Grow Your Own
Page 13
Organic materials have a variable composition, and some, such as wood ash as a source of potassium, are not easy to obtain. Often this means supplementing or ‘topping up’ your solution with purchased synthetics.
That being said, it is not really difficult to grow plants hydroponically and organically at the same time. If we look at Angus’ worm ‘wee’, for example, this is very close to an ideal hydroponic feed. By steeping it with just a little poultry manure to boost the nitrogen content, an excellent balance of nutrients would result. Another terrific hydroponic feed is a nutrient solution created from quality, balanced compost. The advantage of compost and vermicast (compost made by worms) is that the nutrients have already been largely solubilised for hydroponic feeding.
Solution management
There are two methods of solution delivery used in hydroponic systems: run-to-waste and recycling. In run-to-waste, as the name suggests, the solution is passed through the system once only, with sufficient time for the plants to (hopefully) take up most of the nutrients. This method is very wasteful and causes significant water-pollution events if regulations are lax. Even with the best-balanced feed, the plants will take up what they need and leave significant quantities of nutrients in the remaining solution.
More common – and much less wasteful – is recycling, whereby the solution is passed through the hydroponic system many times, with a top-up of fertiliser at regular intervals to maintain the strength of the solution. Ultimately, however, even when using this method the solution becomes imbalanced and accumulates undesirable salts such as sodium, so it eventually needs to be ‘dumped’ and made afresh.
Hydroponic systems should always be managed so that the waste solutions and their nutrients are beneficially re-used, for example on neighbouring pasture, gardens or even tree crops. The solutions should never be discharged into dams, rivers or streams, where they will foul the water and kill aquatic life. This is one of the principal problems in countries where regulations are insufficient to prevent such irresponsible behaviour.
The nutrient solution flows around the crop roots to feed them, with the excess draining out of the end of the PVC pipes that contain the plants.
‘Soil’ for hydroponics
In practice, hydroponics uses some kind of mechanism to support the plant. This ranges from thin film – essentially a gutter that the hydroponic solution runs along; roots grow in the continuously wet bottom of the gutter – to artificial media such as Rockwool®, which is spun silica fibre. One of the most successful systems I have seen was roses for cut flowers growing in 20-litre drums brimming with 10-millimetre blue metal or rock aggregate, through which a hydroponic solution was cycled. With the high porosity and access to air, the root systems were fabulous showers of white roots disappearing into the bluish stones – a perfect combination of aeration, water and available nutrients.
Regardless of the type of ‘soil’ used, the fundamental requirement of hydroponic systems is to provide sufficient aeration to the root zone. Even short periods of stagnation and less-than-perfect aeration results in fungal-disease invasion and eventually root death. Mushy roots that are dark or black are the first indication of damping off and other root diseases.
Hydroponic production requires a large investment in equipment for nutrient mixing, so it may be beyond the scope of small urban farms.
The beauty of hydroponics is that no heavy soil is needed. Hence, these systems are lightweight enough for rooftops, patios and balconies.
Lettuce grows prolifically in trays floating on a nutrient-rich aquaponics pond that is producing fish for food.
AQUAPONICS
When raising fish is integrated with urban farming, it is known as aquaponics. This system is being used increasingly across the world, but one of the big problems with fish farming is the large amount of nutrient-polluted water that fish produce as waste. This wastewater is an ideal nutrient solution for crop growing, as one of the main reasons fish farmers have to change the water is the accumulation of nitrogen waste (urea and uric acid), which is poisonous to fish. It might be poisonous to the fish, but plants love it!
In one system we have seen, the polluted water is carried into aerated ponds that have floating Styrofoam trays planted with lettuce and other seedlings. The farmers find that little if any additional fertiliser is needed, as the polluted water full of fish excretions is sufficient to grow plants to a saleable stage. Lettuce and other fast-turnover leaf crops with a high-nitrogen requirement are their main crops.
There is no reason why the polluted water from a fish-farming set-up could not simply be used as irrigation water either in a hydroponic system – where the wastewater is run through conventional gutters – or in troughs, where the plants are grown in conventional soil or an artificial medium. Fish-farming itself is quite a skilled activity and requires plenty of knowledge and experience. Re-use of the water from fish farming would likely be far less demanding than producing the wastewater in the first place.
CASE STUDY:
THE DUTCH SOLUTION
A formula for a nutrient solution that has long been used by Dutch growers is known as the ‘Netherlands Standard Composition’, and is shown in the table below. There are many other variations, and the internet is full of recipes, both mineral and organic.
NETHERLANDS STANDARD COMPOSITION
FERTILISER SALT GRAMS PER 1000 LITRES GRAMS PER 200 LITRES
Dipotassium phosphate (K₂HPO₄) 136 27.2
Calcium nitrate (CaNO₃) 1062 212.4
Magnesium sulphate (MgSO₄.7H₂O) 492 98.4
Potassium nitrate (KNO₃) 293 58.6
Potassium sulphate (K₂SO₄) 252 50.4
Potassium hydroxide (KOH) 22.4 4.5
Chelated trace element mixture (Fe, Mn, Zn, Cu, B, Mo) 6 1.2
A standard 1000-litre container used by the food industry is ideal for making this solution, and it can be obtained second-hand quite cheaply. Another convenient vessel is a 200-litre olive drum or food-grade drum.
