Strawberry production has advanced in leaps and bounds over the past 10 years. Gone are the days when summer picking lasted just five or six weeks followed by a short everbearer season with varieties that were poor quality by today's standards.
Now growers have extended the picking season to 10 months or more thanks to the use of eight different types of planting material and protection including glasshouses and polytunnels. With the help of heating and night-break lighting, the first glasshouse crops are picked in March, although without these inputs the harvest generally begins in southern England in April.
Glasshouse production is only a small proportion of the total, however. By far the largest volume of fruit comes from polytunnels, the earliest being picked in late April to early May in closed structures. Then, around mid-May in the south, cropping in French and Spanish tunnels begins, brought further forward with fleece or polythene covers. It continues until October, the main season being extended into July and August with 60-day crops that overlap with the first everbearers. In addition, traditionally-grown unprotected crops are picked in the main season through June and into July.
To achieve the continuity of production over such a long period entails a good deal of skill, knowhow and planning. This is made clear in an Horticultural Development Company (HDC) factsheet "Extending the UK strawberry season using a range of plant types and growing systems", to which HDC's communications manager Scott Raffle, ADAS's Robert Irving and Farm Advisory Services Team's (FAST) Graham Moore contributed.
Improvements in growing systems have been accompanied by increased and more consistent fruit yields and quality. For example, when 60-day production was being developed in the 1990s, yields averaged 5 tonnes/ha. They have since increased up to threefold to as much as 25-30t/ha. That applies particularly to the higher-value plants such as tray and waiting-bed plants.
Strawberries are a high-input, high-output crop with picking costs for bed-grown crops accounting for 20-30 per cent of total variable costs. Lower-yielding crops of 18-23t/ha are more expensive to pick, at £13,000 to £17,000/ha according to John Nix's Farm Management Pocketbook. In contrast, crops of 20-30t/ha cost £11,000 to £19,000 to pick, accounting for 22-25 per cent of variable costs.
However, variety can make a big difference to picking costs/hour. Because breeders select for high yield and large, well-presented berries, the latest varieties tend to be less expensive to pick. Growers continue to strive for lower picking costs, though. Many have invested in tabletop systems in recent years and some in picking rigs for bed-grown crops.
Peat-based module substrates remain the widest used but the most popular alternative is coir, claims West Midlands soft fruit adviser Chris Creed. Coir's biggest potential benefit is that it is sustainable, "although in the long term it's probably not". It also holds plenty of air, whereas peat does not unless it is quite coarse, and is less prone to slumping.
Producing high strawberry yields ultimately comes down to growers paying attention to detail. That applies particularly to crop establishment, because plants that grow away well without a check are very likely to be the most productive.
This is made clear in the HDC factsheet, which stresses that failure to ensure good plant establishment leads to poor growth, more disease and reduced yield in the year of planting and subsequently. Plants must arrive in the field in which they are to be planted in the best possible condition. That means taking good care of them at each stage of the operation.
The factsheet also points out that the planting medium, soil in the case of raised, polythene-mulched beds and the module substrate for tabletops, must also be of a high standard. Ideally beds should be prepared in the early autumn for autumn or spring planting while it is still easily worked and before adverse weather sets in to make travelling conditions difficult. For the best sterilisation results the soil should be warm, moist and friable. The polythene mulch preserves the bed's tilth through the winter.
Several steel tools are used for planting. The main type for bare root plants is a T-bar with a two-pronged fork at its business end. The fork is placed about two-thirds down the length of the roots and pushed into the soil in the planting position taking the rest of the root mass with it so that the plant's crown is flush with the soil (or substrate) surface. When the roots are at the required depth the tool is withdrawn and the soil firmed around the crown.
For pot-grown or module plants, such as tray plants, a standard trowel is used for planting. It is inserted in the soil or substrate to full pot or module depth and pulled backwards to create a space into which the plant is placed, again to crown level. The medium is then firmed around the plant's roots.
The factsheet states that when planted in the spring or summer the plants are usually misted until first open flower to minimise evaporation and transpiration. In addition, overhead irrigation can be used to help settle loose soil around the roots.
Of the eight plant types, the most widely used are autumn and winter-lifted runners. These are graded into three crown sizes - A+15mm or more, premium 12-15mm and 12mm or less - and cold stored (at -1.6 degsC) until required.
After planting the usual procedure is to take a 60-day crop in the first year and a main crop in the second. Bed-grown plants are then ploughed in but to reduce costs some growers pull the old plants out and plant new ones in the same holes. This works well provided the old plants are healthy. With tabletops, replanting is common practice that tends to work better with coir modules because they slump less than peat-based ones.
"Tabletops will definitely continue to increase because their picking costs are about 20 per cent lower than for raised beds," maintains FAST's soft fruit specialist John Handford. "But it's not just the ease of picking. They make picking a more attractive job, which is important because labour is getting more difficult to obtain and keep happy."
Handford estimates that of the growers he visits in England and Scotland, 20 to 30 per cent have switched to tabletops. Richard Brown of Hortech Solutions, a tabletop structure supplier, reckons the figure is nearer 30 to 40 per cent, while Chris Creed puts is at only 10 to 12 per cent in his area.
These figures seem certain to increase because of tabletops' numerous benefits. The need for soil sterilisation is eliminated and vine weevils are better controlled with nematodes in the substrate of tabletop modules. In addition, the polytunnels housing the system can be permanently placed on the most favourable site near the packhouse, cold stores and fertigation equipment, rather than the tunnels being moved around.
However, tabletops have one major drawback: the high cost of their support structure of £5 to £8/m or an average of £40,000/ha, assuming a row length of 6,200m/ha. The outlay on modules is generally £1.30/m or £8,000/ha. Although modules need regular replacement, most growers get two to four crops out of them.
There also have at least one agronomic drawback: it is harder to produce early crops of June bearers. On the other hand, Brown maintains that their crops can be manipulated better than soil-grown ones and says yields are higher. He always assumes a yield of 25 to 27t/ha for raised beds and 30 to 32t/ha for tabletops.
"A big reason why my growers are doing more tables is that they no longer have the clean ground to produce strawberries," he declares. "It's easier to put in tabletops than finding clean ground miles away and installing a reservoir or borehole on it."