From the Potting Shed, with Chris Milborne

From the potting shed...

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

December 2024.

December is a busy month in our calendars as we prepare for Christmas. Indoor decorations are enhanced by the colours and beauty of houseplants and the garden is a great source of foliage to create wreathes. Use Holly, Ivy and include evergreen leaves of Elaeagnus, Pyracantha berries, stems of colourful Cornus, evergreen Photinias and Aucuba with their variegated leaves.

The Autumn has been very mild and wet although the last a couple of dry weeks enabled Dahlia tubers etc. to be dug up and the allotment prepared for winter. Whilst lawns have continued to grow, they have simply been too wet to mow.

The December weather can be unpredictable, but gardening, on a cold day can be an invigorating exercise. The last of the leaves have fallen from deciduous trees and shrubs and herbaceous plants have fully died back leaving the garden to revert back to its skeleton. This is a great time to plan any changes you want to make or want to do differently next year.

You can consider extra interest with a new focal point or create or adapt beds and borders. If the garden seems flat, you can add height by using arches and obelisks or using topiary standard lollipop-shaped shrubs such as Holly, Bay trees or Olives. Yew pyramids work really well too. Garden arches and obelisks provide great supports to grow Clematis, Honeysuckle, Climbing Roses, Jasmine or the evergreen Trachelospermum (Star Jasmine) with highly scented flowers in the summer that does best in a sheltered, sunny position. With Clematis, Winter flowering varieties are available and by using different Clematis some flower in Spring, Summer or Autumn so you can virtually have clematis flowers 10 or so months of the year.

Plant an ornamental tree to create a shaded area for next Summer.

Patios can be made more interesting by adding tubs and containers. By grouping together a single style pot you will help this look tidier and less fussy. If conditions allow, dig over and prepare the soil for next year’s planting. You can significantly improve the quality of your soil by adding garden compost, soil improver and well-rotted farmyard manure that all contain the necessary beneficial nutrients for good plant growth - remember the old saying, feed the soil, feed the plant!

As the climate, and therefore weather conditions are changing, it is worth thinking about which plants will best cope with warmer and perhaps wetter conditions. Trees and shrubs will improve air quality and consider the use of ground cover plants as they will provide shade to the soil which helps to retain moisture in the Summer. These plants are also useful in wet conditions as they prevent the goodness from being leached out. Think about the wildlife in your garden as 2024 was disastrous for insects. Add many different types of plants to attract bees, butterflies and other insects by providing flowering plants over a longer period.

December Colour

Despite the soggy brown look - garden colour is provided on even the greyest and dampest of days with the bright coloured stems of Cornus the dogwood, in vibrant reds, greens and the fiery orange of Cornus midwinter fire. The variegated leaf shape of evergreens also adds garden interest especially Pittosporums and Euonymus with a wide range of leaf colours on Coprosma with pink and green foliage, red berries of Cotoneasters and Pyracanthas with glorious colourful red, orange and yellow berries.

Sarcococca has the common name of Christmas Box and is an evergreen shrub, some with purple tinged stems with glossy, green leaves, and in late December into early Spring these leaves are interspersed with fluffy, highly scented white flowers. It likes moist soil in a bright or even in a shady position. The flowers are followed by black berries in late Summer that self-seed easily.

Helleborus Niger or Christmas Rose has beautiful white flowers above leathery green foliage and if you buy at the Garden Centre now it will be in full bloom. However, if you are growing in the garden it will normally flower between late December and February depending on the weather conditions. To guarantee flowers over the Christmas period pot them up in compost with perhaps some added organic matter and grow on in a warm greenhouse.

Other Hellebores are all easy to grow with low maintenance and are good for a shaded location. Many have interesting leaf patterns and are great for adding colour to the garden, particularly in Winter.

Skimmia Japonica Rubella is a small evergreen shrub that thrives in well drained, lime free soil with added compost and produces clusters of pink buds that open in the Spring to produce masses of scented white flowers. Rubella is a male variety and for berries it needs a female type such as Reevesiana to produce bright red berries that last through the Winter.

