Things really step up in the garden through May. For much of the country, threat of frosts are gone by the middle of the month, meaning planting for summer can really begin, though the further North you are, the longer you’ll have to have frost protection at the ready – even into early June for parts of Scotland.
For those without indoor space for early sowings, this is the month to sow outside in earnest - pretty much all hardy annuals and even the half hardy types can be sown outside this month in the warming soil. Those that do make an early start will have windowsills, cold frames and greenhouses brimming with young plant waiting to go outside.
Whether you have flower and vegetable sowings to undertake, young plants to prepare for planting, or are simply looking for some green-fingered inspiration for the month ahead, we’ve got some simple pointers and ideas to get your plants and garden set for summer.
Preparing young plants for the garden
Plants raised under glass or on windowsills will be looking lush and ready to plant through May, but their soft growth is not ready for outdoor conditions. Some acclimatisation is needed for successful establishment out in the garden. Plants should be placed outside by day (unless conditions are really cold, wet and windy) and brought back under cover in the evening over a 10-14 day period, adjusting them to cooler temperatures, lower humidity and increased air movement. This toughening up process is called ‘hardening off. All young plants started from seed or plugs this spring, and any plants overwintered under glass should go through this process. Even plants classed as ‘hardy’ will need this treatment to establish them outside.
Keep new plugs under cover
Any plug plants delivered in late April, and those due to arrive this month, should remain on the windowsill or in the greenhouse until early- to mid-June, giving them time to grow to a suitable size for the garden. Plug plants destined for borders and veg patches can be grown on in small pots or cell trays. Plants for the patio can go directly into their final containers if you have the room for them in the greenhouse.
In The Flower Garden / On The Patio
- Spring perennials – get a second flush of colour from early flowering perennials such as pulmonaria and doronicum by cutting out flowered stems to encourage strong regrowth. Sadly this doesn’t work on early flowering dicentra – simply cuts plants down as their foliage fades and allow summer varieties to take their place.
- Move spring flowering violas to shadier parts of the garden for continual displays through summer. Cut back plants by half and offer a feed - they’ll bounce back within two weeks or so for a really strong summer show.
- Keep on top of seasonal growth on climbers. Tie in new stem growth with wire or twine. New shoots on self-clinging types can be tucked into their support frames to keep the summer display neat and tidy.
- Cut back trailing spring flowering alyssum and aubrieta as blooms fade, to keep the plants tidy. Use shears to cut back hard, which will encourage a new tight cushion of foliage growth.
- If fading spring bulbs are in the way of your summer planting plans, lift them once flowers fade. Drop them into pots of compost and allow them to die back naturally before storing in cool, dark conditions for replanting in autumn. If leaving in place, remove spent flowers but allow foliage to die back naturally. You can also apply a dressing of sulphate of potash to build up their energy stores for nest spring’s display.
- Mulch around mature trees, shrubs and perennials to retain soil moisture.
- Direct sow hardy annual flowers right through May
- Direct sow half hardy annuals in the second half of the month. This is particularly useful when it comes to Zinnias. These are a garden favourite but they do not like being transplanted from pots to soil. Far better results (albeit later flowering) will be had by sowing them in situ where roots can grow undisturbed.
What to prune in May
The majority of spring flowering shrubs flower on the previous year’s stem growth, cutting them back this month as flowering finishes gives them a full season to put on new shoots that will carry next spring’s flowering display. No matter the variety, all pruning cuts should be made just above a healthy bud point using clean, sharp secateurs or loppers. A pruning saw may be needed on thicker stems. Once you are happy with the overall size of the shrub, you can get among stem bases to remove older wood, improving air flow and light penetration to the centre of the plant.
Common shrubs to prune now:
- Daphne odora
Planting Project: Create a hanging veg garden on the patio
The warm, sunny locations often reserved for hanging basket displays are ideal places to grow a wide range of fruit and vegetables – simply swap your summer basket flowers for your favourite summer crops. Many fruit and vegetable plants have pretty flowers so you don’t have to give up on good looks, your edible displays can be as pretty as your floral ones. Don’t forget that many flowering plants have edibles blooms too, so you really can get creative.
What to grow - Salad leaves, herbs, tomatoes and strawberries are obvious choices for hanging baskets, but there is a surprising range of dwarf vegetable varieties across our whole range that will give great results and easy pickings in baskets.
Tomatoes are the most popular basket vegetable by far, and there is still time to sow seed or pot up some plug plants this month. Look out for bush types, listed as ‘determinate’ varieties – Tumbling Tom, Garden Pearl and Cherry Falls are some of the best for basket use.
Planting by numbers - Tomatoes should be grown one per basket, as should aubergines and cucumbers. Two or three of the smaller pepper and chilli varieties can be grown together, while five is a good number for strawberries. Salads and herbs grown for ‘cut and come again’ use can be planted thickly. You could even plant six or so standard pea or bean plants and let them trail to the floor.
