Repeatedly, I come across advice to grow potatoes in a stack of car tyres. Old car tyres, when exposed to sun and rain, can leach heavy metals into soil. One of the heavy metals in car tyres is cadmium, which is known to cause cancer in humans and animals. Potatoes are very efficient at absorbing cadmium from soil, and it is not advisable to grow food crops, especially potatoes, in car tyres, or to use car tyres as compost containers.
However, if you are short of space, there are other containers suitable for growing potatoes.
Potatoes can be grown in double hessian bags, drums with plenty of drainage holes, stacked foam vegetable boxes, or wire hoops called potato cages. The newer, woven plastic feed bags may not be as efficient as the good old hessian bags, as they tend to break down quickly when exposed to sunlight. Most of these methods require one container per plant, but they allow for plenty of hilling-up and a hilled container plant will produce a larger crop than an un-hilled potato plant grown in a garden bed.
Always use a good quality potting mix for container plants, as the cheaper mixes tend to become water-repellent quite quickly, and garden soil tends to become compacted in containers. If soil is compacted, it is difficult for tubers to form. Potato plants are reasonably heavy feeders, so add a decent amount of complete organic fertiliser to the potting mix in the base of the container. Also, remember that potato plants take about 20 weeks to mature and growing mix in containers stays warmer than garden soil. Position the container where the mix won’t overheat in the warmer months.
Cultivation and hilling-up are as indicated in the “Growing potatoes” post here on Aussie Organic Gardening.
To grow potatoes in bags
Place one hessian bag inside another, and roll the sides of the bags down so that the seed potato has 15 cm of mix below and above it after sowing. As the plant grows, gradually unroll the sides as you add more potting mix.
To grow potatoes in small to medium drums
Seedlings will not receive as much light as those grown by other methods, as the seed potato is sown 20 cm from the base of the drum to allow plenty of room for hilling. Place drums in a well lit area. Ensure that the drum has plenty of drainage holes near the base. If the drum is deep, put several centimetres of gravel in the base of the drum before adding the potting mix.
To grow potatoes in foam boxes
This method requires two deep foam vegetable boxes of the same size for each plant. Make sure at least one box has plenty of drainage holes in the base. Place a sheet of wet newspaper in the base of a box with plenty of drainage holes, and cover the paper with 2 or 3 cm of gravel. Place 15 cm of potting mix in the box, sow the seed potato, and cover with another 15 cm of potting mix. Place a 60 cm stake in each corner of the box – these will hold the second box in position. Cut the bottom out of the second box. Hill the plant by placing the second box over the first, and adding more potting mix as the plant grows.
To grow potatoes in a wire cage
This method requires a 3-metre length of stiff wire mesh, about 1 metre wide. This will provide a hoop a little less than 1 metre in diameter. Wire used for concreting has holes large enough for harvesting chats through the mesh. Construct the hoop and mark the diameter on the ground. Sow 4 seed potatoes in the ground, evenly spaced within the circle, keeping them well inside the perimeter. As the plants grow, they have straw packed around them, or straw and compost, if it is available. Make sure the potatoes are well covered, or they will become green.
Gardeners in warm climates have more flexibility in when to sow potatoes. A winter crop, planted early, can mature in time to provide seed potatoes for a crop sown in a different bed, in summer. In cooler areas, where frosts can occur, early sowing can expose the plants to tuber rot, as they will be unlikely to poke their heads above soil before frosts are over. Late winter is a good time to plant potatoes in frost areas. In frost-free areas, potatoes can be sown in June or July.
Seed potatoes are sown in furrows that are 15 cm deep and 75 cm apart. Place seed potatoes 30 cm apart along the furrow, ensuring that some eyes face upwards. Rake soil over the potatoes to fill the furrow, and water gently to settle the soil. Firming soil around the potatoes can damage sprouts. The full moon phase is best for sowing potatoes and other suitable root crops.
Where winters are dry, it will help to apply mulch over the bed after sowing, as potatoes need soil that is consistently damp. Erratic watering is another cause of hollow heart in potatoes.
