December is the first month of summer, and with the warmer weather gardens explode into life, becoming lush, abundant and awesome to behold. With the days getting longer as we progress towards the longest day of the year, the summer solstice, there’s more time to enjoy the garden and the great outdoors!
During this month of warm sunny days, temperatures can reach extremes, with the threat of bushfires arising during dry, windy periods.
Weather can be variable in December, and summer thunderstorms may bring wind, heavy rain and hail in some areas.
In Canberra, this is the windiest and sunniest month of the year, with Canberra averaging 9 hours of sun per day.
At this time of the year the risk of frosts has passed, though in Tasmania, the temperatures at Mount Wellington can fall to 0°C.
During the summer heat, gardens can get quite dry, so keeping up with the watering is important. Pests will also emerge with the warmer weather so keep an eye out for them!
‘Chop & Drop’ any broad beans or peas after harvesting – chop the tops at ground level, and drop them on top of the soil as mulch, leaving the roots in the ground to return any nitrogen in the root nodules to the soil. Cover with any mulch to keep things looking tidy.
It may seem unusual, but early summer is also the time to sow some winter brassicas such as broccoli, brussels sprouts, cauliflower and swedes, so they can be harvested in winter.
Things to Do This Month:
- Top up or add extra mulch around fruit trees and plants to retain soil moisture and reduce water loss from evaporation. Keep mulch away from plant stems and tree trunks to prevent collar rot.
- Propagate climbers by layering, and propagate strawberries by pegging down runners onto the soil.
- Propagate plants by taking softwood (green) cuttings from now till January (after which they begin to harden off).
- Last chance to plant potted fruit trees and vines to beat the summer heat (having roots, they can be planted anytime, but best in spring & autumn). Pick a day when the weather is mild!
- Continue tying growing vines and brambleberries such as blackberries and their hybrids back to supports or wires.
- Thin out fruit on plum trees if there is a risk of branches breaking.
- Last chance to plant tomatoes and capsicum seedlings.
- This is an ideal time to add new fish to ponds or water gardens, as they acclimatise easier in the warmer weather.
Vegetables and Herbs to Grow in December (Cool & Alpine Climate)
| December Seeds to Sow and Seedlings to Plant (Cool & Alpine Climate Australia) | Sow/Plant | Harvest (weeks) |
| Amaranth | dst | 7-8 |
| Angelica | t | 18 months |
| Asparagus Pea | d | 8-11 |
| Basil | st | 10-12 |
| Beans (Climbing) | dst | 9-11 |
| Beans (Dwarf, Bush) | dst | 7-10 |
| Beetroot | dst | 7-10 |
| Borage | dst | 8-10 |
| Broccoli | st | 10-16 |
| Brussels Sprouts | st | 14-28 |
| Burdock | d | 17-18 |
| Cabbage | st | 8-15 |
| Carrot | d | 12-18 |
| Cauliflower | st | 15-22 |
| Celeriac | t | 14-28 |
| Celery | t | 17-18 |
| Chicory | st | 16-24 |
| Chinese Cabbage | st | 8-10 |
| Chives | dst | 7-11 |
| Collard Greens | dst | 8-11 |
| Coriander (Cilantro) | dst | 4-6 |
| Cucumber | dst | 8-10 |
| Daikon | d | 8-10 |
| Dill | dst | 8-12 |
| Endive | dst | 10-11 |
| Fennel (Florence) | dst | 14-20 |
| French Tarragon | t | 30-40 days |
| Globe Artichokes | t | 42-57 |
| Horseradish | plant crowns | 16-24 |
| Jerusalem Artichokes | plant tubers | 15-20 |
| Kale | dst | 7-9 |
| Kohlrabi | dst | 7-10 |
| Leeks | dst | 15-18 |
| Lemon Balm | dst | 8-10 |
| Lettuce | dst | 8-12 |
| Luffa | dst | 11-12 |
| Marrow | dst | 12-17 |
| Mint | dt | 8-12 |
| NZ Spinach (Warrigal Greens) | dst | 8-10 |
| Oregano | dst | 6-8 |
| Parsley | dst | 9-19 |
| Potato | plant seed potatoes | 15-20 |
| Pumpkin | t | 15-20 |
| Radish | d | 5-7 |
| Rocket | d | 21-35 days |
| Rosemary | d | 12 months |
| Sage | dt | 18 months |
| Salsify | d | 14-21 |
| Silverbeet (Swiss Chard) | dst | 7-12 |
| Spring Onions (Bunching Onions) | dst | 6-10 |
| Squash | dst | 7-8 |
| Summer Savory | t | 6-10 |
| Sunflower | t | 10-11 |
| Swedes (Rutabaga) | s | 10-14 |
| Sweet Corn | st | 11-14 |
| Thyme | t | 42-52 |
| Tomatillo | dt | 10-14 |
| Tomato | t | 8-17 |
| Turnip | d | 6-9 |
| Winter Savory | t | 6-10 |
| Zucchini (Courgette, Marrow) | dst | 6-9 |
Key:
d = sow seeds directly into ground
s = sow seeds into seed tray
ds = sow seeds directly into ground or seed tray
t = transplant seedlings (small plants) into larger pots or plant into ground
*= frost tender
**= sow after frost
Download printable PDF version of Gardening Calendar (Australian Cool & Alpine Climate) – December
To help improve these garden calendars, feedback and additional information from readers is greatly appreciated! Australia’s climate varies considerably, and local knowledge of when particular things need to be done in the garden are most helpful to others living in those area, so please feel free to share.