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. Temperatures may exceed 30°C in Melbourne and Adelaide.
The length of sun increases in the day, with Perth averaging 11 hours of sun a day, Adelaide averaging more than 9 hours, and other capitals more than 7 hours of sun per day.
The weather can be variable, with Melbourne’s sunny days interrupted by gusting north winds and cool cloudy weather.
Summer thunderstorms may bring wind, heavy rain and hail in some areas. Melbourne averages around 12 days of rain this month, while Adelaide averages 6 days, and Perth is much drier, seeing an average of only 4 days of rainfall for the month.
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 October (Temperate Climate)
| December Seeds to Sow and Seedlings to Plant (Temperate 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 | s | 14-28 |
| Burdock | d | 17-18 |
| Cabbage | st | 8-15 |
| Cape Gooseberry | dst | 14-16 |
| Carrot | d | 12-18 |
| Cauliflower | st | 15-22 |
| Celeriac | st | 14-28 |
| Celery | st | 17-18 |
| Chicory | st | 16-24 |
| Chinese Cabbage | st | 8-10 |
| Chives | dst | 7-11 |
| Choko | plant tubers | 17 |
| Collard Greens | dst | 8-11 |
| Coriander (Cilantro) | dst | 4-6 |
| Cowpeas (Black Eye Peas) | d | 11-14 |
| Cucumber | dst | 8-10 |
| Dill | dst | 8-12 |
| Eggplant | t | 12-15 |
| Endive | dst | 10-11 |
| Fennel (Bronze) | dst | 14-15 |
| 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 | st | 12-17 |
| Mint | dst | 8-12 |
| NZ Spinach (Warrigal Greens) | dst | 8-10 |
| Okra | t | 11-14 |
| Oregano | st | 6-8 |
| Parsley | dst | 9-19 |
| Pumpkin | t | 15-20 |
| Radish | d | 5-7 |
| Rockmelon (Cantaloupe) | t | 10-16 |
| Salsify | d | 14-21 |
| Silverbeet (Swiss Chard) | dst | 7-12 |
| Spring Onions (Bunching Onions) | st | 6-10 |
| Squash | dst | 7-8 |
| Sunflower | t | 10-11 |
| Sweet Corn | st | 11-14 |
| Sweet Potato (Kumara) | plant crowns | 15-17 |
| Tomatillo | dt | 10-14 |
| Tomato | t | 8-17 |
| Turnip | d | 6-9 |
| Watermelon | t | 9-14 |
| 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 Temperate 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.