When plants are about 30 cm tall, start hilling them up about 10 cm at a time until the plants reach flowering stage. This will increase the number of tubers produced by each plant, as extra tubers will form from the buried stem. Potato plants should not need extra fertiliser if beds were prepared properly (see Potato beds post) but, if weather has been usually wet, an application of seaweed extract tea can be applied as plants start to be hilled.
Replace mulch after hilling to prevent any tubers produced close to the surface becoming green, and inedible. Remove flowers as they open, or the plants will divert energy into producing seed at the expense of the tubers.
When leaves start to yellow, you can harvest chats, as required, by digging carefully in the soil beside the plants. Mature potatoes for storage are best harvested during Full Moon phase, when the plants die off, and the skin cannot be removed by rubbing with a thumb. Use a gardening fork rather than a spade for digging up potatoes, and store in a dry, dark place.
Winter is the best time to plant deciduous trees, shrubs and vines, including roses and fruit trees. Evergreen plants do well if planted in spring in cool and temperate climates, or in early autumn where summers are very hot. Moon planters will plant these during Full Moon phase for best results.
• Always make planting holes wider than deep. Feeder roots are situated under the outer foliage canopy where rain drips from the plant. A wide planting hole allows the easy spread of roots as the plant grows. Wide holes are extremely important where soil is heavy. Mulch should also be applied to the outer canopy area, not near the trunk. Mulch against the trunk can cause collar rot.
• Having dug the planting hole, fill it with water and leave it for an hour or two. This practice serves two purposes. It allows you to check that the area is well drained, as few plants grow well in waterlogged soil. It also prevents water applied after planting being drawn away from the plant into surrounding drier soil. If some water remains in the bottom of the hole, plant the tree or shrub in a mound to improve drainage. If a lot of water remains in the hole, avoid planting in that spot until drainage is improved.
• Don’t plant any deeper than the tree or shrub was in the pot. Bare-rooted plants will have a change of colour on the trunk that indicates the original planting depth. This will ensure that any graft is positioned above ground level. To avoid planting deeper, lay a garden stake across the top of the hole and position the plant so that the original depth is aligned with the bottom of the stake. If necessary, make a mound of soil in the bottom of the hole to that the original planting depth can be repeated. Spread the roots of bare-rooted plants over the mound before filling.
• Fill in the hole, occasionally jiggling the trunk of bare-rooted plants to avoid air pockets around the roots, and mix some compost or worm castings through only the top 10 cm of soil. Organic matter in the bottom of the hole will cause the plant to sink as the organic matter breaks down. If you do not have compost to spare, place some well-rotted horse or cow manure on the soil surface, under the outer canopy, and cover it with 5–7 cm of organic mulch. The addition of organic matter when planting perennials is very important, as many foreign plant families (exotics), in particular, rely on a beneficial soil fungi called mycorrhiza to supply their roots with nutrients and water, and mycorrhiza live in organic matter. Without organic matter in soil, plants can struggle to absorb what they need for healthy growth, and will be more prone to pests and disease. Australian natives will benefit from the application of some leaf mould around them.
• Gently firm soil around the plant, but do not trample the soil as roots can be damaged. Water gently, to settle soil, before applying mulch. Do not apply any extra fertiliser at planting time, but an application of seaweed extract tea can help reduce transplant shock.
In temperate and cool areas, it’s time to prepare beds for potatoes, and good preparation can avoid many of the problems that may affect these vegetables. Choose a bed that is well drained and has not grown potatoes (or any of the tomato family) for at least four years to avoid the risk of several soil-borne diseases. Potatoes need a separate area for successful growth, as the plants require regular hilling for good cropping.
Potatoes need plenty of fertiliser, but don’t use fresh manures as the higher nitrogen content in these can reduce tuber production. Avoid adding lime or wood ash either, as potatoes prefer a slightly acid soil. Too much calcium in soil increases the incidence of a disease that produces “scabby” potatoes. A moderate amount of compost or well-rotted manure mixed through the topsoil is excellent. This can be supplemented with an application of poultry-based complete fertiliser or worm castings if compost or manures are in short supply. A drink of seaweed extract tea will help to satisfy potatoes’ high potassium requirement. Make sure the fertiliser is thoroughly mixed through the topsoil to avoid hollow heart occurring in tubers. After preparing the bed, cover it with several centimetres of mulch, and keep just damp until planting time.
