After months of rain, April has been sunny and warm with few April showers. Lack of rain means the soil has dried out and plants have become stressed to the extent that irrigation has been necessary. However bees, butterflies, moths and damselflies have all been enjoying the weather and emerging from hibernation, pupae or larva to bask in the spring sunshine.
With blossoming hawthorn, May has arrived. The days are longer and warmer, growth everywhere is rapid, and wildlife fills gardens with frantic activity. Our native bluebells carpet the woods, creating a haze of violet blue, the hedgerows are laced with cow parsley and meadows are dotted with buttercups. Butterflies are emerging from hibernation, hoverflies and bumblebees flit from flower to flower seeking nectar. There is so much to see, to enjoy and to do, seed sowing, planting, cutting back, weeding and simply appreciating our green spaces and countryside.
In the garden
Gardens are blooming this month with the flowers of many plants on show or emerging. These include the floriferous (Clematis Montana), the flowers borne on their rampant and vigorous climbing stems; the elegant, pendulous flowers of wisteria; the trumpets of columbine (Aquilegia sp.), reminiscent of old fashioned bonnets, the intoxicating scent of lilac flowers (Syringa sp.) and Mexican orange blossom (Choisya ternata) and the distinctive purple globes of the ornamental allium (Allium Hollandicum ‘Purple Sensation’). Brilliantly coloured geum cultivars are beginning to flower with euphorbias bringing a contrasting lime green to spring borders.
Gardeners with acid soils may be treated to a showy display from vividly coloured Azaleas and Rhododendrons. These create a wonderful spectacle in woodland gardens such as the Isabella Plantation in Richmond Park at this time of year. Many other woodlanders also flower in May, trying to reproduce before the tree canopy becomes too dense and restricts the light. Foam flower (Tiarella cordifolia), bleeding heart (Lamprocapnos spectabilis), corydalis (Corydalis flexuosa) and Siberian bugloss (Brunnera macrophylla) are all putting on a good show.
With all of this growth, colour and nectar, garden wildlife is flourishing and working hard; pollinators are fluttering and buzzing away collecting nectar and pollinating plants; caterpillars are beginning to emerge and looking for a snack; the dawn chorus is rousing and throughout the day birds are foraging for food for their fledgling chicks. Pause a moment and appreciate the cycle of life that is taking place.
Container grown fruit and vegetables
Herbs, vegetables and fruit can easily be grown in pots, inside by a sunny window or outside on a windowsill, balcony or backyard. The most important thing to remember with pot grown plants is that they can dry out very quickly in warm weather, in the heat of the summer, with no rain, they may need watering twice a day. Not surprisingly ‘Grow your own’ has become very popular during the lockdown so online supplies of seeds and plug plants can be difficult to source or have a long lead in time. Although garden centres have been closed, many now have a delivery or collect service so you can try these too for supplies.
Herbs are very easy to grow from seed in a pot or window box. Chives, dill, oregano, parsley, mint, thyme, coriander and basil can all be sown now. Just dampen the soil, sprinkle the seeds on the surface of your container, cover with a fine layer of soil and water in. Covering the container with a clear plastic bag or cling film will keep the moisture in until the seeds germinate. Once the seedlings are visible, remove the cover and water daily or as necessary depending on rain and sun. If the plants grow too closely together thin them out and use the thinnings in salads. The containers can be kept inside or out.
Baby salad leaves, a pick and come again crop, can be harvested young. Picking small allows them to be grown more closely together. At this time of year you can sow cos lettuce cultivars, batvian lettuce types, spinach, pea shoots, sorrel, chives and wild rocket in a pot of mixed green leaves for harvest in a month or two. You can get 2-3 harvests from the leaves if picked from the outside before needing to re sow.
The flavour of home grown tomatoes, placed in a sunny spot, is unbeatable. At this time of year it’s too late to sow seeds so buy small plants online or from a garden centre. Tomatoes need sun and shelter, with a high nitrogen liquid feed such as concentrated seaweed, given weekly. Dwarf and trailing varieties are good for window boxes, hanging baskets and pots. Try ‘Little Sun’, ‘Maskotka’, ‘Cherry Cascade’, red or yellow ‘Tumbling Tom’, or red or yellow ‘Sweet and Neat’.
Chillies plants can be very abundant, they are grown in a similar way to tomatoes so best to buy plugs or small plants now. They too need sun, shelter and feeding to thrive. ‘Numex Twighlight’, ‘Prairie Fox’ ‘Appache’ and ‘Habanero’ are all good. If you have too many to be eaten fresh they freeze well for use throughout winter.
