December Seasonal Gardening Tips – Subtropical Queensland

Anne Gibson is The Micro Gardener. Each month, she shares her top tips for growing an abundance of food in our climate. Her years of experience and attention to detail make this one of the most useful guides you can get your hands on.

December

Our long, hot humid summers extend from December through March. This is the most challenging time of year to grow food and maintain a garden. Yet the heat and wet weather are also highly productive. By being prepared and with good planning, you can enjoy an abundant harvest without too much effort.

Follow my Subtropical Planting Guide for a comprehensive list of what to plant when and garden tasks throughout the year. The Vegetables Growing Guide summarises 68 of the most popular vegetables to grow in Australia and New Zealand climate zones. It includes information on companion planting, making compost, soil and moon planting. You may find these useful reference tools for growing an abundant garden.

Challenges during Summer

As the humidity and temperatures increase, pests, diseases and weeds grow in number too! Fruit flies, grasshoppers, aphids and ants, caterpillars, slugs, snails, whitefly, scale, leaf miners and citrus gall wasps, powdery mildew, sooty mould and black spot are some of the most common problems. It can be hot, dry or windy or way too wet.

Gardening can feel like an uphill battle! Preventative and maintenance strategies are needed to keep these challenges in check!

The heat also makes it uncomfortable to be outdoors. So try to get out early or late in the day during the cooler temperatures to observe, plant, water and maintain your garden.

Too much to do? Check out these helpful tips to deal with garden overwhelm and tackle tasks in small bites.

Tips to Protect your Crops

Build healthy soil. Plants that are nutrient-deficient, water or heat-stressed are most likely to come under attack. Pests and diseases target weak or damaged plants. So, remineralising your soil and providing trace elements with liquid seaweed are some easy ways to prevent attack and strengthen your plants. Check your soil pH, maintain moisture and recycle nutrients in your kitchen and garden waste to make compost. This is a sustainable way to feed your soil and grow resilient plants.

Encourage beneficial insects into your garden to pest manage for you. By sowing flowers and allowing your ornamental plants, vegetables and herbs to go to flower, you provide nectar and pollen for predatory insects like hoverflies and ladybirds who feed on aphids, scale and mealybugs. Imitate nature – you can’t go wrong! Avoid using any chemicals to attract helpful predators like praying mantids, dragonflies, assassin bugs, spiders and parasitic wasps. These insects take care of a wide variety of pests including grasshoppers, caterpillars and sapsuckers.

Use crop covers like shade cloth, a shade house, bird-safe exclusion netting, row covers and individual fruit bags to protect from flying insects, birds and other hungry animals. You may have to get creative!

Grow in containers. Move your plants under cover in hot, wet or stormy weather. Edibles in pots are portable, easier to protect and maintain, and use less water.

Easy ways to maintain a garden bed over summer

If it’s all in the ‘too hard basket’ and you need a break, consider taking some garden zones ‘out of play’ during summer. Here are a few options:

Build your soil – then set and forget. Add a layer of organic matter like aged manure, compost or garden green waste and rock minerals to a garden bed you want to reinvigorate. Mulch thickly over the top after watering in. Allow summer rain and heat to break it all down ready for planting next season. Bury food scraps and allow the worms and microbes to decompose them for you! You may even end up with some bonus self-sown crops from the food ‘waste’ with little or no work.

Grow a living ground cover like sweet potatoes or pumpkins to minimise weeds while giving you food. Sow a few sprouting sweet potatoes or plant some runners. These vine crops are thick and very effective at keeping weeds at bay while also flowering. They provide tender green shoots for salads and stir-fries, and delicious tubers and fruit.

Grow a warm season green manure to enrich the soil for planting and suppress weeds. There are many suitable seeds you can sow as a cover crop over a garden bed or larger area. Chop the crop back before flowering to add valuable minerals to the soil. Some varieties also act as a biofumigant to remediate soil infested with nematodes. You can lightly turn these into the top layer of the soil to compost or leave them in situ as a mulch. Then you’ll be ready to plant into replenished soil.

Leafy greens and homegrown salad ingredients

Just when we crave salads, many of our favourite leafy greens are challenging to grow. Quite a few lettuce varieties bolt to seed in the heat, as does annual rocket if grown in the wrong position. Swap to perennial rocket. Here are a few ideas for keeping leafy greens on your menu during summer.

Sow heat-tolerant pick ‘n’ pluck lettuce cultivars. Forget hearted varieties like iceberg – they bolt too easily! Try 'Marvel of Four Seasons', 'Freckles', 'Salad Bowl Green', 'Buttercrunch'; 'Royal Oakleaf' (my favourite), 'Green Mignonette' and 'Lollo Rossa' that are adapted for heat and humidity. Try Indian or Tree Lettuce as a hardy semi-perennial variety. In summer, I sow lettuces where they receive early morning sunlight and dappled light or under 50% shade cloth during the day. Create a suitable microclimate in a self-watering pot to prevent them bolting to seed or use a shade cover. Lettuce needs consistent water daily.

Pick young tender shoots and leaves from vegetables. New sweet potato leaves, baby beetroot and pumpkin, chard, spinach, sorrel, mustard and kale leaves are ideal to add to salads when small. Sorrel is an excellent hardy perennial.

Grow summer spinach varieties. Aibika, Brazilian Spinach, Ceylon or Malabar Spinach, Cranberry Hibiscus, Egyptian Spinach, Kangkong, Lagos Spinach, Lebanese Cress, Moringa, New Zealand Spinach or Warrigal Greens, Okinawa Spinach, Sambung Nyawa and Suranim Spinach are a few heat-loving varieties to try. Young Asian green leaves too!

Grow microgreens. These baby leaf herbs and vegetables are delicious, highly nutritious, quick to harvest from seed to feed in just 7-21 days, depending on the variety. You don’t have to worry about the heat of summer outdoors.

You can sow seeds and raise into baby leaf greens on your kitchen bench or a sunny indoor windowsill. So easy. Check out these helpful resources to get started: Microgreens Growing Guide and Easy Guide to Growing Microgreens Booklet. Simple to follow instructions, FAQ + more.

Garden Tasks

Check fruit fly traps. After rain, they become particularly active! Re-bait as necessary.
Harvest fruits and vegetables regularly in hot humid conditions before they rot or are attacked.
After rain, when soil is moist, add compost or slow-release fertiliser and rock minerals to replenish nutrients that have leached. Water in or time your fertilising before more rain and cover with mulch.
Check mulch levels on pots and garden beds. Mulch helps minimise moisture loss and weed growth, while adding nutrients to build soil health.
Install protective crop covers over garden beds. They help prevent damage from high temperatures, drying or destructive winds, heavy rain and hail during storms.
Fertilise your citrus trees. They fruit most of the year and have a high need for nutrients during summer.
Add a bird bath for your wildlife and shallow bee bath for pollinators.