Greenhouse tomatoes
While most tomato crops are field grown, glasshouse or plastic tunnel production is increasingly important for the supply of fresh fruit to local markets.
Unlike shorter season field crops, a greenhouse tomato crop can be maintained for up to 11 months. Greenhouse crops are generally harvested green and ripened during transport and on the supermarket shelf.
Vine ripened fruit from glasshouses tend to have a longer shelf life, a better flavor and a higher market value than those grown in soil outdoors. Plants are trained – normally up one single wire – with suckers removed to maintain a single stem. Once the first clusters have been harvested, the crop can be progressively lowered to maintain the crop within easy reach. Fruit, or flower clusters are trimmed to an acceptable length, number and fruit weight for the market.
High levels (600 to 1000ppm) of carbon dioxide are maintained in the greenhouse atmosphere to increase photosynthesis, growth rate and crop yield. Such a practice is often employed in lower yielding regions and under more intensive production systems. Most intensive greenhouse crops are now grown in substrates – e.g. rockwool or perlite, though soil-grown tomatoes are still common under tunnels. Fertigation ensures accurate nutrition eliminating many of the soil factors, which are difficult to control in other production methods.
Glasshouse production requires large volumes of water and growers need to take into account the suspended and dissolved substances when planning nutritional programmes. Certain elements or compounds found within irrigation water can adversely affect plant growth and levels need to be taken into account (see table below). Others, e.g. calcium and magnesium can help meet a proportion of fertilizer needs.
