A Short Guide to Strawberry Growing

Transcription

1 Introduction Strawberries (Fragaria spp.) are hardy herbaceous perennials, though it is rare for all leaves to die off completely, except in the harshest of winters. They prefer a rich deeply dug well-drained soil, that doesn t become waterlogged, nor dries out too quickly. Well-rotted farmyard manure or garden compost may be incorporated into the soil initially, to aid the soil structure. Poultry manure should never be used. Strawberries require a site with an open sunny aspect, which is sheltered from winds, relatively free from late frosts and not in a frost pocket. Ideally the soil should have a ph of around 6.5, but as low as 5.5 and as high as 7.0 can be tolerated. There are two main groups of strawberry, the single crop group and the ever bearing or perpetual fruiting group. The single crop group is further classified into early, mid, and late summer varieties. They bear their fruit over a period of 3-4 weeks during the months of June, July, and very early August, depending upon variety. There may be some overlap between cropping of different classes depending on variety and weather. The everbearing varieties bear a small flush of berries in early June, then have a break in fruiting until August, when they will flower and fruit continuously from then until late October, but by this late date there is usually insufficient warmth for ripening. To maximise the yield of the later crop on the ever bearing varieties, it is preferable to remove the flowers of the early spring flush in May. Planting of new runner plants can be carried out in late autumn to late winter/early spring, providing the soil and weather conditions permit. Do not plant strawberries where potatoes have been cultivated during the previous 5 years, as this can infect the runner plants with a serious disease, Verticillium wilt. The soil should be as free of annual weeds as possible, and no persistent perennial weeds should be present. Regular weeding should be carried out throughout the year, as the crop yield of strawberries is adversely affected by competition from weeds. Weed suppression by planting through a plastic mulch of black polythene can be used but irrigation under the mulch will be needed. Laying a seep hose on either side of the intended planting row, before laying down and securing the polythene, will be necessary. Alternatively, a porous weed suppressing membrane may be used, which allows water to percolate downwards, without allowing weeds to grow upwards. Commercial growers will use pre-emergent herbicides, though these will reduce the vigour of the plant to a slight degree. If using a membrane it may be useful to scatter some slug pellets underneath before laying, or alternatively apply a layer of coarse sharp grit beforehand. Newly received bare-rooted runner plants, lifted and delivered between October and early April, can be kept moist, prior to planting, by wrapping the roots in wet newspaper, and storing in a cool frost free 1

2 place for up to a week. Cold-stored runner plants, obtained between late April and July should be planted within 24 hours of receipt and thoroughly watered in. Runner plants may be planted on the flat, or if the ground is on the heavy side can be planted on ridges raised up to a height of between 4-6 inches ( mm) to assist drainage. Rows should ideally be 36 inches (900 mm) apart, though not less than 24 inches (600 mm) may be used if space is tight. Plants within rows should be between inches ( mm) apart. It is important to ensure that the crown of the plant is level with the soil level, as planting too deeply may cause the crown to rot, and planting too shallowly will leave the roots exposed. Nitrogenous fertilisers should not be used on strawberries as a rule, though a light base dressing immediately prior to planting may be given to help the establishment of the plants. Also another light top-dressing may be given to promote new growth after the leaves have been stripped after harvest. It may also be desirable to give another top-dressing if the plants have suffered a loss of vigour in the last year, or so, of their cropping life of 3-5 years. In every case the application of nitrogenous fertiliser should be treated as an exception to the rule and only given as a matter of necessity. Too much nitrogenous fertiliser will cause rank leafy growth that will adversely affect the production of flowers and the eventual yield of the fruit. A base dressing of phosphate and potash based fertilisers should be given prior to planting, followed by an annual top-dressing in early spring of each succeeding year. Superphosphate of Lime and Sulphate of Potash are the usual choice, applying 15 gm and 35 gm respectively per square metre. For those wishing to avoid synthetic fertilisers, rock phosphate, and Vitax Organic Grower High K (Soil Association approved), or other potash-rich organic fertilisers, may be substituted. Do not apply more than the recommended quantities in the expectation of an extra bumper crop. It will do more harm than good. The following timetable is given as a guide to the strawberry year, though exact timings may vary according to the weather and varieties grown. February Apply top-dressing of phosphate and potash fertilisers. Firm in any crowns that have been lifted by frost. Hoe lightly to remove any weed seedlings, taking care not to disturb the roots or crowns of the strawberry plant. Dig out any perennial weeds that are showing, or treat individually with glyphosate weed killer (Round Up). Avoid splashing any strawberry plants with this weed killer. Repeat as necessary through the year. When using herbicides, read and observe the instructions on the label. March New leaf growth will commence as the weather warms up. Aphids may attack the new leaves, spray with Bifenthrin based insecticide, or alternatively, use soap based organic spray. Keep any emerging weed seedlings down by hoeing or hand weeding. When using pesticides, read and observe the instructions on the label. April Further new leaf growth and threat of aphids, continue with insecticide sprays. Continue with hoeing and/or hand weeding. Do not irrigate unless it is absolutely necessary. Excess water at this stage will promote leafy growth at the expense of flowers. Watch out for signs of powdery mildew on the leaves, especially during a dry spell. Treat with myclobutanil (Bio Systhane), or a permitted organic copper-based fungicide. Repeat at fortnightly intervals, but allow at least 14 days from the last spray before fruit picking. This is the harvest interval. When using fungicides, read and observe the instructions on the label. May It is often recommended not to allow newly planted runners to bear fruit in the first year. Providing the new plants were planted early enough, are established and growing vigorously, they can be allowed to bear fruit in their first year. Most amateur growers can t resist the desire to taste their new crop anyway! Only if the new plants lack vigour is it advisable to forego the initial crop and concentrate on establishing them. Once flowering has commenced, and fruit begun to set, ensure that the crop has adequate water. Do not allow the crop to become dry, so ensure there is enough, but not too much, water, to swell the developing fruit. Continue to spray against aphids and powdery mildew. Protect 2

