There are two sorts of strawberries. The most popular have large, succulent fruit and come in various shades of red. Almost invariably, they are propagated vegetatively, by planting runners. The plants make shoots, which terminate in a miniature plant that, given the opportunity, will form roots and grow into a full size strawberry plant. The other sort is generally grown from seed. These are variously known as alpine, or ever bearing. The fruits are much smaller and the crops are lighter. The berries of some strains of this species are white, or cream, as well as the various shades of red. Many have a more intense flavour than the common strawberries, but the yield is very low. To make up for this, they set fruit over a much longer period.
Strawberries are very easy to grow, provided their requirement for copious quantities of food and good drainage are met. As they can have a long and productive life, two to five years, it is important to plant them in weed-free soil. Mulching is generally used to keep the beds that way. The most common mulch is black plastic, but this material, apart from being an ecological disaster, removes the benefit of rainfall. Irrigation is the trickle sort underneath. Also, the plastic reduces gas exchange between soil and the air, to the detriment of root health. Organic mulches are to be preferred. The most common is pine needles, as strawberries are said to like the acid conditions this creates. Certainly, strawberries tolerate acid conditions well. Straw, seed-free hay and compost make excellent mulches.
When a lot of strawberries are grown, they are planted in raised beds 15-20 cm high and 120 cm wide with 45 cm wide footpaths. The strawberries are planted 30 cm apart in a double row. With 132 plants per 10 m of bed space, 1,000 square metres (a quarter of an acre) will accommodate about 6,600 plants. These could yield 7 tonnes, or more, of fruit.
In cool and mild climates, planting is mostly from late autumn to mid winter.; in warmer climes, earlier planting ensures a good winter crop. Summer planting of cool stored plants is often practised. These plants crop within a couple of months and the following spring, out produce those planted in autumn. Planting in summer requires trimming the leaves, to reduce the stress of transpiration, and they must be kept well watered.
Water requirement is estimated to be 4.5 litres per plant per week at an evapo-transpiration rate of 25 mm per week. This would double in hot weather. Trickle systems are the most commonly used to deliver the water needs of strawberries, but overhead irrigation is probably better in hotter conditions, as the water helps cool the plants.
Runners must be removed throughout the growing season to keep the plants' energy for fruiting. Runners used for propagation are generally taken from young, non-fruiting plants. Plants for reproduction are grown where there is no danger of infestation by the strawberry aphid, which carries virus diseases. It is build-up of these diseases that necessitate the introduction of new, virus-free plants every two years or so. Under organic conditions, the build up of virus appears to be much slower than where conventional methods are used.
Removing the leaves immediately after the summer crop can stimulate the plants to grow a second crop in the autumn. Some growers remove the first flowers in the second year of fruiting in order to encourage more vigorous growth and a higher, though later, yield.
The fruit is picked by severing the stalk between finger and thumb. The fruit is easily bruised and should be handled as little as possible. The time to pick is as soon as the fruit is fully coloured. In hot weather, daily picking will be necessary.
There are different varieties for different climatic regions. Plants can be obtained from your local nursery, or purchased by mail order.
Cambridge Vigour is an early variety and difficult to obtain these days. The fruit has wonderful flavour and the plants can be forced to grow an autumn crop. It crops too lightly to be considered a commercial variety. This variety suits cool districts.
Red Gauntlet is the main commercial variety because of its high yields and extended fruiting season. However, it has almost no flavour and on that count is probably not worth growing.
Rabunda is said to produce a light coloured, soft fruit with a flavour resembling wild strawberries. Unfortunately, I cannot comment on this, as here in Southern Tasmania, my plants failed to flower or set fruit. Perhaps they do better in warmer conditions.
Shasta is a warm climate, mid-season variety and is reputed to have good flavour.
Tioga has an extended fruiting season and the berries are the best tasting of the commercial varieties. The fruit is large and the colour excellent.
Totem has a small, dark red berry and is said to have a very aromatic flavour. Its yield is low.
Sweetheart is grown from seed, crops well though it has nothing startling to recommend it above Tioga. The seed needs cool conditions to germinate satisfactorily.
The alpine, or ever bearing strawberries are all grown from seed. The seed is sown in autumn or spring in cool, damp soil. The seedlings are pricked out and planted where they are to grow. Generally, they are grown as annuals, though they are perennial. They are grown somewhat closer than conventional strawberries, about 20 cm apart. They bear earlier than their cousins and crop continually through until autumn. The yields are too low to consider them as a commercial venture, unless a restaurant can be found willing to recompense the grower satisfactorily.
Strawberry aphids are the main insect pests of strawberries and are found under the leaves, which they distort, and they transmit a variety of viral diseases. Reflective foil under the plants is said to repel them, and soft soap solution, or pyrethrum will kill them. Compost fed plants are less attractive to them than those grown with water soluble fertilisers. The most serious pests of strawberries are snails and birds. Netting keeps the birds at bay and regular removal of snails will keep them under control. Nets must be secure at the edges where they touch the ground; the determination of birds to eat the fruit is great.
There are several fungal diseases of strawberries. Grey mould (Botrytis) is the most common and destructive. It rots the blossoms and fruit in humid weather. It is probably worth trying regular sprays of 3% waterglass (sodium silicate) solution in these conditions. Verticillium, Fusarium and nematodes are all soil borne organisms that should not be a problem if strawberries are not grown in the same ground for too long.