Good neighbors for walnuts

Q We bought a home with black walnut trees in the yard. They're lovely trees, but I have trouble growing things near them. I've heard that black walnuts are poisonous to other plants. Is that true? Which part is poisonous -- the wood, leaves or roots? Are there any plants that will grow close to them?

A Unfortunately, all parts of a black walnut tree contain juglone, a substance that's toxic to many other plants. Juglone is exuded into the soil through the roots, which is the primary reason susceptible plants can't be grown near black walnut trees. Smaller amounts of juglone are released into the soil as leaves decay and when rainfall filters through the foliage and down the bark. And because juglone is released as plant parts break down, it's not a good idea to use black walnut leaves or chipped bark as mulch unless you're sure the plants you mulch can tolerate proximity to black walnuts.

However, black walnut trees are native throughout Minnesota's woodlands, so it makes sense that a number of wildflowers grow under them. There also are some annuals and perennials, some spring bulbs and even some vegetables that grow well near black walnuts.

Master gardeners from Renville County compiled a list of plants that will grow under black walnuts, based on their own experience and observations. Their list includes:

Annuals: calendulas, hollyhocks, morning glories, pansies, wax begonias, zinnias.

Perennials: astilbe, beebalm, cinnamon fern, coral bells, daylilies, garden phlox, hosta, lamb's ear, sedum.

Wildflowers: bloodroot, Dutchman's-breeches, jack-in-the-pulpit, lungwort, spring beauty, violets.

Woody plants: black raspberries, red cedars, wild grapes.

Turf grass: Kentucky bluegrass (provided the site isn't too shady).

Vegetables: melons, beans, carrots, corn, squash. (Vegetables should be planted far enough from the tree so they get at least six hours of sun daily and don't have to compete with the tree for water and nutrients.)

For a longer list, go to www.extension.umn.edu/distribution/horticulture/components/8464-30uabwt.pdf.

How about them apples? Q I planted a Honeycrisp apple tree about six years ago. It's getting quite large, but has never produced flowers or fruit. Does it need to be near another apple tree before it will bloom?

While dwarf apple trees usually begin to bear fruit very early, my guess is that yours is a standard. A standard tree may not bear until it has been in the landscape seven to ten years. The more shade an apple tree receives, the slower it will be to bloom. Excess fertilizer can also stimulate trunk and branch growth, slowing the onset of flower bud production.

Once the tree does bloom, you'll only get fruit if there are other apples or ornamental crabapples in your neighborhood so bees can transfer pollen to your blossoms. Unless your yard is isolated, chances are good that you won't need to plant a second variety of apple in order to get fruit. DEB

Brown tips on yews Q Why do the tips of my Japanese yews turn brown and dry each winter? I cut them off and the new green growth is fine right into winter. Then by spring, they're brown and dry again. How can I keep them green and healthy?

A There are several explanations for why you're having trouble with your yews.

Ideally, yews should be planted where they're protected from harsh winter sun. However, if your trees got too much direct sunlight in winter, you'd probably see more than just the tips drying out. Large portions of the plants might suffer from winter burn, particularly on the side most exposed to the sun.

Whatever the reason, it's important to water yews thoroughly throughout the growing season, not just in autumn, so they're well hydrated going into winter. Once the ground freezes, their roots are no longer able to pull water from the soil to replace moisture lost to winter winds and drying sunlight. Mulching around your yews also helps by reducing evaporation from the soil and keeping the soil from freezing as early as it might otherwise, which allows you to water longer.

The good news is that yews, unlike pines or spruce, continue to grow all season long. So even if you do have to trim off brown tips each spring, new growth should appear soon and the plants should look good again.