This Month in the Garden - December
Frost, rainfall and winds are increasingly common, sunshine hours are much reduced and it can be bitter with a risk of snow in December. You may not want to be working outside at this time of year, but luckily there’s not a lot to do. Keep an eye on winter protection and if you have a greenhouse, make sure the heater works.
Sowing and planting:
Alpines can be sown from seed this month. They need a period of cold to break the seed dormancy. A sheet of glass can be positioned over the sown area to protect it from excessive wet. Alternatively, the seeds can be stratified in the fridge, for sowing next spring.
Continue to plant bare-root deciduous hedging plants and trees.
Plant roses, but avoid areas where roses were previously grown as this can lead to problems with replant diseases. Click here to visit our Rose page.
In the greenhouse:
Put up insulating material such as bubble wrap on the inside of the greenhouse, if not already done.
Ensure that there is adequate ventilation in the greenhouse, perhaps opening vents for an hour or two on milder days to encourage air circulation.
Check that greenhouse heaters are functioning properly. Invest in a maximum-minimum thermometer to enable accurate monitoring of the temperature in your greenhouse.
Clear leaves and twigs from greenhouse and shed gutters.
This is a good time to clean all your old pots and seed trays, so that they are ready for next spring’s flurry of activity. Thorough cleaning will reduce pest and disease problems and will reduce your propagation and sowing problems.
Use good hygiene by regularly picking and sweeping up fallen debris to prevent disease re-appearing and spreading.
Cutting back, pruning and dividing:
Pruning and renovation of many deciduous trees, shrubs and hedges can be carried out from now throughout the dormant season. It is easier to see what you are doing when the branches have no leaves. Suitable examples are: Fagus (beech), Corylus (hazel), and also roses. Exceptions are evergreens and tender plants (these are best left until spring) and Prunus species (e.g. ornamental cherries, plums and almonds), as these are vulnerable to silver leaf when pruned in autumn or winter.
Ensure any pruning of Acer and Betula is completed before the end of the year to avoid bleeding of sap from cuts.
Continue to cut back faded herbaceous perennials and add them to the compost heap.
In mild areas, and during dry spells you can still lift and divide herbaceous perennials. This will increase stocks and revive tired or poorly flowering clumps.
Root cuttings can be taken from now. Papaver (perennial poppies), Verbascum (mullein) and Phlox are suitable examples.
Take hardwood cuttings of ornamental shrubs such as Berberis, Buddleja, Salix, Forsythia, Ligustrum and Rubus. Many deciduous climbers can also be propagated in this way (e.g. Fallopia and Lonicera).
Check hardwood cuttings taken last year. They may need planting out or potting on.
Make sure that you have not forgotten any of your tender plants and bulbs – they need to be brought inside or into a heated greenhouse over the winter.
Protect alpines from the wet if you have not done so already.
Large tubs that are at risk of cracking in the frost should be covered with bubble wrap, hessian or fleece, to insulate them over the winter. Plants can be protected with horticultural fleece.
Raise patio containers onto feet or bricks to avoid them sitting in the winter wet.
Tidy up leaves from around borders. They can be added to the compost heap, or placed in separate bins to make leafmould. Some leaves, such as plane and sycamore are slow to break down and can delay you using your compost if you mix them into the general heap. Leafmould makes an excellent soil improver and can also be used as a seed-sowing medium.
Packing the branches of tender deciduous trees and shrubs with straw or bracken and securing this with fleece and ties will protect them from frost.
Remove weeds from around the bases of young trees.
Check tree ties and stakes. Replace, tighten, slacken or remove as necessary.
If there is snow in your area, then you may need to brush it off the branches of conifers, climbers and light-limbed shrubs and trees. Heavy snowfall can splay branches, break limbs and spoil the shape of the tree.
Continue to remove fallen leaves from lawns before they block out light and moisture to the grass.
Grass will continue to grow in temperatures above 5°C (41°F), so if the weather remains mild it may be necessary to use the mower to keep the lawn in trim. Ensure the cut is 3-5mm higher than during the summer to prevent turf stress. On average this means a cutting height of around 2-4cm (1-1.5in) for a utility lawn.
Repair damaged lawn edges or patches with turves cut from other areas of the garden.
Re-cut all lawn edges to crisp up the appearance of the garden, and save work next season.
Avoid walking on lawns on frosty mornings. It can damage the grass and often leads to brown footprint-shaped marks.
Watch your lawn for signs of waterlogging as the weather gets wetter. You may be able to remedy this with some maintenance – either now, next spring, or the following autumn.
If your lawn suffers dieback from treading during the wet, muddy season, then you may wish to lay stepping-stones through it to allow easy access across it without causing damage. Stones can be laid at a low enough level to avoid interference with mowing.
Fusarium patch (snow mould) may be a problem in wet weather, particularly on overfed and lush lawns that have been left a bit too long.
Algae can be a problem on lawns where there is poor drainage, excessive shade, or under the drip-line of trees.
Pest and disease watch:
Garden hygiene helps greatly in the prevention of disease carry-over from one year to the next. It is always a good idea to rake up and burn, bury, or throw away infected leaves. Diseases such as black spot on roses can be controlled to some extent in this way. Do not compost such material, though, as these diseases can persist in compost heaps and re-infect mulched plants.
Damage from bay suckers may still be evident, although the pests will have been and gone. However, it is a good idea to remove affected leaves if there are only a few and to take note to look out for damage next spring (usually around May) – the problem should then be treated promptly.
Phytophthora root rots can cause die-back on mature trees and shrubs. Wet winter weather and poorly drained soils are likely to encourage this problem on susceptible woody plants.
Coral spot is often noticed once the leaves have fallen from deciduous hedges, shrubs and trees. This problem can be connected with poor ventilation and congested, un-pruned twiggy growth (as found inside clipped hedges).
Holly leaf blight is still uncommon, but can be spread in wet weather.
Rabbits and squirrels can be a nuisance as the weather gets colder, gnawing the bark from shrubs and trees. Guards around new woody plants are advisable.
Roses and their surrounding soil can be sprayed with winter washes to help keep black spot under control.
Now’s the time to prune apples, pears, quinces and medlars. If you’re planting new trees and bushes, ensure the ground is not too wet or frosted. Meanwhile, clear late-season debris off the vegetable plots, and dispose.
Prune autumn raspberries.
Prune red and white currants and gooseberries.
Plant new trees and bushes. Don’t plant if the ground is too wet or frosted.
Protect brassicas from pigeons using cloches, netting or fleece.
Remove any yellowed leaves on Brussels sprouts and other brassicas. This will prevent the development of grey mould and brassica downy mildew.
Remove all remaining plant debris from the vegetable plot. Do not compost any diseased material.
Remove any rotten stored fruit.