Q: I'm trying to identify the tree in the photo. I've been told that the nuts are not edible. Can you help? — Scott Bundy
A: The tree in the photo is black walnut, Juglans nigra, and it's a well-adapted tree for the Upper Midwest. The walnuts, located inside the green husk, are completely edible when ripe. The green fruit surrounding the nut contains a dye that easily stains the hands brown, so gloves are advised when working with the fruits and enclosed nuts. The nut meat inside the walnut is very tasty, but doesn't shell out as easily as other commercial walnuts. Black walnut fudge is delicious, by the way, and black walnut trees are highly prized for their beautiful lumber.
Black walnut trees release a chemical into the soil called juglone, which is toxic to some non-walnut plants in the near vicinity. Not all plant types are affected, but sensitive plants can be stunted or killed, including tomato, pepper, eggplant, potato, lilac and peony. The toxic effect can extend 50 to 80 feet outward from the tree trunk.
Q: We have a row of 22 spruce trees as a privacy screen between our home and the neighbors. The spruce trees are dying from needle cast disease. Could we remove the spruce trees and plant Green Giant Arborvitae for a screen that will grow quickly? — Betty Menholt, Felton, Minn.
A: Green Giant Arborvitae is a fairly new hybrid arborvitae, and is fast-growing where it is adapted, but research indicates it's only reliably winter-hardy in zone 5, making its survival difficult in our zones 3 and 4.
A better choice for our region is Techny Arborvitae, which has a history of reliability and makes an excellent screen singly or in a row. Techny develops a large teardrop shape, easily reaching 25 to 35 feet tall and 12 feet wide at the base. I can vouch for their performance, as we once had a screening row of Techny.
Techny is extremely winter-hardy and is resistant to winter burn, insects and disease. For a solid row, space Techny 8 to 12 feet apart. You'll find them at many garden centers.
Q: As we're picking our raspberries, we've noticed small white worms on and in the berries. Is there something I can spray? I don't want to spray anything that will kill bees as they are very active in the patch. — Merlin L Christensen, Waubun, Minn.
A: Raspberries and many other homegrown fruits have been plagued in recent years by two insects: small black picnic beetles, also known as sap beetles, and the small white larvae of the spotted winged drosophila fruit fly. The white worms you describe are likely these.
The fruit fly lays eggs in fruit, which hatch into the larvae, which feed on and in ripening fruit. The fruit becomes soft, and finding larvae makes the fruit unappetizing. Applying insecticides to ripening fruit like raspberries is difficult because the products have a certain number of waiting days required between application and harvest, indicated on the label.
This waiting period is too long for some common insecticides, but a product being widely recommended is spinosad, which has a short interval of three days between application and harvest of raspberries. Spinosad is even approved for organic growers, and is less harmful to bees than insecticides with long residuals.