To make 1000 litres of solution, dissolve the dipotassium phosphate separately in about 50 litres of water, and then dissolve the other fertiliser salts all together in about 900 litres of water. When fully dissolved, slowly pour the dipotassium phosphate solution into the 900 litres of fertiliser solution while vigorously stirring the mixture. This is to prevent precipitation of calcium phosphate. To make 200 litres, simply scale down the amounts as shown in the table.
A variation on this occurs when concentrated solutions are made up. An ‘A’ tank holds the dissolved dipotassium phosphate, while a ‘B’ tank contains the rest of the nutrients. Each of these solutions is then diluted to its correct strength before the two are carefully mixed together, to avoid the calcium phosphate precipitation problem. Such systems are the most common in large commercial production.
Many green-wall systems are based on wide plastic containers like these, which can hold a lot of different plants.
Corrugated iron gutters make for an innovative vertical strawberry garden – painting them red is very eye-catching!
GREEN WALLS
In the very confined spaces of inner-city environments, sometimes walls are the only spaces available – located away from traffic and pedestrians – with the right aspect and levels of sunlight to grow plants. While the original concept for green walls was to provide an insulating and evaporative cooling system for buildings, there is no reason they could not be used for growing food.
Commercial green-wall systems can be quite costly, but with a little ingenuity they can be made by anyone with average construction skills and some common tools. In principle they use a rack system like shelves, some kind of container to hold the growing medium and some kind of irrigation/liquid-feeding system. For more detailed information on how to construct a green wall, see the step-by-step instructions within the Vertical Food Garden section.
Capitalise on your green wall
Generally, green-wall systems are best for herbs and smaller plants s
uch as chives, garnish-type crops and perennial forms of leaf crops, such as small-leaf forms of lettuce and rocket. However, smaller fruiting vegetables such as capsicums, cherry tomatoes, cape gooseberries and chillies can be planted in larger bottles.
Always have more bottles or pots on hand than are immediately needed to fill the wall, as some will be rotated to the propagating area to be replanted – and you don’t want to see gaps. Most green walls can be watered by hand, but it is best to install an irrigation system for taller green walls. This can either involve drippers to each bottle/pot, or semicircular sprayers projecting out from the wall at intervals, with the sprayers directed backwards towards the plants. An inexpensive irrigation timer saves a lot of work, and it can be adjusted according to the seasonal conditions.
Ideally, green-waste compost should form no more than 10 per cent of the growing media for edible green walls.
Growing media for green walls
Using a growing medium comprising more than about 20–30 per cent organic components is problematic for green walls, because as the components decay over time they lose volume and porosity, and therefore plant roots can’t get enough air for respiration. This has caused several expensive disasters in the early days of green-wall installations. It’s not an issue in nursery production, where turnover time is short, but it causes plenty of trouble for permanent installations.
For several large green-wall projects in Sydney and Melbourne, Simon used a mix very similar to the one in the table below.
PRODUCT PERCENTAGE BY VOLUME
Horticultural Ash 40 Per Cent
Perlite 20 per cent
Composted pine bark 10 per cent
Sand 10 per cent
Coconut coir 10 per cent
Green-waste compost 10 per cent
The mix led to excellent root development and terrific growth rates when the plants were fed using coated controlled-release fertiliser (but organic fertilisers would work just as well). The coarse ash may cause root vegetables to become deformed, but it would be a suitable addition to growing media for all other vegetables and fruits. If you replaced the horticultural ash with brick dust or fine-crushed terracotta, which is available in some places, this might overcome the problem.
CASE STUDY:
SALAD BAR
A humorous yet highly workable example of a green wall was the ‘Salad Bar’, which was created by Turf Design Studio in 2004 for the Year of the Built Environment Future Gardens exhibition. It was a 128-module system that provided 65 square metres of garden surface but occupied only 25 square metres of floor space. A quirky and amusing play on outdoor living, it is best described by the designers themselves:
The Salad Bar provides a modular vertical-growing structure with a smaller footprint to the generic garden … integrating a ‘bar’ within the vegetated wall provides a playful vision of how self-sufficiency can be incorporated into modern urban living.
The bartender can pick garnishes and make a salad without leaving the bar! The system stores and uses rainwater for irrigation. Each growing module can be removed and replanted, or it can be placed in another area (such as a greenhouse) for recovery.
CASE STUDY:
GREEN WALLS
Vertical Food Garden
Australia is home to some of the world’s most innovative horticulturists, and we would rate Mark Paul – founder of The Greenwall Company (www.greenwall.com.au) – as one of our finest. He has specialised in green walls and green roofs for over 25 years, and his design for a vertical food garden using recycled bottles provides a practical way of growing edible plants in the smallest of spaces. This design has been used in a variety of community garden projects, and has also been utilised as a wonderful educational tool in school gardens across Australia and overseas.
