Delicious, ripe, juicy blackberries are the taste of late summer, but if you have unripe blackberry fruit on your vines when you should be harvesting, it can be a major disappointment. Blackberries aren’t the pickiest plants, but not watering them adequately can lead to unripe fruit. A particular pest may also be the culprit.
Blackberry Care and Conditions
If your blackberries won’t ripen, a simple answer may be that your vines haven’t been given the right conditions or proper care. Blackberry vines need some organic material in the soil, space to grow, and a trellis or something else to climb for the best possible results.
They also need a lot of sun, light, well-drained soil, and plenty of water. Blackberries especially need a lot of water while the fruits are developing. Without enough water, they may develop as hard, unripe berries.
Why Won’t Blackberries Ripen?
If you did everything you have always done for your blackberries and you still have issues with unripe blackberry fruit, you could have a pest problem. Redberry mite is a microscopic pest that you won’t see without a magnifying glass, but that could be the root cause of blackberries not ripening on your vines.
Blackberries not turning black is a typical sign of a redberry mite infestation. These tiny creatures inject a toxic material into the fruit, which prevents ripening. Instead of turning black, the fruits, or at least some of the druplets on each fruit, will turn a bright red and fail to ripen properly. Just a few affected druplets on one fruit make the entire berry inedible.
Redberry mite will stick around on the plant through the winter and infest more vines the next year, so it is a problem to tackle immediately. Two of the most effective treatments are sulfur and horticultural oils. Apply a sulfur treatment before buds break dormancy and then again, several times, a few weeks apart, up to two weeks before harvest.
You can apply a horticultural oil after you first see the green fruit develop and continue every two to three weeks, for a total of four applications.
Talk to someone at your local nursery about which application is best and how to use it. The oil will probably cause less damage to the plants but may be less effective against the mites. Another option, of course, is to tear out your blackberry vines and start over next year.