Pieris is a wonderful plant for growing in a shady, sheltered position and prefers acidic soil. Many produce stunning new red foliage and some form variegated. Many producing white ball-shaped flowers too and it is a shrub great for Winter interest in a container.

Viburnum Tinus is an evergreen shrub with flower buds opening in Spring to produce clusters of white flowers.

Mahonia is an architectural plant with large, leathery, holly-shaped leaves. Some varieties such as Mahonia Caress have softer leaves but it is Mahonia Lionel Fortescue and Mahonia Charity that have the sprays of highly scented yellow ball-shaped flowers. In Winter and Spring, these provide an eye-catching display at the back of the border and the flowers are followed by blue or black berries in Summer.

Ilex Verticillata is a deciduous holly that prefers acidic soil. It has yellow leaves in Autumn and bright red fruits that last well to the Winter.

Gaultheria produces bright red berries and is a dwarf-growing plant useful in tubs and containers.

Ivy

There is an Ivy plant for every situation. You can grow it in pots, tubs and hanging baskets as well as using it for ground cover under shrubs or to cover walls and fences.

Evergreen Rhododendrons, Azaleas, and Camellias are mostly spring flowering but provide rich evergreen foliage. They all require shelter in acidic soil or can easily be grown in containers with ericaceous compost. These look spectacular when planted with Pieris, Japanese Acers with interesting Winter stem colour, Heucheras and grasses.

Hollies

With many cultivated varieties of Holly, the male and female flowers are produced on separate plants and in order to get berries you will need one of each. Always check the labels to ensure you've selected the right variety as the names can sometimes seem a little contradictory with Silver Queen being male and Golden King female.

Ilex Pyramidalis ‘J.C VAN TOL’ is self-pollinating with spineless green leaves and small white flowers in Spring that are attractive to bees followed by red berries for Christmas. You can also find a choice of foliage from variegated silver, golden and deep glossy green. For both berries and golden variegated foliage try Ilex Aquifolium Pyramidalis Aureomarginati or Ilex X Altallerensis, a female variety known as ‘Lawsonia' and produces reddish brown berries. Hollies are adaptable to most soil conditions and are slow growing.

Other plants for interest include Photinias or the architectural leaves of Fatsia Japonica and its cultivar Fatsia Japonica ‘Spiders Web’ with variegated leaves that look fantastic at this time of year.

Plant up decorative outdoor containers to go outside the front door. You can make up attractive displays using flowering shrubs, colourful Pieris, Camellias, Conifers, Heuchera and evergreen Ferns and grasses. Add Winter flowering Heathers, Violas, Pansies and Primroses and some Ivy to trail over the edges. You could also use the colourful stems of Cornus and any gaps can be filled with pot-grown Snowdrops, Crocuses or Dwarf Daffodils and Tulips.

To protect plants that are susceptible to the cold like Agapanthus, Crocosmia and Nerines, apply a good mulch. Raise any tubs and containers on to feet or bricks to improve drainage in wet conditions. Insulate containers with bubble wrap or fleece to prevent compost from freezing, this is especially important for evergreen plants as these all need moist soil conditions to allow uptake of moisture in frozen soil conditions and this can lead to foliage desiccation or drying out. This protection also helps prevent pots from cracking and group planters and containers together.

Grow your own - best for flavour

When you grow your own fruit and vegetables you really appreciate the fresh flavour and effort gone in to growing them. Now, like last month, it is a good time to plant soft fruit trees. Espaliers and cordons can be grown against fences and walls or dwarf fruit trees can easily be grown in large tubs and containers if space is limited. Soft fruit can look great planted amongst other shrubs or in a mixed border.

Start thinking about next year’s seeds whether you're growing vegetables in the garden or allotment or flowers in tubs and borders. Try and grow something a little different each year or look for a completely new plant or go for a different colour scheme.

Now is the perfect time to prune apple and pear trees removing any dead, diseased or crossing branches to maintain an open wineglass shape. After pruning the fruit trees use the twigs next year for pea sticks or supports for broad beans. Alternatively make them into supports for herbaceous perennials to give that natural look.

