April Hints & Tips

From the potting shed...

Our monthly gardening newsletter, written by our Great Amwell plant department colleague, Chris Milborne.

April is definitely one of the most exciting months in the garden. The longer days, warmer weather and increasing sunlight means you will see more changes now than at any other time of the year. Leaf buds on the branches of trees and shrubs are followed, as the month progresses, by bright green leaves unfurling each day and by the end of the month there will be the green, yellow, pink and purple of fresh new leaves over your trees and shrubs. The beauty of springtime in the garden, parks and the countryside cannot be beaten.

Flower beds and borders which a month ago were just empty wet brown areas of soil are now full of growth and the flowers of early Spring Bulbs and the new shoots of Herbaceous Perennials. These are some of our best known and loved plants and flowers in beds, borders or used in containers and include; Lupins, Delphiniums, Penstemons, Phlox, Oriental Poppies and then later summer flowering Salvias, Echinacea, Helenium, Coreopsis and Rudbeckia. A Herbaceous Perennial is generally a non woody plant that grows year after year, flowers and dies down in the winter to dormant roots, although there are some exceptions. Some are evergreen such as Bergenia, Hellebores, many Euphorbias, Flag Iris, Kniphofias and Heucheras. Heuchera is wonderful plant with leaves in many colours from lime and marmalade to purples and pinks. They are virtually indestructible and grow almost anywhere.  

Some perennials like Hollyhock or Delphinium begin to fade after 5 years or so and others such as Peonies (Paeonia family) may last a lifetime. Many Herbaceous Perennials, after 4 to 5 years, will benefit from being lifted, divided and replanted whilst incorporating some compost and feed. This will give them a new lease of life. Herbaceous Perennials are such a wonderful and diverse group of plants for the garden. Originally, in the 19^th Century, large herbaceous borders were created but today’s smaller gardens have to work harder to provide more interest over a longer period.  Selecting Herbaceous Perennials for mixed borders together with Annuals, Biennials, Shrubs, bulbs, Roses and autumn & winter interest plants will reward you with stunning year-round displays. An important consideration when designing the area is how plants are arranged so that later flowering or foliage plants hide the gap left by earlier flowering bulbs and plants. I use them to hide the foliage of Alliums or the dying leaves of Daffodils that can look untidy. For added impact consider the colour wheel when designing your space. Many herbaceous plants have great foliage and may provide interest over a long period with silver, gold, purple, or variegated leaf varieties making for excellent additions to plants grown in tubs and containers too.

Tulips are starting to look sensational and as Daffodils fade give them a feed to produce healthy bulbs for next year. Remember to let bulbs die down naturally, so all that energy returns to the bulb, underground. Sweetly scented Wallflowers in many colours are now in full flower along with trees full of blossom, depending on weather conditions, especially the glorious flowers of Japanese Ornamental Cherries. In Japan “Hanami” is an age-old tradition celebrating the stunning blossom by having parties under the tree canopies. Perhaps we won’t have the weather here but never the less we can enjoy the beautiful blossom. Possibly some of the best Prunus varieties include ‘Royal Burgundy’ with its rich purple leaves and rose-pink double flowers. Prunus ‘Beni-Yutak’ gives added interest when the pink tinged flowers open fully to reveal pure white blossoms. ‘Fragrant Cloud (Shizuka)’ has glorious large white semi double flowers and ‘Amanogawa’, the Flagpole Cherry, delights with semi-double light pink blooms. For a very small garden, or even a large container, the dwarf Cherry Prunus ‘Snow Showers’ has spectacular single white flowers on pendant branches. Another small weeping tree is Prunus Pendula ‘Shidare-Zakura’. It’s one of the oldest cultivars with beautiful double rose pink blooms. In a large garden the Prunus ‘Taihaku’ (the Great White Cherry) became rare in Japan before being reintroduced from the UK in 1932 having been grown by the Cherry enthusiast Collingwood ‘Cherry’ Ingram, who is also an ornithologist. 

Other tree highlights include Apples, Pears, Plums and fruiting Cherries. As well as glorious blossom the fruit they provide can easily be grown even in small gardens with varieties on dwarf root stock suitable for large pots or containers.

Crab Apples (Malus) are stunning trees with white, pale pink to pink cup shaped flowers. Perhaps longer lasting than Ornamental Cherry blossom these trees have the added interest of diverse colour fruit enjoyed by wintering birds and the beautiful autumn leaf colour makes this a tree for many seasons. They will thrive in a sunny spot with fertile soil.

