In recent years, the developed world has become very aware of the health-promoting properties of the ‘berryfruit’ group. This awareness has created a strong world market for product and, correspondingly, a very vigorous expansion in the berryfruit sector. Similarly, in New Zealand, the berryfruit industry is enjoying strong growth.
The fruit types classified by horticulturalists under the heading ‘berryfruit’ include a diversity of species and genera. It includes many of the smaller members of the botanical grouping, the false fruits (e.g. strawberry, boysenberries, raspberries, rosehip, mulberry) and also many of the smaller members of the true berry fruits (e.g. blackcurrant, gooseberry, blueberry, cranberry).
Given the right climates and soils berryfruit offer excellent potential for profit – even from quite modest areas of land. The berryfruit species each have their own special (and diverse) production requirements – some require very good drainage (e.g. strawberries) while others are naturally bog plants (e.g. cranberries). The most common berryfruit crops in New Zealand are strawberries, blackcurrants, boysenberries, raspberries and blueberries.
All berryfruit require adequate water to size the fruit but since they are all shallow rooting, poor drainage and associated anaerobic conditions are not tolerated by any of them. Blackcurrants and boysenberries are more tolerant of wet conditions than are blueberries and cranberries, while strawberries and raspberries are both very sensitive to water logging and its associated diseases. Thus the use of gypsum to remedy poor drainage in heavy or compacted soils is particularly recommended for the latter.
Specific calcium-deficiency storage disorders are not as familiar in berryfruit species as they are, say, in apples. However, berryfruit do not store well and there is evidence that inadequate fruit calcium is associated with reduced shelf life, reduced firmness and more rapid softening in storage. There is also some evidence that good calcium nutrition can enhance fruit size. Lime or dolomite can be used to raise soil pH and to provide soil calcium but where pH adjustment is not required (most berryfruit like acid soils) gypsum is the better calcium source.
Strawberries Strawberries are best grown in a soil of pH between 5.0 and 6.5 with the higher value being best with sandy-textured soils and the lower one with finer textured soils. Their shallow feeder roots do not tolerate waterlogging and the diseases associated with wet conditions. Because it raises soil pH, lime should not be used on strawberries except in cases of extreme soil acidity. Gypsum is ideal both to improve soil structure, thus reducing wet-feet problems, and to provide a source of calcium.
Blackcurrants, boysenberries and raspberries
Blackberries These species are surface rooting and prefer a moist yet well-drained and fertile soil that provides free root-run. The soil must have adequate water holding capacity to cope with dry periods. These species do best with a soil pH between 5.4 and 7.0. Again, gypsum is ideal for use on these crops. Raspberries are more susceptible to wet-feet problems than boysenberries or blackcurrants.
Blueberries and cranberries
Blueberries Blueberries and cranberries are closely related species. They both have shallow root systems that are very fibrous but devoid of root hairs. This characteristic makes them very sensitive to fluctuations in soil water. Blueberries and cranberries are typically grown on peaty soils that are very high in organic matter, but may be poorly drained due to a high water-table. For this reason, the addition of gypsum to improve or modify soil structure is unlikely to be beneficial.
The growing of blueberries on mineral soils is relatively new. Where mineral soils are used, they are usually modified by the addition of organic matter in a form such as sawdust. Growers are well advised to avoid clay soils where drainage problems might arise, but on marginal soils gypsum is a valuable amendment to address structure and drainage issues.
Soil pH requirements are rather acid for these species, the optimum range being 4.5-4.8 for blueberry and 4.0-5.0 for cranberry. The calcium requirement of these plants is generally met by the calcium content of other fertilisers. Sulphur requirements are also usually met by fertilisers such as sulphate of ammonia, or compound materials.