Methods of growing raspberries vary from country to country, partly because of differences in labour availability, degree of mechanisation, and type of cultivar. Information is needed on the extent to which these constraints reduce yield below the potential.
Experiments in Scotland have shown that yield reaches a plateau at a cane density of about 8 - 9 per metre of row, that productivity increases with closer between-row spacing down to the closest investigated (180 cm), and that the greater the tipping height the greater the yield. Neither water supply nor mineral nutrition provides a satisfactory explanation of yield differences in these experiments. The results are consistent with the idea that light interception is the critical factor.
The optimum distribution of light between the fruiting and vegetative phases is not known, though results of vigour control experiments suggests that it is not ideal in some existing cultivars. When the phases are separated in time (biennial cropping) there appears to be an unavoidable reduction in light capture relative to that in annually-cropped plantations. Until more is known about the relative responses of primocane and fruiting canes to light regimes it will be difficult to predict the ideal combination of genotype and cultural method. Present evidence suggests that the aim should be to produce cultivars with a vigorous growth habit which can be controlled by cultural methods to a degree appropriate to local conditions.