Jeanette is having trouble with wireworms in her potato patch and where she has grown yams.
Wireworms are larvae of Click Beetles. The larvae are shiny, brownish cylindrical creatures with 6 legs close to the head. They can grow to about 3.5 cm long, and are fond of eating roots, fleshy stems and tubers.
Wireworms can increase to pest proportions where sufficient crop rotation has not been practiced. The adults shelter in weeds or vegetable litter in and around garden beds.
To get rid of the adults, clear the garden area of weeds, old plants and mulch. You can then get the adults to shelter under a plank or bag laid on a garden bed. Early each morning, collect and destroy the beetles until it is obvious you have numbers under control.
Dig a 3 – 5 cm layer of compost into the top 15 cm of affected beds, or add plenty of organic fertiliser and grow a green manure crop to slash and dig into the topsoil when it is knee high.
Don’t grow yams, potatoes or carrots in that area again for at least four years. Rotate crops, starting with a legume, on a regular basis to prevent a build up of these pests in soil. (See Crop rotation )
Keep weeds under control and apply enough organic fertiliser to keep plants growing vigorously, and they should cease to be such a nuisance for you, Jeanette.

Other ways to grow potatoes

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.

Growing potatoes

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.

Chitting potatoes

If you can get your seed potatoes early, it will help to harden them off before planting, especially if winters are wet where you live. If tubers are kept wet soon after planting, black leg and tuber rots are more likely to occur. The hardening process for seed potatoes involves putting them in a warm well-lit area, out of direct sunlight, for a few weeks. This process is called chitting. If your seed potatoes are large, and require cutting in half before sowing, chitting is highly recommended. Don’t rub cut potatoes with wood ash, as some experts recommend. Wood ash contains a fast-acting form of calcium, and can stimulate the disease that produces “scabby” potatoes.
The segmented parts of cardboard egg cartons are perfect for chitting potatoes. Chitting also allows you to observe whether sprouts on seed potatoes are short and thick, or spindly. Seed potatoes with spindly shoots should be disposed of as they come from plants that have been infected by a virus spread by aphids. Leaves will roll upwards and plants will not produce well.

Potato beds

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.

Crop rotation

Crop rotation is the practice of allowing a minimum of three years between growing a particular family or group of plants in the same patch of soil. This practice is essential to maintaining healthy soil because it prevents the build-up in soil of pathogens that cause soil-borne plant diseases. Plants weakened by diseases also attract pests. Many modern farmers have forgotten the importance of crop rotation. The trend is towards monoculture and these farmers have to rely on stronger and stronger chemicals in an effort to cure plant pest and disease problems.
There are eight main groups of plants that are commonly grown in vegetable gardens. Some groups can be grown together but others, such as legumes and the onion family, don’t make good neighbours.
If you find that pests and disease are repeatedly affecting your vegetables, and crops are disappointing, try the crop rotation below and you will find that your garden rewards your efforts. This rotation has six sections and includes a green manure grain, plus a legume green manure if you don’t want to grow your own peas and beans. The green manures are included because they recycle nutrients, replenish organic matter in topsoil, and help inhibit soil pathogens. In this rotation, legumes precede the tomato family because broad beans inhibit a fungal wilt that affects tomatoes. Organic matter assists in keeping soil healthy because it provides a habitat for beneficial microorganisms that keep disease organisms under control and improve soil structure.
Section 1:
Legumes – peas, beans, broad beans, or a green manure legume.
Section 2:
Solanaceous – Tomato, capsicum, chilli, eggplant, pepino, potato. (Some tomato family diseases can also affect Strawberries.)
Section 3:
Crucifers – broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, horseradish, kale, kohlrabi, mizuna, mustards, radish, rocket, swede, turnip.
Section 4:
Green manure grain – such as barley, cereal rye, corn, millet, oats, sorghum, or wheat – depending on the season. Sweet corn can be grown in Section 4 if you have plenty of compost and don’t need to grow a green manure grain.
Section 5:
Chenopod family – silver beet, beetroot. (Winter spinach can follow a summer crop of beets as long as this group is not grown in the same bed for another 3 years.) Also the Aster group – lettuce, chicory, endive, globe artichoke, Jerusalem artichoke and sunflower.
Section 6:
Umbrelliferous – carrot, celery, coriander, dill, fennel, parsley, parsnip. Also the Allium family – all chives, garlic and onions.

Cucurbits – cucumber, gourd, marrow, pumpkin, rockmelon, squash, watermelon, zucchini. These, except for pumpkin, can be sown with group 5 or group 6, but not both. Pumpkins are best grown on their own because the vines are very vigorous and the roots give off compounds that can deter some other plants. Dill can also be grown with Section 3 to deter cabbage pests. Sweet corn is a good companion for cucumber or beans.

When the legumes are finished, group 2 can be planted in that bed. Group 3 replaces group 2 and so on, with all the groups moving up one bed. If you only have three or four beds, divide some of the beds proportionately, to suit your food preferences. Once your soil is restored to health, you can adjust the rotation to a three or four year one that suits the type of vegetables you prefer to grow, as long as you allow at least three years between the same group.
Crop rotation should also be practiced with flowering annuals and some perennials. Cinerarias and zinnias are related to the lettuce family, petunias are related to the tomato family, and stock and wallflower are crucifers. These plants can succumb to the same diseases that affect the vegetables in that group. Carnations and dianthus can be affected by a wilt disease if they are always planted in the same soil, and carnations, dahlias and irises can also suffer a stem rot disease if crop rotation is not practiced.