Carobs are reasonably well suited to grow in large areas of southern Australia – mainly on soils that are well drained and aerated, including sands, clay loams, limestone, and alkaline or moderately acid soils. Temperatures under minus 4 degrees centigrade can injure or kill young trees, and severely damage the branches as well as new shoots and flowers of mature trees.
Research into the carob’s optimum water use requirements has yet to be done; however, in general it is likely that the minimum rainfall for carobs should not be less than about 500 mm per year, with supplemental irrigation a certain benefit. Carobs grown in lower rainfall areas are considerably more susceptible to climate change. It is important to quickly establish deep-rooting patterns, particularly in the early years of their growth – lessening the time required to bear commercial crops, reducing alternate bearing and higher average yields.
Timely application of orchard management practices for carobs is the same as other tree crops from planting to fertilising, irrigating, pruning and weed control. In the pre-planting phase, it is necessary to decide well in advance whether to direct seed, or to obtain seedlings and then field graft them, or to do as increasing numbers of landholders are doing – purchase trees that are already grafted with known cultivars. Only Limestone Nursery in Broken Hill NSW specialises in grafted carobs (www.carobtrees.com). Some 15 varieties are available from this nursery, amongst which are 11 of the best European and American selections that were brought to Australia by Dr Henry Esbenshade in the early 1980s.
There are numerous benefits from growing grafted trees which include not only a shorter time lag before carob pod production begins, but knowledge of the variety’s preferred environmental conditions, the chemical qualities of the pods (eg sugar and tannin levels), the timing of pod ripening (whether early, mid or late summer season), and the average yield which can be expected. In general, grafted trees begin to bear within 3 – 4 years and yields of from 60 – 100 kg per tree can be harvested by about the tenth year. The author has harvested old trees in Valencia Spain that yielded 250 – 300 kg each.
The inter-planting of female pod-bearing varieties with hermaphrodites (combined male & female flowers) as pollinators is a proven strategy. There are varying estimations of the optimal ratio of female / pollinator whether male or hermaphrodite – a ratio of 8 females to one male or hermaphrodite is common in the Mediterranean region (Battalle and Tous 1997 Carob Tree. International Plant Genetic Resources Institute, Rome – copies available from Carobs Australia Inc). In this country, successful full row plantings have been reported with a ratio of 1 hermaphrodite (producing pods and providing pollination) to 3 females.
Trial plantings on varying soil types of a range of varieties is recommended to assess best-bet site-specific options for growing varieties that yield regularly well. In-row and between-row spacing’s are generally set at 10 x 10 metres (or a metre or so less in either or both directions) to allow for mechanical harvesting of mature trees. Orchard geometry should be varied to fit topography & soil changes, and to optimise the economic application of water through drip or micro-spray. Windbreaks should be planted to improve pollination by bees & other insects, and to lessen evapotranspiration rates for sustainable water use.
Contact Carobs Australia for more details