My neighbours have a 35 ‘ Black walnut (Juglans nigra) tree that I believe is affecting my once flourishing raspberry patch, which has been in decline for about 8-10 years. Is this tree the likely cause for the decline and is there anything I can do to mitigate the damage?
It is true that the Black walnut tree can cause significant damage to companion plants due to the juglone toxicity which is especially concentrated in their roots, buds and nut hulls. This toxin can cause plants nearby to turn yellow, wilt and sometimes die.
However, black raspberry is considered relatively resistant and tolerant to juglone; depending on the specific variety of raspberry, there will be a varying degree of sensitivity. The other possibility for the decline is the canopy itself of a 35′ tree, as raspberry needs full sun. As well, the soil for the now mature raspberry patch may be in need of some amendment and the patch may need a good thinning and pruning to help stimulate fruit production.
It is recommended that pruning for summer bearing plants occurs in the fall and removes all but the strongest canes and that pruning for ever-bearing plants occur also in the fall but consists of mowing or shearing to the ground.
An excellent source of information regarding the detailed care of dozens of cultivars of raspberries is: