Lesson 3 - Growing food plants in containers
When choosing the food plants to grow, do some planning to design your space and select your plants. Make sure you know the environmental conditions and constraints on site, the available space that you have and the types of containers you will be using. Always allow for some air movement around the containers, having them too close together can lead to disease problems later. Firstly, what containers do you have and what are their dimensions, particularly volume? Grouping your containers into different sizes - small, medium, large – can correspond to the relative sizes of plants that can be grown in these, particularly if you are planning to grow vegetables and herbs. Small plants, such as basil, chives, shallots, radishes, lettuce and spinach can be grown in containers that are as little as 1-2 litres in volume. While a more moderate container size, around 10-15 litres and at least 200 mm deep, will support a greater range of vegetables, including larger plants such as tomatoes, eggplant, beetroot, cabbage, onions and beans. Bigger containers, 20-25 litres and at least 300 mm deep, are needed for deeper rooting and larger growing plants such as potatoes, broad beans, sweetcorn, pumpkin, sweet potatoes and zucchini.
Many gardeners like to mix different plants in containers. This is a great idea as you get multiple plants in a single container but carefully choose ‘compatible’ plants in terms of their growth cycle, environmental needs and overall size. Light can become a premium when plants of varying sizes are competing in the same space meaning some plants overgrow those around them. Try to avoid the urge to overplant the container!
Diggers tip
Consider the plants you like to use and cook with. Do some research – what’s the typical growth and lifecycle for these plants? Some annual vegetables, such as radish, lettuce, kale and spring onions, can be picked a few weeks after sowing. While others, such as tomatoes, pumpkins, and garlic, will take several months.
Container growing tends to be more flexible in terms of growing compared to soil growing – the conditions are often warmer, water can be applied more effectively, and plants are more protected – enabling a wider range of plants to be grown successfully compared to a soil-grown location. This means that in some locations warm season crops can be grown more successfully in containers compared to soil growing. This is particularly true for some tropical plants, such as ginger, turmeric and pineapple, which are often better grown in containers in cooler climates. They can be moved to the best locations and bought indoors or under glass to provide protection over winter.
Another question you should ask is how much work and time do you want to put into container growing? Annual vegetables, such as lettuce, tomatoes, peas, etc. require much more input and time to sustain them when compared to perennial crops, like strawberries and chives. Some, such as rhubarb, have very low requirements and can even tolerate light shade.
Evaluate the containers that you have and the dimensions and mature sizes of the food plants that you are interested in growing. While you can prune and train plants more easily when grown in containers compared to soil, they still must ‘fit’ in the available space you have. Some plants, such as tomatoes, snow peas and cucumbers, require some form of strong physical support (stakes, frame, trellis) to fruit productively and should be placed and secured in the container prior to any planting. These supports can be up to 2 metres high with plants needing to be tied and trained to these supports as they grow upwards.
Where space is limited you might try planting dwarf or compact plant cultivars. These will be smaller than normal varieties and are more suited to container growing. Dwarf citrus varieties and many woody herbs, such as rosemary, thyme and sage, are easy to grow and can last for many years in the right container with a high-quality growing medium
Also consider the light, water and temperature needs of the plants you want to grow – do they match the conditions of your site and the resources you have? Zoning or grouping your container plants based on their tolerances and needs can help to maximise productivity.
The key tasks for container plants tend to be weeding, fertilizing and watering. Weeding is always best done before any plants set seed. Individual containers can be mulched with a 5 cm layer of organic mulch, such as pine bark or straw to reduce weeds, but make sure they are cleared of weeds first.
While many gardeners like to hand water, overwatering and underwatering tend to be major problems with container grown plants. Only water when the surface of the growing media is dry and water thoroughly. Do not water if the container is already wet and if there has been recent rainfall. Drippers or micro spray irrigation systems can also be used if you have a large container garden.
Fertilising container crops is important to securing a harvest. Remember that containers are a constrained environment and plants are only able to access nutrients in the available volume of the container. The fact that growing media in containers is more open and free draining than soil also leads to greater leaching of nutrients as the plants are growing. The addition of a pre-plant slow-release organic fertilizer to the growing media is recommended to get plants moving after establishment. This should be followed up with another fertilizer 4-6 weeks into the growth cycle as plants are growing. Further fertilizer may be needed, depending on the crop cycle. Many gardeners like to use fortnightly or monthly liquid fertilizer for their container crops. Whatever method you use, follow the fertilizer instructions carefully.
Diggers tip
When checking your containers for water, make sure there is no excess water sitting around as in some areas of Australia you are providing mosquitos with the perfect conditions for breeding.
Further learning
Further Learning
- Growing Easy Herbs for Beauty, Fragrance and Flavour by Penny Woodward (Hyland House, 2009)
- Year round greens - Gardening Australia
- How to grow onions - Gardening Australia