3 flowers against late frosts by temporarily covering with fleece if threatened. Remove fleece immediately threat of frost has passed. Do not leave the fleece in position as this may prevent adequate pollination by insects. If frost damages the flowers it will turn the central disc of anthers from yellow to black, unsurprisingly this condition is called black eye. These flowers will not develop into fruit, but die and rot, increasing the risk of fungal infection by grey mould (Botrytis). So pick them off the plant as they are found. Continue with weeding and protect against slugs, by using slug bait, either metaldehyde based, or organically by using ferric phosphate based pellets ( Ferramol ). As the fruit begins to swell, and danger of frosts has passed, commence strawing down by packing fresh dry straw (Barley straw preferably, if obtainable) around the plants and supporting the shoots of developing fruits. Do not straw down before this stage has been reached, as it may increase the risk of frost damage. Pick off any damaged or diseased fruit or leaves as they occur. Spray against grey mould (Botrytis cinerea) and powdery mildew, bearing in mind the need to leave at least 14 days between the last spray and fruit harvesting. If birds are a problem in the area, erect a light structure to support some netting to cover the crop. Ensure it is completely bird-proof, and erect it before the fruit begins to ripen, birds will sometimes go for green fruit. June Depending upon variety, fruits will continue to swell and ripen during this month and the next. The cropping period will usually last for around three weeks. Continue to ensure that the plants have adequate water, but try to water the soil rather than the plant. Remove any fruits or leaves infected with grey mould immediately they are spotted. Pick ripe fruit early in the day when any dew has lifted and the crop is dry. If picking later in the day, keep harvested strawberries out of the sun and somewhere cool. Try and spread them out on a tray in a cool breezy shady place to remove the field heat as quickly as possible. Field heat is the warmth the fruit has absorbed during the day in the sunshine. It causes the fruit to respire and transpire freely which needs moisture uptake from the plant. When picked, the fruit will continue to lose water, but as the connection with the plant has been severed, the moisture cannot be replenished and the fruit will dehydrate, badly affecting its keeping qualities. Cooling the fruit rapidly slows down respiration and transpiration, so it loses less moisture and keeps better. Do not delay in placing the fruit in a refrigerator as soon as the crop is taken home. Unless, of course, it is to be eaten immediately! When picking fruit do not handle it directly with the fingers. Instead pinch the stalk between thumb and forefinger, whilst allowing the fruit to rest gently on the palm of the cupped hand. Leave the stalk and the green calyx attached until ready to use the fruit. If the ripe strawberry is grasped with the fingers it will bruise the delicate skin, which will rapidly develop into a slimy fingerprint and mar the fruit. As the crop begins to ripen the strawberry plant will also start to throw out runners. Continue with weeding as necessary. July Continue with harvesting as the strawberries ripen. Ensure adequate moisture is present. If plastic mulch has been used instead of straw, ensure that it does not become so hot that it cooks the strawberries. It may be necessary to lift the fruit off the plastic mulch and support it with a handful of straw. Continue to remove any infected fruit and leaves. Continue weeding. The runners will continue to grow. If new plants are required elsewhere, then the runners may be allowed to root in pots of soil sunk alongside the row. As soon as the harvest is over, after the last berry has been picked, clip off all the leaves and stalks from the plant with no more than a weeks delay. It is important not to putoff this operation. Remove the straw also, so that it doesn t harbour pests. At one time the straw was fluffed up and set on fire. This not only got rid of the straw, but any pests also, but it is unlikely to be considered acceptable nowadays. Do not delay in removing the old leaves. If an increased number of plants in each row is desired, rake the runners back into the row and allow the required number to take root, or to re-root. This will still leave the pathway between the rows clear, and give free access for weeding and harvesting in subsequent years. Do this in the first year only; in successive years remove all the runners as well as all the leaves. This creates what is called a matted row, containing plants a year apart in age. Providing it is not too crowded with new plants, the row will continue to thrive and give an increased yield in successive years. This cannot be done if plastic mulch has been used, as the runners cannot root through the plastic. Leave any potted runners until the autumn. Clean and tidy the plot of weeds and leaf debris to minimise the harbouring of pests or disease. 3

