are changing around a spring display that included bulbs with flowers like forget-me-nots or wallflowers, dig up the tulip or daffodil bulbs carefully leaving the roots intact and place them in a shallow trench. Cover the bulbs with soil, LABEL (one never does actually remember!), and wait for the foliage to die down before lifting the bulbs completely and storing them somewhere frost free and dry. You can then re-use them next year.
  • Sprinkle a general garden fertiliser around bulbs in situ to give them the best chance of flowering well again next year. Water the fertiliser in if there is no immediate rain forecast.
  • Alliums will be in full swing in May. Some of the larger ones like Christophii might need some gentle staking unless grown next to another supportive perennial. Either way, the heads look fantastic even once the colour has faded making it one of the few horticultural examples of not cutting back spent flowers. 
  • Start making notes about bare patches in your garden that could use a bulb or two next spring. These will need ordering in July/August for planting in September for best results.

Olive and Bay

  • It is easy to forget the fact that the combination of roots in a pot made warmer by being above ground and the constrained space means that trees in containers require watering regularly. Your olive tree will need its monthly phostrogen fix too.

Other Stuff - including soils, lawns, ponds, terraces

  • May favourites include those wonderful alliums and drumstick Euphorbias – watch the sap on the latter if you decide to use them in flower arrangements.
  • Fill your house with the amazing smell of lilac; strip the leaves from the stem because they are so enormous and require so much water that without doing this your flower will wilt. Sear the base of each stem in boiling water for ten seconds and leave to soak in cold water overnight before arranging them in vases. Overkill it may sound, but it will mean you have upright flowers and scented rooms for ages.
  • Go and see a bluebell wood – there is almost nothing more spectacular. And while you are at it, buy a National Gardens Scheme Yellow Book and visit some other gardens in your area.
  • Succession sowing is the mantra in the vegetable garden for leafy salad crops like lettuce, chard and spinach, or herbs like chervil or coriander and also for beetroot, broad beans and radishes. If you can discipline yourself to sow a short row often you will end up with a manageable supply of produce rather than the glut that often precedes despair at what to do with all those beans/lettuces etc.
  • Sow some French and runner beans in pots in your greenhouse, but sow some outside too so that they come on later. Sweetcorn, courgettes, marrow and squashes are also best sown in this way in May too. Because sweetcorn is wind pollinated, plant it in blocks not rows so you will get better cobs. All of these plants attract slugs and snails so once you have planted the seeds or the seedlings out, use a halved plastic water/fizzy drink bottle as a protective cloche.
  • Earthing up potatoes is a necessary evil for two reasons. As you keep covering up more of the stem it encourages the plant to send out more roots which equals more potatoes. At the same time you will also bury any shallow potatoes preventing them from going green and becoming poisonous. The accompanying mint required for all boiled potatoes is easy to grow but invasive, so confine it to barracks in a pot or lift and divide any mint now and remove any wandering roots.
  • Broad bean tips should be pinched out to prevent blackfly infestation once the plant has begun to flower all over. Add the tips to risotto or braise them in butter.
  • General garden maintenance is going to see your hoe in action keeping weed seedlings down in the borders and the vegetable garden. Try to hoe on a dry day because you can leave the weeds on the soil where they will shrivel and rot back down which saves you having to rake and pick them up. Hoeing annual weeds and digging out perennial ones should be a regular chore to stop small weeds becoming large and invasive. It also breaks the cycle by preventing the weeds setting seed.
  • May is a bountiful month for lawn weeds which need tackling, while the grass will need fertilising. Lawn purists will probably try to do the two jobs separately, but there are lots of good ‘feed and weed’ products on the market that will save you plenty of time. However tempting, do not overdose your lawn with any product. You can always have another go if the weeds do not all disappear the first time.
  • Lawns need mowing at least weekly during the growing season. While you should be aiming for a closer cut each time, if you cut the grass too short you will end up with yellowed grass and then bare patches where weeds and moss can easily get in and proliferate. Remember that longer grass needs less water...
  • May is also perfect for sowing new lawns before the weather becomes too hot for the grass to germinate. Once the initial germination has taken place let the new grass grow to 2 cm high and then roll the area again. Not only does this ‘crack’ any seed that did not germinate first time around but it encourages the grass to shoot from the base of the plant so that you get a good thick sward.
  • Make nettle soup from the top four or five leaves of a bunch of nettles that grow away from polluting roads. Use rubber gloves to pick them (obviously!) and wash well before using. Or experiment with nettle pesto or nettle risotto – they are all delicious and nettles are packed full of iron and vitamins. 
  • Clean off the barbecue.

Have a nice cup of tea, in the sun, on the terrace....

Tags: advice  May 
Hi, just a note to let you know that we do use cookies to help us determine what our customers really want and therefore to give them the great service that they deserve. We also use cookies to enable you to buy products from us online in a convenient and secure manner.

Thank you, The Ashridge Nurseries Team.

Back to top