Peaches in Greenhouses--What's This?!
I have noted before in this column that China produces roughly 45% of the world’s peaches (2007 production of 9.7 million tons on approximately 1.6 million acres). But did you know that China has approximately 30,000 acres of peaches being commercially produced in protected cultivation (i.e., energy conserving greenhouses)? This is nearly equivalent to the acreage of peaches grown outside in the states of South Carolina and Georgia combined!
These peach trees are being grown in a greenhouse in China. The top photo is before postharvest canopy removal. The bottom photo is after postharvest canopy removal.
This development was first successful at Shandong Agricultural University in the mid 1990s. A great incentive for the commercialization of this practice is the demand for fresh fruit beyond the typical peach harvest season from outdoor commercial orchards. Up to a fivefold increase in price can be obtained for fruits provided to the very early or very late-season markets. To meet the very early market window, low-chill cultivars with a very short fruit development period are selected. Jizao 518 (a 2007 release from the Zhengzhou Fruit Institute, Chinese Academy of Agricultural Sciences) is a very early, white-fleshed nectarine that ripens in 50 days and is recommended for “cultivation in infrastructure.”
A typical production system has the trees planted high density (1 meter by 2 meters) and it may remain in production like this for 10 years. To maximize greenhouse production efficiency and profitability, strawberries may be intercropped between the peach tree rows.
With space limitations, various practical measures need to be taken to maximize fruit yield and quality per unit land area while ensuring that trees don’t get too big. One such practice is called postharvest canopy removal (PCR) (see the before and after photos to the right). Basically, PCR is a modified summer pruning technique. It begins immediately after harvest with the removal of all current shoots. New shoots that emerge thereafter are “tipped” several times to stimulate flower bud production.
Besides pruning, tree size is limited by the artificial application of drought stress, root pruning, and the use of dwarfing and semi-dwarfing scion and rootstock cultivars. Other practices employed in this system include girdling in the fall, the use of hydrogen cyanamide to break dormancy in the spring, and season/cultivar specific fertilizer regimens.
Greenhouse microclimate (i.e., illumination, temperature, water, carbon dioxide-oxygen ratio, etc.) is monitored and controlled. The use of more transparent films on the outside of the structure plus the use of reflective films on the greenhouse floor enhances the light environment. Temperature regulation during bloom (72°F during the day, down to 41°F at night) and during the fruit ripening period (77°F to 86°F) can result in ripening acceleration from 10 to 50 days. Fruit quality is improved by large temperature differences between day and night. Well-insulated greenhouses that have an earth floor (and frozen soil) can hold spring temperatures cool (less than 45°F) for 50 days. Where this is utilized in the northern climates, budbreak is delayed and season extension by 10 to 30 days is achieved.
Soil moisture and relative humidity is primarily regulated by supplemental irrigation. Proper ventilation and irrigation management helps to limit foliar disease development. Efforts are currently being developed for centralized computerization to manage the greenhouse microclimate. The development and selection of new cultivars for the very early market (low chill, short fruit development period) or very late cultivars with high quality will expand the market window and help ensure ongoing profitability.
I hope to see some of these systems in action when I attend an international peach conference in Shanghai later this summer. I hope to share photos and updates in a later column.
With thanks I acknowledge the contribution of photos and information from Dr. Hongwen Huang (director and professor, South China Botanical Garden, Guangzhou) used in this column.
This column by Dr. Desmond R. Layne, “Peaches In Greenhouses--What's This?” appeared in the July 2009 issue of The American Fruit Growermagazine on page 36.