Winter Gardening

Slug

Slug, Peter McDermott, CC BY-SA

A mild and very wet November has left soils waterlogged. The lack of frosts has meant leaves and some colour remain but many plants have collapsed after being battered by the rain. Pests such as slugs and snails have continued to be active as the weather is still warm and both viruses and bacteria persist, not yet subdued by winter’s cold. Very wet soils can be damaged by active cultivation though the mild, damp conditions are good for planting. Any pruning should be left until a clear, frosty day as mild, damp conditions increase the possibility of disease entering a plant through the cut.

December is a time for reflection. Chilly, crisp and dark days herald the true beginnings of winter. The bare bones of the garden are exposed. Few leaves and fewer flowers, allow the structural plants to dominate. Evergreen plants, strong winter stems and attractive barks can bring welcome colour to an otherwise quiet, grey scene.

In the garden

Acer griseum

Acer griseum, Evelyn Simak, CC BY-SA

Trees with ornamental bark, often hidden by strong leafy growth the rest of the year, can shine in the winter and add to the year round interest of a garden. Paperbark maple (Acer griseum) with its flaky peeling bark shining a rich yellowy orange; coral bark maple (Acer palmatum ‘Sango-Kaku’) with deep pink stems; Himalayan birch (Betula utilis var. jacquemontii) with brilliant white bark; Tibetan cherry (Prunus serrula) with a rich red glow in low light; and river birch (Betula nigra) with peeling grey-white bark becoming pinky orange in the wintery sunshine.

Shrubs too can display colourful stems in winter: dogwood, willow and bramble all have many varieties with brilliant coloured barks. Rubus cockburianus has a ghostly white bloom over arching purple stems, Cornus alba ‘Kesselringii’ has deep purple black stems and Cornus sanguinia ‘Midwinter Fire’ has stems which from base to tip change through yellow, orange and red to pink. Willows grow well in damp soils, Salix ‘Yelverton’ has orange yellow stems and Salix alba var. vitellina ‘Britzensis’ vivid scarlet stems.

Holly and mistletoe, the characteristic Christmas plants, are favorites in December. Mistletoe is a semi parasitic shrub that grows on other trees, taking water and nutrients from the host. The seeds are sticky and dispersed by birds that either smear off the remains or excrete droppings onto a branch. The seed grows roots, which pierce the bark and feed from the tree, growing into rounded balls, clearly visible on the bare branches in winter.

Holly (Ilex aquifolium)

Holly (Ilex aquifolium), Ashley Dace, CC BY-SA

Hollies or Ilex have a variety of leaf colour, shape and berry colour. Male and female flowers are grown on separate plants, so to be sure of fertilisation and colourful berries you will need to plant one of each sex close together. Ilex aquifolium ‘Handsworth New Silver’ has dark green leaves, edged with cream and bright red berries, Ilex aquifolium ‘Pyramidalis Fructu Lutea’ has dark green leaves and yellow berries. Ilex x altaclerensis ‘Golden King’ has oval variegated leaves with large red berries, Ilex x altaclerensis ‘Lawsoniana’ has green leaves with central splashes of yellow and pale green and bright red berries.

Red admiral on Ivy

Red admiral on Ivy, Dave Dunford, CC BY-SA

Evergreen shrubs give interest and provide welcome shelter for wildlife in the cold months. Denser shrubs will provide the best shelter. Lauristinus (Viburnum tinus) has shiny, dark green leaves, clusters of pale pink flowers throughout winter, followed by black berries. Ivy is useful protection for both insects and birds, it can provide nectar as late as December and its winter fruiting berries provide food for blackbirds and thrushes as well as hibernation sites for butterflies.

Planting fruit trees

Winter flowering cherry tree at Glasgow airport

Winter flowering cherry tree at Glasgow airport, Thomas Nugent, CC BY-SA

Once you have selected fruit trees for flavour, locality, eventual size and pollination group (see our November blog post), it is time to prepare the ground and plant, allowing strong root systems to establish before the spring and new growth arrives. Bare root apples and pears can be planted until March, cherries and plums until January. Ideal planting times are when the soil is moist and warm so neither frozen nor very wet.