If you have space for a large pot, small dustbin (with drainage holes) or a potato grow bag, potatoes are very easy and rewarding to grow. Half fill a container with multi purpose compost and plant the tubers as soon as possible. As the stem and leaves grow, earth up with more compost around the stem. The potato tubers will grow up in layers around the stem. Preventing the tubers from being exposed to the light like this stops them going green. ‘Orla’, ‘Anya’, ‘Duke or York’ and ‘Charlotte’ are all varieties worth trying. Let the foliage yellow and wither before harvesting and protect the plants with horticultural fleece if blight, an air born virus, is forecast. (Warm, damp weather.)
Other vegetables are good in pots too: A single courgette plant in a large pot, ‘Buckingham’, ‘Midnight’ or ‘Patio Star’, can produce several fruits a day and the flowers can be used raw in salads or dipped in batter and fried. Radishes such as ‘French Breakfast’ are quick to mature and best harvested young, before they get woody. Dwarf French beans are small, tender plants that can be clumped in a pot. Sow them around 10cm apart and keep inside or under plastic until the last frosts have passed. In London this is in early May. ‘Purple Queen’, ‘Amethyst’ and ‘Golden Teepee’ are all tasty.
Strawberries are compact, productive plants and can be grown in pots and hanging baskets. A simple tiered pot of descending sized plastic pots increases the number of plants that can be grown in a small space. Plant 3-4 plants per 30cm squared in a good quality, multi purpose compost with added general fertilizer, snip out the runners as they grow, they take energy needed for the plant to fruit, shade the containers to prevent the roots becoming too hot, water frequently but not too much. When the plants come into flower, add a liquid potash fertilizer, low in nitrates to promote fruiting. Putting a layer of straw between the plant and the soil for the ripening berries to rest on, keeps them from rotting if it is wet. Good summer varieties are Cambridge Vigour, Florence and Hoeyoye. Good perpetual varieties, those with a longer fruiting season, are Elvira, Aromel and Flamenco.
Blueberries are best grown in pots. They need an ericaceous (acid) soil so normal garden soil is not usually suitable. The plants produce not only delicious, nutritious berries but have beautiful autumn colour. Plant in acid compost, place in a sunny spot for best results, water with rain water as tap water is alkaline and feed monthly with an ericaceous fertilizer. Blueberries crop better if a second, different cultivar is planted nearby. Try ‘Patriot’, ‘Bluegold’, ‘Sunshine Blue’ and ‘Northland’ for containers.
Gooseberries and redcurrants can also grow well in containers, where most fruits require sun to develop a full flavour, both of these bush fruits will grow in some shade. Compact gooseberries include ‘Invicta’, ‘Hinnommaki Gul’ and ‘Remarka’. For red currants try ‘Junkneer van Tets’ or ‘Red Lake’.
It’s time to prune back spring flowering shrubs such as Bachelor Button’s (Kerria japonica), and the flowering currant (Ribes sanguineum) when their blossoms are spent, to tidy them up and allow them put on growth for next year’s flowers. Firstly prune out old and dead wood and crossing or congested stems. For Kerria prune back all shoots that have flowered either to ground level or to a strong side shoot, whilst aiming to maintain an even form. For Ribes, cut back ¼ of the oldest branches. These shrubs can be renovated if they are very old and congested by cutting back all stems to ground level. It seems brutal and not all shrubs respond well to such extreme treatment, which is hardly surprising as they may have reached that point they are old and tired, but many will be revived and will reward the hard shearing with refreshed and invigorated growth.
It can be an onerous job but it’s time to get box hedges, balls, cones, triangles and whatever other topiary forms there are, pruned into shape. It is often a fiddly job as hand shearing is better than a bruising mechanical trimmer but if the trim is kept close to the desired shape it should not need to be done again until mid – late autumn. Best to prune on a still day to prevent the cuttings from flying away before they can be collected.
Box blight is becoming an increasing problem. If your box has succumbed to blight, it may be better to replace it with Ilex crenata or Lonicera nitida that can also be shaped by close clipping.
Early May is a good time to stake or support tall, fleshier herbaceous perennials such as delphiniums and mullein (verbascum sp.) to encourage their emergent foliage to grow through and envelope the supports and create a more natural display. Some supports such as ornamental wire frames and grids or cane and metal wigwams or cloches are positioned to become a focus of a bed, adding visual structure to the scheme as well as support to the plants within it. Either way, without them it is possible that taller plants or flowering stems may collapse or snap in wind or rain and be ruined. It can be tricky to retrospectively stake a flopping plant without making it look restrained and bedraggled. If plants have already leapt ahead and it is too late to stake them it is worth trying to strategically place canes or sticks around the plants so that they have at least a little support. If all else fails it is also possible to cut the offenders back hard to let them grow up again in a more supportive, staked environment yet with time still to flower this year, albeit a little later. Better that than a bed full of collapsed, broken or restrained flowers.