C & D have asked do strawberries need direct sunlight in order to produce flowers – consequently, fruit? They refer to a segment on ABC’s Gardening Australia program that demonstrated a “strawberry table” where strawberries are planted directly into slashes made in a premium bag of potting medium. C & D are concerned that direct sunlight would cook all the good nutrients out of it the soil in the bag, and ask if dappled shade would be more appropriate.
The answer is this question is that a lot depends on the climate where the strawberries are grown. Some warming of the potting mix could be helpful in areas with a short growing season, such as Tasmania. Or, where strawberries are grown in winter to avoid fungal diseases encouraged by high humidity in summer. However, dappled shade would be more suitable in areas where days can be quite hot while strawberries are growing, flowering and forming fruit, in order to prevent not only cooking the mix, but also the plant roots.
In warm conditions, it is not necessary for strawberries to be in direct sunlight to form ripe fruit. If you observe how strawberries form, each flower cluster sits above the foliage. After pollination, the weight of the developing fruit pulls the cluster downwards until, quite often, the fruit is completely hidden by the foliage, and it reaches full ripeness.
In fact, as soon as our strawberry plants start forming flowers in mid spring, we place a 50% shade cloth canopy over them, positioned high enough to allow good air circulation. Otherwise, fruit not hidden by foliage becomes sunburned and inedible. The canopy also deters birds from eating the fruit. We have also had potted-up spare plants produce sweet, red fruit when grown in our shade house where they only received 50 % light through their entire growth period.
I can see a couple of problems with growing strawberries in a “table”. First, strawberry roots should be fanned out at planting, and this could be difficult to do if you have restricted access to the medium. Secondly, the bag would need holes punched along the underside to prevent the mix becoming waterlogged. Poor drainage will weaken the plants. Also, you would have to slash the bag open when runners start to form if you wanted to increase the number of plants. Strawberry plants should be replaced every two or three years.
If you would like to try this form of strawberry cultivation, avoid using a potting mix that contains a lot of mushroom compost as this is usually heavily limed and strawberries prefer a slightly acid medium. Debco make a certified-organic potting mix that would be suitable for this type of project. It is available from Bunnings stores. Unless conditions are cool, position the “table” where it gets any direct sun early in the day, rather than afternoon, and pack straw around the plants and the bag, if you feel the mix is getting too warm. However, I think growing strawberries in hanging baskets would be easier in warm conditions if lack of space were a problem – and the fruit would be safe from snails and slugs.
Over the past week, I’ve been giving both my vege patch and the some of my decorative garden a drink of seaweed tea. Seaweed extract is an excellent supplementary fertiliser. Although it doesn’t contain large amounts of most of the major elements required by plants, it contains a full range of trace elements that are essential in small quantities for healthy plant growth. I apply it when the Moon is waxing, as the increased sap flow during this period ensures quick absorption.
I often recommend seaweed extract tea to gardeners as a treatment for some plant diseases, or when pests are repeatedly attacking plants. Although it is not registered for pest control, the elements in seaweed boost a plant’s immune system and allow it to produce the pheromones that deter pests, making the plant naturally more resistant to a range of diseases and pests. Seaweed also contains a good supply of potassium to strengthen cell walls. Strong cell walls allow plants to resist the effects of drought, frost and saline soils. Seaweed compounds reduce transplant shock, and a drink of seaweed tea before transplanting seedlings, shrubs and trees will assist fast recovery. Other compounds in seaweed, called alginates, are excellent at stimulating the composting process, so the compost heap will also benefit from a drink of seaweed tea.
We use a certified-organic seaweed extract because it is guaranteed not to contain the heavy metals or industrial toxins that can contaminate seaweed collected from beaches. Acadian and Natrakelp are both reliable brands of seaweed extract. It is quite economical to use as the solution is diluted to weak black tea strength for application, hence the name seaweed tea. However, overuse of seaweed in the garden can be counter-productive. Too much potassium in soil prevents plants absorbing magnesium and calcium. But, used in moderation, seaweed is marvellous.