Other April highlights include Spiraea ‘Arguta’ a reliable shrub that almost disappears under a covering of tiny white flowers at this time of the year. It is very easy to grow and withstands all weathers. Other Spiraeas, such as ‘Magic Carpet’, show off wonderful new leaves that open orange before maturing to yellow. Perhaps not such a well-known shrub is Physocarpus. The wonderful foliage of ‘Magic Ball’ changes from vibrant orange to yellow/green. ‘Opal Midnight’ has maroon foliage and ‘Lady in Red’ with it’s reddish/purple hues is simply stunning. Many Physocarpus also have interesting bark and they perform best in a moist, but well drained soil, in full sun or partial shade. When planting remember to water well until roots have established, this normally takes around 3-6 months. Using Bonemeal when planting, helps roots to grow.

Ribes ‘Sanguineum’, the flowering currant, was used in medieval times as a cure for lung disease. The cascading strings of reddish pink flowers or white flowering varieties have blackcurrant scented foliage and are very easy to grow.

For sheltered areas protected from hot summer sun or cold winter winds, Japanese Acers cannot be beaten. With unfurling green pinky orange foliage at this time of year they make a good companion to spring flowering Camellia, Rhododendrons, Azaleas and Pieris too. Pieris has young red foliage plus sprays of white bell-shaped flowers. Other good plants for April interest include Berberis darwinii, Magnolia x Soulangeana (with large pale pink Tulip-shaped flowers), Kerria Japonica, Viburnum, Mahonia and Herbaceous Perennials like Doronicum, Pulmonaria, Helleborus and Bergenia.

By the end of the month pale pink scented flowers of Clematis Montana will open; a beautiful sight covering fences, trellis and walls.

April is a good time to plant Roses. Every garden should grow a few Roses with their abundant fragrant flowers in the summer transforming flower beds and borders. Climbing and Rambling Roses are good for covering bare walls or fencing or allow Rambling varieties to climb up through trees for extra interest. The Rose label will indicate if the plant is scented and repeat flowering or if flowering once is to be expected, as with species types. Many will produce wonderful colourful hips in the autumn provided faded flowers are not dead-headed. Our warm and wet autumn together with a wet winter may make Roses slow to start into growth this spring having possibly suffered some die back.  Don’t worry. Trimming back to a healthy bud and feeding with a Rose feed, or ‘Fish Blood & Bone’ fertilizer, will encourage the plant to send out healthy new shoots.

April is a good time to put plant supports around Herbaceous plants before they grow too large. I tend to leave these in position year-round as a reminder, in the dormant winter months, of where I have planted. This helps minimize disturbing the soil and damaging the roots when planting bulbs or other plants. When Daffodils die back the holes left by decaying foliage should be filled with soil as this helps prevent insects entering and damaging the bulbs.

Patios and Containers

As spring progresses the earliest spring bedding fades but as the season continues more and more colourful plants become available. Really wonderful and inspired containers can be planted up or purchased ready-made.

A useful addition for instant impact is Senetti; bred as a houseplant many years ago, today, with many hybrids available, they will tolerate a light frost. Senetti have brightly coloured Daisy-like flowers appear in vivid pinks, blues, reds and purples above soft heart-shaped leaves. The plant is native to the Canary Islands growing in forests and rocky cliff tops. Best treated as an annual and kept frost free, the flowers should continue into early summer. This can be encouraged with regular dead-heading and feeding with a liquid tomato food.

When planting up containers it is best to discard old compost. This can be used as a mulch around plants in the border or as a lawn top dressing. Using fresh compost helps break up the life-cycle of overwintering pests such as vine weevil.

Create a wildflower garden. Choose a range of different wildflowers or sow from seed. By growing various plant species, the flowering period may be extended which will in turn, will offer food for more pollinating insects. Bellflower, Cornflower, Knapweeds, Oxeye Daisy, Wild Carrot, Marjoram, Mallow, Meadow Cranesbill and Scabious are all worth considering.

Lawns

With all the winter rains lawns have taken a hit with moss and compacted surfaces. Now is the time to treat moss and weeds as well as feed the lawn. This greens up the grass and helps it to compete & beat any weeds and mosses. It is also a good time to re-seed any bare patches and straighten the lawn edges as this makes the garden look neat and tidy, and repair any dips and hollows.

If not completed in March, all plants in the garden will benefit hugely with a feed of fertilizer such as Fish, Blood and Bone or Vitax Q4.

