Question from Jill:
My Oregon days have me indignant that I can grow blackberries here. I have Boysenberry’s canes beginning (posts and wire already in place), and these acid lovers need a PH of 5.5, which my soil test says it is not. These are in the ground in amended ground with garden soil. My leaves are a bit yellowy and I know that is a sign of a deficiency. There are too many suggestions of how to lower it (soil sulfur, cottonsead meal, ironite, pine needles), and I would like to know what I should do now, to the soil, or as a foliar spray. And then when to repeat and why (if the ph is still not low enough perhaps when tested or if the leaves will not green up?). You seem to have a plan for those of us that want to grow parts of our histories!
Answer from Pat:
Blackberries need deep, well-drained, organic soil and plenty of water. In the wild they often grow on banks and in roadside gullies, where they thrive on leaf mold from overhanging trees and moisture flowing down from above. In hot interior climate zones, provide afternoon shade.
Blackberries are subject to many pests and diseases, but healthy organic soil and no spraying with pesticides will help beneficial organisms take over and control the baddies. (Try Serenade, an organic spray if you already have disease problems. Yellow drooping leaves would be a sign.) The best thing is to start by planting healthy, disease-free plants in the first place.
Before planting blackberries, amend the soil really well with organics, such as well-aged compost. But if I had the plants you describe and they looked yellow already, I would mulch the bed with aged horse manure, water thoroughly, and see if that doesn’t produce wonders. There must be a horse farm or horse owner near you. Make sure you have a tetanus shot up to date but then go get some trash cans full of horse manure and use as a mulch on top of the ground around the berries and fruit trees. If one does this in fall the rains will wash the goodness into the ground and the manure can age right there on top of the ground. You should get the most magnificent soil, earthworms, and berries—raspberries, particularly love this treatment.
Another idea for a quick green-up of your blackberry plants, try spraying the plants with a foliar spray of a weak organic liquid fertilizer, such as a mixture of fish emulsion and Epsom salts (for magnesium). It should green the plants up. Epsom salts: Mix 1 teaspoon to a quart of water, spray on foliage. Then water really well and deeply, unless the ground is soggy already from the winter rains. (If the soil is soggy that too might be a problem since blackberries need good drainage.) Topping with horse manure once or twice a year will even solve a drainage problem eventually and make heavy clay soil highly productive. Earthworm casting tea and alfalfa tea are other organic foliar sprays you could try. These are good to pour on the ground too. (See my book for details.) Humic acid comes to mind. Humic acid mixed with kelp is a major tonic for plants releasing the goodness already in the ground and should produce incredible results. There is a product called John and Bobs Soil Optimizer that does an amazing job of greening things up. It’s expensive but is an easy way to go and great way to start, with not much work involved. So now you have all kinds of ideas. Try this or that and see what works for you and let me know results.
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