Growing food

Wicking beds are a type of enclosed container system that has a reservoir of water at the base that supplies plants with constant moisture. The water is drawn upward through the growing media by capillary action (‘wicking’) to the root zone where plants can then access it. Apart from initial planting and rainfall there is no watering of the bed from the surface. Wicking bed systems are built in layers and need to be constructed carefully to make them successful. The basal reservoir typically includes large-sized gravel to support the growing media above and store water at the same time. Above this layer is a permeable fabric or geotextile that allows water to move upwards through capillary movement but stops any growing media from entering the reservoir section. Then there is the growing media layer, which is perhaps the most critical. It needs to be a high-quality media to ensure that water draws upwards into the rootzone through capillary movement. The growing media will always be moist, at least just below the surface, ensuring that plants always have a constant source of water. 

While there are costs associated with the initial set-up of a wicking bed, there are many advantages for the home grower. They use significantly less water that overhead watering or irrigation systems, which is particularly useful in areas where water may be limited. Also, plants are supplied with a consistent water supply, matched to their stage of growth, which can result in more uniform and healthier produce. However, they are not as portable as smaller containers, weighing up to 400 kg when full, so their placement needs to be considered carefully. Many gardeners have constructed their own wicking beds from old baths or similar structures, examples can be seen online. There are also commercial systems that home gardeners can purchase, such as Biofilta Foodcubes and Waterups.

Hydroponics is a method of growing plants in the absence of soil. There are different growing systems for hydroponics, but they all rely on having a water-based solution that provides plants with the nutrients, water and oxygen for them to grow successfully. Most are systems where plants are grown in a controlled environment, such as a greenhouse or shadehouse, with plants mounted on a supporting frame or trellis. Their roots are submerged in an aqueous solution or are grown in an inert substrate, such as coir (coconut fibre) or perlite supplied with a nutrient solution. This solution contains all the essential elements for plants to thrive and is reticulated and oxygenated to support healthy root growth. Many vegetables and fruits are grown in commercial hydroponic systems, but there are also increasing numbers of home growers using hydroponics. Plants tend to grow more rapidly, with higher yields and improved quality of produce being the main benefits. There are initial costs in setting up hydroponics and it certainly helps to have an interest in plant nutrients and growing methods to ensure you can maintain the system successfully. But the efficiency and productivity of small hydroponic systems makes them very attractive to some home growers.

One of the more interesting applications for hydroponic food growing has been in living walls. Living walls are where plants grow vertically on a structure, supported in small containers fixed to the surface of the wall, or in fabric or felt pockets fixed to the wall and filled with a small amount of inert growing media. Most are hydroponic systems with a reticulating nutrient solution that ‘feeds’ and supplies water to the plants as they grow. Living walls systems can grow a variety of shallow-rooted vegetables, particularly plants like salad greens and strawberries. There are good examples online of both ‘home-made’ living walls and smaller commercial systems suitable for the home gardener. The initial outlay for installation of a living wall can be significant and it can take a little time to understand their operations and management, particularly the reticulated nutrient solution. However, increasing numbers of people are installing productive living walls as they can be an excellent way to growing food in small spaces.

Another alternative way of growing food in a ‘container’ is through a green roof. A green roof is a way of growing plants directly on the roof or terrace of a building and consists of a series of layers that protect the roof structure and support the vegetation growing above it. These layers include waterproofing directly on the roof surface, followed by a drainage layer that drains water off the roof, a fabric or membrane to maintain integrity of the drainage, a growing medium or soil layer, and finally the plant or vegetation layer. Green roofs range from being very shallow (10-15 cm deep) and low maintenance installations (extensive green roofs); through to deep ‘roof gardens’ (100-200 cm) that have diverse vegetation and high maintenance (intensive green roofs). 

It's possible to grow a range of vegetables and some fruiting plants on roofs, but there are some aspects to consider. Perhaps the easiest to install are small flat containers or examples such as wicking beds, that can be placed directly on the roof structure. Alternatively, you can purchase a green roof system that can be designed to fit your situation and site. Ideally your site is not too windy or too shaded, as these conditions can affect the growth and productivity of any your plants. Weight-loading, access, drainage, irrigation and maintenance are the main issues to consider. The overall weight of the green roof system must be matched with the structural integrity of the roof and generally requires advice from a structural engineer. Most of the mass is in the soil layer of soil, so the deeper this is, the heavier the green roof will be. Most vegetables require at least 25 cm of soil depth to grow, while woody plants like shrubs and trees will need two or three times this depth. Safe access to the roof is important, both to maintain the plants, but also for topping up the growing media each year. Good drainage is essential for a productive green roof, as is irrigation, with drippers or micro systems the most efficient to use. And like any garden, green roofs require maintenance, particularly pests, diseases and weeds, although these problems tend not to be as significant as they are at ground level. Shallow-rooted vegetables and fruiting plants are those best suited to green roof growing, such as salad greens, brassicas, beans, herbs and strawberries. The conditions of higher light and elevated temperatures, compared to ground level, can be beneficial if you are growing longer-season crops, such as melons, but it also requires vigilance around irrigation as plants will have a higher water demand over summer. There are some wonderful examples of productive food growing on green roofs including these two in New York – Brooklyn grange and Eagle street.