4 August The single crop plants will have finished or shortly come to an end. See the notes about leaf removal and runner treatment in the July section. These plants will now be sending up new fresh leaf growth, and adequate water should be given to encourage this. If the plants lack vigour a very light top-dressing of a nitrogenous fertiliser may be given. Do not be tempted to give a heavy dressing as this will lead to lush sappy growth, which will be badly affected by the cold weather over winter. If in doubt, leave it out. If perpetual-fruiting or ever bearing strawberries are being grown, and they were disbudded in May, they will have recommenced flowering in July and start to ripen their fruit in this month. At the same time they will continue to flower and set fruit until the first frosts in October, though lower temperatures may prevent late ripening. Additionally they will send out runners that will root and flower and set fruit almost immediately to add to the crop yield. Although the crop will not ripen as a flush within a period of three weeks like the single crop type, overall the total yield will be broadly similar, just spread out over a longer period. Do not remove the leaves, or the runners, though runners can be rooted in pots if extra plants are required. September With the onset of shorter days from the 21st onwards, the new fresh leaves that have grown on the one-crop varieties will be building up food reserves and new embryo flower initials will start to be produced in the crowns for next year. The leaves detect the change (shortening) in day length, and this triggers a hormonal response in the plant to commence flower initial production. The embryo flowers will not be apparent externally, as they are hidden within the tissue of the crown. The old leaves are senescent and incapable of producing sufficient food reserves. Additionally they will be using food reserves produced by the new leaves to help them linger on, rather than allow a build up in the crown for the following year. They are also less sensitive to changes in day length and slow down the initiation of flower embryo development, resulting in a reduction in flowers, and fruit, in the following year. This is why it is important to remove the old leaves immediately harvest is over. The development of flower initials will reach a peak during October and early November and the plants must be allowed to mature without competition from weeds during this period. October, November, December, January The strawberry plants will become dormant as the year draws to a close, the single-crop varieties first, followed by the perpetual-fruiting varieties, but it is still necessary to continue weed removal. If the pathways between rows have become trampled and compacted, and waterlogged during the summer and autumn, a light forking to loosen the soil will improve drainage. Keep crowns firmed in, if lifted by frost. Any straw, or leaf debris should have been completely removed, including round the perpetual varieties. But do not remove the leaves, or runners, of perpetual varieties until late January or early February when the cycle of the strawberry year begins again. During this period, strawberry bed renewal or extension may take place on freshly prepared ground. Do not replant strawberries immediately where strawberries once were, leave at least five years before reusing the ground, and do not plant where potatoes have been grown during the previous five years. If you have space, create a new row of strawberries each year, after the first year, so that as the yield of strawberries declines in the older plants after the third or fourth year, the younger plants will fill in the slack. Do not keep your strawberry plants beyond their useful life of between 3-5 years. Be ruthless, once the crop begins to decline, root out the old plants and dispose of them. If you are tempted to keep them for too long there will be an increased risk of a build up of soil-borne disease, which could infect the whole area and prevent the growing of strawberries for long into the future. The alternative then would be to find a completely new site or resort to growing in grow-bags. Many amateur growers propagate their own plants, or accept spare runner plants from friends or neighbours. It is important that only healthy stock is propagated, and it is worthwhile asking to inspect the stock through the preceding growing season before accepting plants from others. If in any doubt that the plants are healthy and free from disease it is better to politely decline, rather than import trouble. Though certified stock plants cost more than the freebies, their use will ensure that your fruit growing gets off to the best possible start with less likelihood of disease inoculation at the outset. 4

5 Varieties of Strawberries A Short Guide to Strawberry Growing Early midsummer Mid midsummer Late midsummer Perpetual fruiting Honeoye Royal Sovereign Cambridge Vigour Gorella Mae Gariguette Cambridge Favourite Pegasus Elsanta Red Gauntlet Cambridge Late Pine Hapil Florence Rhapsody Laura Maxim Flamenco Calypso Aromel Ostara Comments Honeoye is an American variety, good yields of large fruit, has become popular for the early market. Gariguette is a French variety, first introduced in the 1930's. It is considered to be one of the finest flavoured varieties (especially by the French). It bruises easily, and does not travel well, so is little grown in this country commercially, though it may be found in up-market stores, like Harrods & Fortnums. It has oval (egg-shaped) fruit, unlike the traditional conical shape, and needs good growing conditions to thrive. Cambridge Late Pine is considered to be the English equivalent of Gariguette in terms of flavour, even though later maturing, moderately good yields. Elsanta is a Dutch bred variety, that has gained the lion's share of the main commercial growing market as it is bruise resistant and can withstand the rigours of distribution, though there are other betterflavoured varieties. Florence is a modern late variety with good yields and flavour Maxim produces fewer but 'whopping-big' fruits, so if size matters more than flavour, try this. Flamenco is a great new introduction to the perpetual fruiting varieties, with good yields and flavour. 5