Pollinators are on the wing; bees, ants, hoverflies, butterflies and moths all rely on the nectar of flowering plants for their food. In the process they also pollinate these plants, transferring pollen from one flower to another so fertilizing them and allowing them to reproduce and develop seeds and fruits. Without pollinators, agricultural economies, our food supply and our countryside would fail. Pollinators tend to prefer simple and wild flowers. A succession of flowering annuals, perennials and shrubs can provide nectar and pollen throughout the growing year. Think about planting some plants for pollinators; lavender (Lavandula angustifolia), yarrow (Achillea sp), giant hyssop (Agastache sp), sage (Salvia sp), catmint (Nepeta x frassenii), purple coneflower (Echinacea purpurea) and coneflower (Rudbeckia) can all be planted now. Kept well watered, they will then provide nectar and pollen for visiting wildlife later in the year.
Pests and diseases in apple and pear trees
Powdery mildew is a fungus that forms a white dusty coating on leaves. Good circulation, not crowding trees closely, mulching and watering regularly will reduce stress and make the trees less prone to powdery mildew. A spray made from a mix of 1 tablespoon of baking powder, 1 teaspoon of vegetable oil and 1 teaspoon of liquid soap in a gallon or 4.5 liters of water, sprayed onto the leaves may help if an outbreak occurs.
Raised pink or yellow blisters on the leaves, is a sign of pear leaf blister mite. The tree may look unhealthy but the mite does not impact on fruiting. For local infections the infected leaves can be removed. If the infection has spread widely leave, as the mite will not seriously affect the long-term health or fruitfulness of the tree.
Ponds are a haven for many creatures, supporting large numbers of invertebrates. They provide breeding grounds for amphibians, drinking water for mammals and birds and hunting grounds for bats. Even a half-barrel or old sink, filled with rainwater and a few plants with benefit your local wildlife.
With warmer weather, the water heats up rapidly and it is the best time to plants pond plants, they will quickly fill out. Try water mint (Menthe aquatic), water plantain (Alisma plantago), marsh marigold (Caltha paulustris), flowering rush (Butomus umbellatus) or water forget–me-not (Myosotis scorpiodes). To keep pond water clear and healthy, nutrient levels need to be kept low. Top up your pond using rainwater from a water butt or tank as this is much better balanced than tap water and use only aquatic soil, low in nutrient levels, for your pond plants. Plant native plants rather than exotics. Invasive non-native species can escape into the natural environment and cause havoc with local biodiversity.
Around 50% of the surface of a pond should be free from vegetation. Thin out areas that become overgrown, taking care to leave the thinned plants on the pond’s edge for 24 hours to allow pond creatures to make their way back into the water. Use a twirling stick to remove excess blanket weed and a net to skim unwanted duckweed from the water’s surface. Enjoy watching the watery activities, pond skaters, tadpoles, water boatmen and the local birds and bats that visit your pond.
Gardening tasks in May
- Prune back spring flowering shrubs when they have finished flowering such as Bachelor Button’s (Kerria japonica), the flowering currant (Ribes sanguineum) and Japanese quince (Chaenomeles japonica) to tidy them up and let them put on growth for next years flowers.
- Prune box hedges, balls, cones and triangles into shape. It can be a fiddly job but keep the cut close to the desired shape ideally using hand shears.
- Evergreen hedges can be pruned this month to maintain their health and form. Check first for nesting birds and use hand tools until the end of the breeding season to avoid disturbing them. If you see a nest do not attempted pruning until the fledglings have left.
- Stake or support tall, fleshier herbaceous perennials such as delphiniums and mullein (Verbascum) to encourage their emergent foliage to grow through and envelope the supports. This creates a more natural display. Use ornamental wire frames, grids, canes or metal wigwams depending on the plant and the desired effect.
- Later flowering perennials can be encouraged to have a longer flowering period by giving them the ‘Chelsea chop’. Prune around one third of the stems by a third and another third by two thirds.
- Tie in fast growing climbers such as clematis.
- Thin out annual plants such as sunflowers (Helianthus annuus), Cosmos bipinnatus, and night-scented stock (Mattiola incana), which have been sown in situ to prevent them getting crowded and leggy. Thin out to one healthy seedling per 10-15 cm depending on anticipated growth. If done carefully enough the rejects could be transplanted elsewhere.