First clear the ground around where you are planting of any annual and perennial weeds or grasses, digging them out by the roots. Dig over a meter square to the depth of the tree’s root system, checking the eventual soil level will be the same as the soil mark on the trunk. Remove the tree from the pit and drive in a strong stake with a sledgehammer, this needs to be buried by around 60cm to provide support for the growing tree, preventing wind rock and movement of the roots that can damage the root system. The stake can either be upright or at 45 degrees to the ground. Soak the root ball briefly to dampen the roots and replace in the pit, jiggling it to settle it and turning the tree to arrange the branches to form a pleasing shape when viewed from the front. Back fill the hole while lifting and shaking the soil to make sure all air pockets are filled, tamp down gently with your heel but without compacting the soil. Tie the tree to the stake with a belt tie that is close to but separates the tree from the stake. The tie should be placed on the trunk at 1/3 of the height of the tree. Water the tree in well and mulch with well-rotted stable manure or garden compost.

Winter pruning apples, pears, currants and gooseberries

Tree pruning, Omagh

Tree pruning, Omagh, Kenneth Allen, CC BY-SA

Many people are apprehensive of and confused by pruning, but with sharp secateurs, loppers and pruning saws, and frequent checks on the overall shape, it’s not a difficult task. The aim in pruning bush or standard fruit trees and currant bushes is to create an open, vase shaped form where air can freely flow between branches and stems, to increase fruiting, to help prevent congestion and the potential build up of disease.

For all trees and bushes begin by cutting out the crossing, dead, damaged and diseased wood. For apples and pears, next shorten the previous year’s growth on the main branches by one third, leaving the laterals that grow off the main branches unpruned to develop fruiting buds the following year. Finally cut out shoots growing towards the centre and any crossing or congested side shoots. Older trees develop fruiting spurs; short, woody growths on the tips of branches, thin these out if they become congested.

The winter pruning of gooseberry, red and white currant bushes is the same. As with the trees, cut out crossing, dead, damaged and diseased wood. Next prune all side shoots to 1-3 buds from the base of the stem, finally shorten the branch tips by around ¼ cutting back to an outward facing bud.

Planting deciduous trees and shrubs

Silver birch (Betula pendula)

Silver birch (Betula pendula), Mike Kirby, CC BY-SA

December is a good time to plant deciduous trees and shrubs but don’t plant when the ground is waterlogged or frozen. As with planting fruit trees, soil preparation is key to healthy establishment and growth so spend time getting this right. First dig over the soil to the depth of the rootball and over about 1 meter square, at this stage you can incorporate some well-rotted stable manure to improve the soil structure. Tease out the roots of containerized plants and spread out the roots of bare root plants. Dig the hole to the depth of the roots and about three times the width of the spread. Soak the plant or pot well for 20-30 minutes before planting. Place the tree or shrub in the hole making sure that the root flare area will be level with the top of the soil. For larger or heavy trees and shrubs a stake may be necessary to prevent the plant toppling over as it establishes, hammer this in before final positioning. Fill in the hole, making sure to lift and shake soil between all the roots and tamp down gently to fill any air pockets. If a stake has been used tie the plant securely to the stake in an upright position.

Planting hedges and trees to trap pollution

Yew hedge, Powis Castle

Yew hedge, Powis Castle, Rosser1954, CC BY-SA

If you live in a heavily polluted area, planting suitable trees and shrubs that can trap pollution can be very effective in freshening the air. Planting street trees, beside a playground, food growing area or front garden can help by removing some of the pollution from the local environment. Plants collect polluting particles on their surface areas, particularly evergreens with rough leaves or dense canopies. Hedges, and densely planted shrubs, mixed with trees, create the best pollution barriers. Plants like yew (Taxus baccata), lauristinus (Viburnum tinus), western red cedar (Thuja plicata), cotoneaster, hornbeam and whitebeam (Sorbus aria) have been shown to work well.