Mark perfected his vertical food garden concept at his nursery in northern Sydney, where he experiments with all manner of green walls, most of which are designed as low-maintenance permanent installations. His extensive experience with vertical gardening has taught him that edible plants need a much higher level of care than ornamental plants, which can cope with the variable moisture levels that most green walls experience. Mark’s long-term green walls feature plants such as succulents and bromeliads, some of which can provide an edible yield; however, this is not usually substantial enough to offer anything more than novelty value.
The popularity of growing your own food and urban farming led Mark to develop solutions to the problems of the high-maintenance requirements of edible green walls. He stresses that most edible crop plants are either too large for vertical gardens (for example, sweet corn), or demand higher levels of water and nutrients than are practical to supply in vertical installations.
Mark’s greenhouse has provided him with an environment that mimics the balcony and verandah situations that are typical for urban farmers in areas of high population density. He recommends installing a drip-irrigation system and using either controlled-release fertilisers or liquid feeding to maintain the high level of nutrition that crop plants need. Mark suggests that perennial herbs (such as mint and thyme) are more suitable for long-term plantings, and notes that fast-growing annual crops (such as lettuce) require nutritional input every day or two to reach their full potential.
Edible green-wall gardens require a considerably higher investment in time and inputs than ornamental gardens. However, in confined spaces where horizontal space is limited, the judicious use of the sort of concepts that Mark has developed can provide a viable solution.
Mark Paul attaches containers to wire mesh using cable ties.
MAKE YOUR OWN
This very simple system devised by Mark Paul is cheap, effective and very strong. Unlike commercial systems, which usually have fixed positions suitable for amenity plantings, Mark’s design works well with food-producing plants that vary greatly in size. It is made using the following materials and method.
Materials
Galvanised wire mesh, 1200 by 1800 mm, 2.5-mm wire thickness
8 x 23-mm screw hooks
Electric or cordless drill and appropriate drill bits
Masonry plugs if screwing into brick, stone or concrete
90 x 1.25- or 2-L PET bottles, washed and without caps
Porous fabric squares cut from a material such as kitchen bench wipes
2.5-mm thick galvanised wire
Metal-cutting shears or aviation snips
Pliers
Method
Line up the mesh on the wall so that the long axis is horizontal, and mark the positions of the eight screw hooks – there should be four along the top, and four along the bottom.
Fix the eight hooks to the wall by drilling (for a wooden wall) or using a masonry bit and plugs (for a brick, stone or concrete wall).
Hang the mesh on the wall using the hooks. The mesh should end up hanging just a couple of centimetres off the wall.
Cut the bottom off each PET bottle at an angle so that the bottle ends up being about 200 millimetres in length on the long side. Then make a 3-millimetre hole in the long side.
Turn one bottle upside down, plug up the hole in the neck of the bottle with fabric squares, and fill the bottle with growing medium to the top of the short side.
Make a small S hook with the galvanised wire, and use this to suspend the bottle in whatever position you want. Repeat the process for the remaining bottles. A 1200- by 1800-millimetre piece of mesh should hold around 90 bottles.
You can make as many of these units as you like, joining them together to create larger green walls. In addition, you can use small plastic pots instead of bottles. The little pots will lean forwards a little, which looks very appealing once they are filled with lush plants. This simple system has the advantage of allowing you to move plants around at will, depending on their size, so you can close up the spacing between smaller plants or open up the spacing between larger plants – consequently, you can maintain the overall green appearance of the wall very easily. You can al
so change pot sizes as required, provided that weight does not become an issue for the larger pots.
Clockwise, From Left: this recycled PET bottle has various holes so that it can be hung on the wire mesh, and for drainage and aeration; porous material is used to prevent the potting mix from falling out of the drainage hole; a lightweight, freely draining, 50:50 blend of perlite and coconut coir is an ideal potting mix for this green-wall system; plant your choice of seedling herbs or salad greens in the PET bottle, and hang the bottle on the wire mesh.
Greenhouses or conservatories are best constructed beside eastern- or northern-facing walls in Australia.
PROTECTED ENVIRONMENTS
Greenhouses, glasshouses and poly-tunnels are used to extend the growing season of warm-season crops, hence they are most beneficial for gardens located in cool climates. They are often used for the growing of tomatoes and cucumbers in the ‘off-season’, or the winter months. Market prices are better in the off-season, which justifies the added cost (if you plan to sell your produce), or you can use the structures to ensure you have vegetables on the table year-round (if you are harvesting for your own use).
The most common form utilised these days is the relatively low-cost poly-tunnel. A semicircular metal structure is placed over natural soil (which has been hilled up to improve drainage) or a raised bed, and then covered with a horticultural-grade plastic that has been manufactured to better withstand ultraviolet radiation from the sun. Small kits can be purchased fairly cheaply, and there are also systems available that are made from partly rigid plastic agricultural pipe bent into a series of semicircles, like ribs. The pipes are then joined together with wire to form a self-supporting structure, before being covered with plastic film. This is an affordable and very effective approach.
Pros and cons