Fruit, Vegetable and Herb Garden

April in the vegetable garden is the month of non-stop propagation or planting for the summer vegetables. Sowing, growing, potting and transplanting, all take place during April.

Make seedbeds.

Cover beds with cardboard to keep down weeds prior to sowing.

Mulch beds with organic matter to retain moisture.

Keep on top of weeds as soon as they emerge.

Use cloches to protect early crops.

Put up supports for Peas and Beans.

Plant out Onions growing in modular trays planted earlier.

Plant 1^st Early, 2^nd Early and Maincrop Potatoes. Earth up any early shoots to minimize the risk of damage by late frosts. 

Sow Broad Beans, Peas, Summer Cabbage, Brussel Sprouts, Beetroot, Carrots, Parsnips, Leeks, Spring Onions, Turnips, Spinach, Chard and Sprouting Broccoli. In the cold frame I sow Lettuces. Sowing a few seeds every 2 weeks for cropping over a longer period helps to avoid getting a glut of produce. I grow on and plant out good strong established plants which will be less prone to damage caused by slugs and snails.

Rocket, Radishes, Turnips, Kohl Rabi and Cabbage are best sown under fleece or ‘Enviromesh’ (a plant protection netting) to minimize Flea Beetle damage which is often a problem if Rape Oil Rape is grown in near-by farmers’ fields. 

In a frost-free greenhouse, cold-frame or grow house sow frost tender veg such as Cucumbers, Dwarf French and Runner Beans, Sweetcorn, Marrows, Pumpkins, Squashes, Courgettes and Pumpkins – these last 5 sown on their side, not flat, to prevent rotting prior to germination.

In a propagator sow Tomatoes and Melons for growing in a greenhouse. Tomatoes can be grown outside, June onwards.

We have a huge range of vegetables available ‘Ready to Plant’ in strips or pots, if you don’t have time to sow seeds, or just don’t wish to wait.  All of these are easy to grow and can be planted in ‘Gro Bags’ or tubs and containers. If you have a small garden, or just a patio or small space, you can still easily have a go at growing your own crops. Home grown plants often produce far tastier & juicier vegetables.

Herbs

Herbs have traditionally been used in medicines and for flavouring foods, for generations.

Earliest records go back to 2,000 BC in Babylon; many originating from the Mediterranean and Middle East. Herbs are often easy to grow in free draining soil and a sunny position and this helps to intensify the oils within the plant, improving their flavour. Grow on windowsills, in containers or herbaceous borders near to the BBQ, ready for use in the kitchen. Picking and trimming regularly helps the plant produce fresh new growth.

Sow hardy herbs such as Parsley and Coriander little and often so as to keep a good supply even if some plants run to seed. Add plenty of organic matter to the soil when planting out Chives, Parsley, Fennel, Dill and Lemon Balm, as they are all hungry plants. Lemon Balm is a very good insect repellant – useful when having a BBQ.

Divide up established clumps of Chives and replant in rich, moist soil in a sunny position. Sow Basil seed indoors during April for planting out in May or June as these plants are prone to rot in cool conditions, or fail, during the final light frosts of the spring.

Sow annual flowers such as Nasturtiums, Marigolds and The Poached Egg plant (Limnanthes), amongst Herbs, Vegetables and Soft Fruit too, as they help to attract friendly predators, which, in-turn helps to keep pests at bay. 

Pot grown Herbs are always available to buy and make for stunning patio container displays. In a sunny spot, grow Lavender, Rosemary, Marjoram, Oregano and Sage with Thyme cascading over the edges. For a shady spot Parsley (flat leaved or curly), Mint, Dill, Chervil and Coriander all do well. Plus adding a few flowering Marigolds for colour.

Fruit

Feed Blackcurrants, Blackberries, Gooseberries, Raspberries and White & Red Currants. Feed Blueberries with an Ericaceous feed, ideally.  

Planted up Strawberries do well in containers or hanging baskets. Creating Soft Fruit areas, perhaps in large tubs or containers, can save money too, as you won’t need to buy them! Also Great for lovely summer puddings.

Modern methods mean fruit growers can now supply dwarf rootstock varieties.

Peaches, Nectarines, Apples, Pears, Cherries and Plums can all be easily grown in any sheltered sunny position, for wonderful fruit.

After the mild, wet winter watch out for Slugs and Snails. Take necessary precautions & keep on your guard for any late frosts (have some protective fleece handy)!

Generally, all chance of frost has passed by middle to late May, but often in recent years, it has been earlier due to our changing climate.