Making Compost

Compost

Compost, Lucabon, CC BY-SA

For anyone that has the space, making compost is an essential part of helping to create and maintain a fertile soil. Well made compost, spread on or dug into the soil is full of microbial activity making nutrients available to growing plants and helping to maintain a good, open soil structure with the correct levels of moisture and air. Compost improves permeability, aeration and drainage and increases resistance to erosion, while boosting nutrient availability.

Slow, cold compost making is the simplest method in small spaces. ‘Green’ and ‘brown’ materials are added to an enclosed heap, the heap is kept moist and slowly over a year the waste material turns to compost. Building or buying a bin will retain warmth and moisture more easily than using an open heap, making better compost more quickly. Very simple bins can be made from four recycled pallets tied together with wire, the sides lined with cardboard or stuffed with straw or hay. The top can be kept covered with cardboard to retain heat. Bins of 1 meter square or larger work best.

Use greens and browns at a ratio of 1:2 by volume in layers.

Greens

  • Kitchen Waste
  • Animal Manure
  • Green Prunings
  • Grass Cuttings
  • Comfrey
  • Seaweed
  • Young Weeds/ Nettles
  • Urine
  • Coffee Grouns

Browns

  • Autumn Leaves (not too many) - they can be made separately into leaf mould.
  • Mature Weeds/ Nettles. NB: No seeds or perennial roots!
  • Mature Grass. NB: No seeds!
  • Cardboard – especially corrugated
  • Paper – shredded/screwed up
  • Straw
  • Woody Prunings - shredded
  • Thin Twigs/ Stems
  • Hedge Trimmings

Don’t put diseased plants onto the heap as the disease may recur when the compost is later put onto the soil, these can be bagged and recycled at your local recycling centre where the high temperature of their composting facilities will kill viruses and bacteria. Seeds may not be killed by the slow method so cut off any weed seeds before composting, perennial weed roots may also survive so put them aside. Cooked foods, fish and meat may attract vermin so they should be avoided.

If the heap appears too dry, add water, close any gaps and cover the top with plastic. If the heap is too wet or smelly turn it and add some dry materials such as hand sized bits of corrugated cardboard. If it is very slow to decompose check the moisture level and add urine or animal manure (guinea pig and rabbit bedding or stable manure works well.)

Once the compost is ready spread it on the surface or fork in lightly, earthworms will draw it down, their activity improving soil structure and aeration.

Plant propagation, hardwood cuttings

Hardwood cuttings taken in December will provide new plants, ready to be planted out by next autumn. At this time of year you can take cuttings from both deciduous and evergreen woody plants.

Chose strong and healthy looking woody stems, about the thickness of a pencil. When taking cuttings from deciduous shrubs wait until the stems are bare, make a horizontal cut just below a node at the base - the place where the stem widens and new leaf buds are beginning to show- and a diagonal sloping cut just above a node around 20cm further up the stem. Evergreen cuttings are taken in the same way, before removing the leaves from the lower half of the stem.

The cuttings can be grown on either outside in a trench or in pots. First prepare the soil. Outside, add sand to the soil, to create a well-drained growing medium and make a slit wide trench, or fill deep pots with a half and half mix of multipurpose compost and grit. Dip the cut bases into a hormone rooting product and insert in the trench or pot. Insert around ¾ of a deciduous stem and around ½ of an evergreen stem in the soil. Keep pots in a sheltered spot or cold frame and firm in well. Water gently at first but make sure the cuttings are kept well watered as the weather becomes warmer and drier in the spring and summer.