Prune grape vines before Christmas as this helps to prevent bleeding as the new sap rises in the Spring.

Clean pruners and secateurs between plants to reduce risks of spreading diseases or infections. Lift and divide established clumps of Rhubarb as this reinvigorates plants. A section of root can be used for forcing, producing early crop of tender and sweet Rhubarb.

It might seem a long way off but Runner beans and French beans produce a good and colourful harvest. In preparation create a bean trench or circular hole and start filling this with kitchen waste (veg - not meat) or compost etc. then add a layer of soil. This provides excellent growing conditions for next year. The same procedure can be used where growing Courgettes, Marrows, Pumpkins and Squash next year.

Houseplants

As we retreat inside to avoid the worst of the weather, rooms are brightened by the wonderful colour of traditional houseplants plus the scent of fresh Christmas trees.

A classic Christmas plant is the Poinsettia and its history is as colourful as the plant itself. It originated from Mexico where it grows as a large shrub or a small tree. It was cultivated by the Aztecs for use in medicine and as a dye and from the 17th Century it was used by the Franciscan Monks in Mexico for Christmas decorations. Its name comes from Joel Robert Poinsett a keen botanist and a US Minister for Mexico who introduced the plant to the U.S in the 1820s. In the last 60 years it has become an iconic part of Christmas. The bright colours come from Poinsettias leaves known as bracts and as well as traditional red they are also available in pink, cream, white and variegated while the actual flowers are the small follow tufts in the middle. Poinsettias like bright indirect light in a warm room with an even temperature so avoid placing near radiators or in a draughty position. Keep the compost moist and if possible, use tepid water to avoid root shock.

Cymbidium Orchid is grown for the beauty of the flowers and is one of the most popular orchids to grow with grass-like foliage and stunning large flowers. It is one of the oldest cultivated orchids grown in China for a thousand years. Most Cymbidiums originate from the forests of China, Japan, Korea and Himalayas and is one of the easiest indoor orchids to grow with flowers lasting up to 8 weeks.

Orchids flourish in a kitchen or bathroom with good light, stand the pot on a saucer of damp pebbles for extra humidity. From June to September Cymbidium Orchids can be kept outside under a tree where they receive dappled sunlight. Add orchid fertilizer when watering every 2-3 weeks. Arching spikes of flowers found on the favourite orchid and houseplant Phalaenopsis also known as the Moth Orchid flowers last for between 6 to 8 weeks and they are repeat flowering virtually the whole year with arching spikes of pinks, creams and white flowers. They are native to India, China and South East China where they grow in trees and this is why these orchids are grown in clear pots allowing light to reach the roots.

Other interesting orchids available are the Dendrobium the ‘care orchid’. Orchids should be watered with rain water or boiled tap water (cooled) as they don't like chlorine or chalk. Be sure not to over water.

Be careful not to overwater Christmas Cacti flowers from late November to late January. These give a wonderful Christmas display or make an ideal gift. This is a forest Cacti growing on trees in jungles of S. E. Brazil and it requires a well Iit spot with damp compost to produce stunning flowers in pink, white or reddish shades. Once the flower buds start colouring up and opening don't move the pot to a different position as this can cause the bud, to drop.

Other favourites include stunning Azaleas, large flowered Cyclamen both these require cooler growing conditions and the highly scented white flowers found on Jasmine Polyanthum.

Citrus

Citrus Meyers Lemon are self-fertile, with fragrant white flowers tinged purple. During the Summer months they are ideal for growing in containers on a patio. Winter care as with all Citrus require a light, bright position in cool conditions with the compost just damp. In warm, centrally heated rooms they have a tendency to shed leaves.

TIP - Remember with all flowering plants or even bunches of flowers don't place them next to the fruit bowl as the gas Ethylene, given off by the ripening fruit (especially bananas) causes the flowers to go over quickly.

Wishing you all a happy peaceful Christmas and New Year and look forward to the 2025 gardening year.