Issue: January 31
Pruning thornless blackberries
Raspberries and blueberries for Central New Mexico
Q. We have an 8 year old thornless blackberry bush that was slow to start but now is growing as expected the past 3 years. Pruning has been inconsistent but I am led to believe pruning should be done every 2 years leaving the 1 year old growth alone. At this point I cannot determine which stalk(s) is/are 1 or 2 year old growth. When should I prune and how much to leave? Please provide counsel on pruning and please refer me to literature on care and pruning of thornless blackberry bushes. Thanks.
We live at 7,200 feet east of Albuquerque and have weather similar to Santa Fe. Ralph H. A. - Edgewood, NM
A. The canes of blackberries should be pruned every autumn or winter (after the plants are established and have begun producing berries). However, what you have heard is that it takes two years for the blackberry canes to bear.
Dr. Ron Walser, NMSU Extension Urban Small Farm Specialist who works with blackberries, explains that thornless blackberries (all blackberries, in fact) have bi-annual above ground parts and perennial below ground crowns and roots. These shoots (canes) grow during the summer, overwinter, and then produce berries the next summer, then die. In the autumn or winter after the canes have produced berries, they should be removed. The new canes that developed the previous summer will make berries next summer and must be left.
Dr. Walser describes the old (dead) canes that should be removed as those with usually having lighter colored bark than the overwintering live canes. These old canes will also have the fruiting shoots (clusters of small twigs from which you harvested berries) still attached to them. Dr. Walser says that it is best to summer prune the newly produced canes when they reach a height of about 5 feet by pinching the tip from these canes. This will cause side lateral shoots to develop. During the winter these side lateral shoots should be trimmed to about 18 inches in length.
According to Dr. Walser, some of the lack of production in earlier years may be due to cold temperatures causing damage to overwintering canes. Thornless blackberries can generally only tolerate winter temperatures down to about -5 degrees F. Some winters will be mild enough for the buds on the canes to survive and produce flowers and berries in the summer. Unfortunately, at your location some winters will be cold enough to kill the buds and you will have no crop that summer.
Q. I am trying to find out what are the best varieties of blueberries and raspberries to grow in the Los Lunas area. Through what research I have done it would seem that the Rabbiteye cultivars "Florablue" and "Powerblue" are best of the blueberries. I do not find anything in particular about the raspberries as far as heat tolerance that would make me choose one over another. Michelle H. - Los Lunas NM
A. Once again Dr. Walser has information to help you. He is growing blueberries and raspberries in variety trials at the NMSU Los Lunas Agricultural Science Center.
Dr. Walser said his trials were planted in spring of 2007. The raspberry variety that he recommends is the fall bearing Caroline cultivar. He said that at this location it is by far the best.
He also has a planting of blueberries that are doing ok. The Rabbiteye berries should do ok, but he worries about winter cold hardiness here. Rabbiteye blueberries can be damaged if the temperatures get much below about 10 degrees F. The variety that is doing the best here is the Northern Highbush cultivar "REKA". He even harvested about a cup of berries this year from plants planted in 2007. Remember that for blueberry production you will need to acidify both the soil and irrigation water. You might also want to try the thornless blackberry cultivars "Chester" and "Triple Crown". They are very productive in this area, and he recommends raspberries that do not require soil acidification (many varieties will need acidification of soil in New Mexico).
For more gardening information, visit the NMSU Extension publications World Wide Web site at http://www.cahe.nmsu.edu/pubs/_h.
Send your gardening questions to:
Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW
Los Lunas, NM 87031
Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.