Pruning trees and shrubs prone to ‘bleeding’

Lime tree's winter silhouette

Lime tree’s winter silhouette, Dan, CC BY-SA

Sap carries nutrients and water through a vascular system to all parts of a plant. Some plants bleed profusely from pruning cuts or wounds. In most deciduous plants the sap production decreases in autumn and winter as the plant becomes dormant, in late winter and early spring the rising sap carries nourishment to the swelling leaves and buds. There are some plants where the sap starts to rise early, leaving them vulnerable to excess bleeding during late winter pruning. For those it is best to prune earlier in the seasonal cycle, in December.

Trees and shrubs that benefit from December pruning include grape vines (Vitus), maple (Acer), walnut (Juglans), birch (Betula), mulberry (Morus) and lime (Tilia). Choose a cold, bright day and head out with clean, sharp secateurs.

Gardening tasks in December

Woody Plants

  • Plant deciduous trees and shrubs.
  • If there is snow, shake it off trees and shrubs to prevent the extra weight bending and breaking branches and stems.
  • Check the condition, ties and stakes on any newly planted trees and shrubs.
  • Prune plants prone to bleeding from cuts such as maple (Acer) and birch (Betula).
  • Plant shrubs with winter fragrance such as sweet box (Sarcoccoca confusa) close to a path or entrance to lift the spirits.

Ornamentals

  • Check the condition of any plants needing winter protection.
  • Prune climbing roses and ornamental vines.
  • Take hardwood and root cuttings.
  • Plant bare root roses.

Fruit

  • Prepare new ground and plant new fruit trees, bare root cherries and plums until January, and apples and pears until March.
  • Plant bushes and cane fruit until March.
  • Prune established apple and pear trees for shape and fruiting, remove dead, damaged and diseased branches.
  • Prune gooseberries and currants, it is easier to shape the bushes once the leaves have fallen.
  • Prune grapes vines before Christmas and the rising sap.
  • Weed around the base of fruit trees, bushes and cane fruit and mulch with well rotted stable manure or garden compost.
  • Check tree stakes, ties and the supports of trained trees.

Wildlife

  • Provide food and water for birds, make sure feeders and bird baths are cleaned regularly and clear of ice.
  • Make a hole in icy ponds with a kettle of hot water to provide oxygen to the water and a place for mammals and birds to drink from. Don’t smash the ice as this can harm some pond living creatures.

Sustainable Practices

  • Leave perennials uncut, the stems will provide hibernation sites for beneficial insects.
  • Wash, dry and stack your seed trays, pots and unused containers ready for the spring planting season.
  • Put bird feeders near plants with that may be harboring overwintering pests. They can be picked off while the birds are waiting their turn at the feeder.
  • Cut stems of evergreens, dried flower and seed heads and stems with berries to make sustainable festive wreaths and decorations.
  • Protect non-frost proof pots by bringing them into the house, a shed, or sheltered place or wrapping in straw and hessian.

Relaxing reading

A Modern Herbal

A Modern Herbal

Alys Fowler

Plants, their healing properties and how to use them written in an accessible and engaging style.

Buy >

Scent Magic: Notes from a Gardener

Scent Magic: Notes from a Gardener

Isabel Bannerman

Poetic descriptions of fragrant plants, personal memories and practical information to scent in the garden throughout the seasons.

Buy >

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Things to see, places to go

Foraged Festive Florals

Making sustainable floral, festive decorations.

date

6 December 2019, 10.30am - 12pm

location

RHS Garden Wisley, Wisley Lane, Woking, Surrey, GU23 6QB

Learn more >

Glowing Garden Party

Illuminated winter botanical garden with music, dancing, food and drink.

date

10 December 2019, 6pm - 8pm

location

The South London Botanical Institute, 323, Norwood Road, London SE24 9AQ

Learn more >

Catriona Andrews

CATRIONA ANDREWS

Catriona is a landscape designer and environmental educator. Her work combines naturalistic planting and sustainable practices to create spaces that are sensitive to the environment and welcoming to wildlife. She designs private gardens, community gardens and public spaces and leads courses and workshops on garden and planting design and the environment.