Veg.Basket Planting tips:
- Always use the biggest hanging basket available to you. Small baskets dry out quickly in summer heat and restrict plant growth.
- Most veg plants will thrive in multipurpose compost, but longer lasting fruit plants like strawberries and blackberries will appreciate a 50:50 mix of multipurpose and soil-based John Innes No.3.
- It is best to plant hanging baskets by variety for ease of up keep - salads in one, runner beans in another etc., but it is always fun to get creative, so do try mixing things like salad leaves, beetroot, carrots and nasturtiums together in one display.
- Crops grown in baskets will need regular watering and feeding to maintain healthy growth. Mix slow release vegetable feed with compost at planting time. Fruiting vegetables like tomatoes, chillies and peppers will need regular liquid feeds through the season for the best yields.
On The Veg Patch
- Planting - All hardy veg plants raised under glass through spring can be hardened off and planted out this month.
- Sowing - As your first plantings of quick cropping hardy vegetables go out, make your first successional sowing alongside them. It is better to sow your favourite vegetables little and often in short rows or small patches to avoid a glut of produce. Sowing every two weeks or so through to mid July, ensures fresh crops every two weeks or so through summer and into autumn.
- Plant supports - Ensure climbing supports for peas are in place before growth really takes off this month. Supports can also be organised for runner beans and climbing beans ahead of planting in late May or early June.
- Plant Protection - Wild birds are a delight in the flower garden but can become a real nuisance on the veg plot. It’s good to have an array of plant protection equipment ready to hand at the start of the season – it always pays to be proactive rather than reactive.
Fruit cages and tunnel netting are the best options for keeping hungry pigeons off your brassicas and blackbirds off your strawberries and raspberries, but if looks or cost are an issue you might want to try these prettier, cheaper alternatives:
Scarecrows - This traditional bird scaring method can be a bit hit and miss, but they are fun to make with the family and add a touch of fun to the plot too. The trick is to add an element of movement to your design. The easiest way to do this is to leave the arms unsupported so they can flap in the wind.
- Old CDs – hanging reflective CDs in fruit trees is a common bird scaring device but it can also be used elsewhere on the veg patch. Use string or wire to hang them on or between plant supports.
- Warning colours - red is the colour of danger and will keep many bird species away from crops, but most bright colours and reflective materials should help keep birds at bay. Set lines of string over crop tops and hang with strips of red material or tin foil.
In the greenhouse/ on the windowsill
Sow frost tender summer vegetables under glass this month, ready to plant out in early/mid-June once conditions are right. With hardier plants being moved outside in coming weeks, fill the space with pots and trays of the following vegetable seeds:
- French beans
- Climbing beans
- Runner beans
Final planting for greenhouse crops - Early sown tomatoes, chillies, peppers, cucumbers, melons etc. can all be planted into their final pots, grow bags or border positions in the greenhouse. The tomatoes, cucumbers and melons in the Mr Fothergill’s polytunnel are planted into 10 litre pots and grown this way to harvest. Chillies and peppers are set into 3 litre pots then set on top of grow bags to root into the compost below. These methods consistently encourage excellent yields and plant vigour.
Sowing flowers - You can continue to sow hardy and half hardy annual flowers inside, but to save on maintenance, you may prefer to start sowing outside. This will free up space for early sowing of biennial and perennials for planting out in autumn or next spring.
6 essentials tasks for the greenhouse
Ventilation - Open greenhouse doors and windows each morning. Day temperatures can still fluctuate in May – think about adding automatic openers to roof and louvre windows so they close when temperatures drop too low. Close windows and doors each evening.
Raise Humidity - With good ventilation it is safe to raise humidity around greenhouse plants, helping to keep them cool during the hottest part of the day. Wet all hard surfaces in each morning. The water will evaporate and raise the humidity level around your plants.
Shading - Young plants growing under glass can quickly frazzle under direct summer sunshine. This can be prevented with shade paint or shade netting added to the south side of the greenhouse. Newspaper can also be used as a temporary fix.
Heating - There should be no need for daytime heating in May, but in case of overnight frosts it is worth keeping an electric heater on its frost guard setting, or setting a paraffin heater in place each evening though to June.
Water Wise - Prevent potted plants drying out during the day by setting them in trays lined with capillary matting. If pot compost dries, water is drawn up from the soggy matting via the pot drainage holes.
Pest Watch - Set sticky yellow traps just above the foliage of greenhouse plants to keep an eye on potential pest problems. As soon as troublesome pests like aphids or whitefly are spotted, action can be taken before a major problem occurs. Have appropriate spray controls ready hand or be ready to order biological controls.