- Harden off any seedlings for 10-14 days before planting outside. This means gradually introducing them to cooler and more erratic weather conditions, first leaving them without cover during warmer days and eventually all night till they have acclimatized.
- Continue to deadhead spring flowering bulbs such as daffodil (Narcissis) and grape hyacinth This directs energy to the bulbs for next year’s growth rather than to creating new bulblets from seed. Also feed them with a liquid fertilizer to maintain and improve flowering the following year. Congested clumps can be lifted, divided and replanted.
- Cut back dying allium foliage to keep beds looking spruce.
- After the danger of frosts has passed, sow half-hardy annuals and plant out tender plants such as Dahlias and Cannas and any summer bedding.
- Plant alpine strawberries for fruiting this year.
- Lay a bed of straw around strawberries to deter slugs and net to deter birds but check for any trapped wildlife regularly.
- Transplant indoor seed grown rhubarb to it’s final growing place.
- Weed and mulch fruit bushes, net to deter birds.
- Thin large gooseberries varieties removing every other one and use for cooking, the remaining fruits will grow larger and sweeter.
- Remove unwanted raspberry canes.
- Prune trained cherry and plum trees.
- Cut back leaders and side shoots on mature trained apple and pear trees.
- Hang pheromone traps in apple trees to catch male coddling moths and prevent eggs being fertilized.
- Check apple trees for canker, powdery mildew and scab.
- Check pears for pear leaf blister mite, canker and scab.
- Use a fertilizer such as liquid seaweed on vines.
- Try sowing an area with annual meadow seed, also a boost for pollinators.
- Put out mealworms for blackbirds and robins trying to feed their young.
- Create a deadwood habitat for small invertebrates with mini piles of twigs and stones in beds, great places to hide.
- Fill a hanging basket or open container with sheep’s wool and dried grass for nesting birds to pick from.
- Keep newly planted shrubs and perennials irrigated. Watering in the early morning or evening will reduce water evaporation and therefore the amount of water used. If you haven’t got one, consider installing a water butt to save water.
- Hanging baskets and container grown plants will need increasing irrigation. Do not be fooled into thinking that rain will help. Rainwater is likely to wash away from leaves and over the edge of the container leaving the soil dry.
- Feed container plants every 2 – 4 weeks with a balanced liquid fertilizer such as liquid seaweed to keep them healthy.
- Keep an eye out for any late frost forecasts and protect tender plants with a covering. Bring in or shelter any plants that are hardening off outside.
- Continue to hoe weeds regularly, warm days are best when the weeds quickly dry out and die. Remember that weeds can provide food and habitat for wildlife too, so don’t be too tidy and leave some if you have the space.
- Check for pest and diseases. Viburnum beetle and Lily beetle will start to appear, vine weevils may damage container plants, aphids proliferate and roses may show signs of blackspot. Try to treat with manual or biological methods rather than using pesticides or fungicides that may damage the garden wildlife. Slugs and snails may also be a problem, try nemaslug or wool pellets as opposed to slug pellets.
- Mow lawns weekly. If you would like to try a more wildlife friendly lawn leave a patch to grow longer, clover, daisies and buttercups are likely to appear and support pollinators in you garden.
The New Gardener’s Handbook
A comprehensive guide to gardening: covering soil, propagation, mulching, feeding, pests and more for both ornamental and edible plants.
Recipes for potting soils, fertilizers, pest deterrents and other organic concoctions.
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Things to see, places to go
Due to the Coronavirus pandemic most activities and events have been postponed or cancelled. However many organisations are now posting online activities and events. Here is a selection.
Virtual Chelsea Flower Show
Although the Chelsea Flower Show has sadly been cancelled this year, the RHS are creating an online version to run on the same dates as the show to celebrate our great horticultural industry and gardening heritage with ‘press day’ being Monday 18 May 2020 and the Virtual Show running from Tuesday 19 May to Saturday 23 May. Details to be announced in coming weeks.
19 - 23 May 2020
Urban Tree Festival
The Urban Tree Festival is going online to bring a fascinating, exciting and engaging celebration of urban trees despite the current situation. Organisers have devised a range of activities that you can enjoy from the safety of your own home or during your daily exercise. Some things will be on throughout the festival, these will be online, everyday. Others will be time-limited, live digital events using third party platforms like Zoom. Yet more will be launches of new online resources that will remain online throughout the festival and beyond.
16 - 24 May 2020
There are also a range of online resources and activities, many of which will be helpful for those with children. For example:
South London Botanical Institute
'School visit' programmes and resources for primary school aged children
The Wildlife Trust
A range of downloadable nature resources and activities for children