gardening

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Lush ferns and hostas grow beneath my black walnut tree.

Toxicity of black walnut trees

I have several back walnut trees growing on my property. These trees are very tall (up to 80 feet) with an open canopy. The leaves are compound; they are made up of 13-23 leaflets, each about 1-3 inches long. The nuts on the tree are covered by smooth round green husks and are the size of golf balls. When the nuts ripen, usually after falling, the husks turn brown. The brown husks ooze a dark fluid, which stains everything it touches. Black walnut trees bud out late in spring. When there is a dry summer, the trees shed leaves all summer long, so that there are few leaves left by fall. Some people claim that you cannot plant under or near black walnut trees, because these trees produce a toxin called juglone.

Juglone is released from black walnut trees through its roots and also from its leaves and the husks of its nuts. It can inhibit the growth of nearby plants and may even kill juglone-sensitive plants, such as tomatoes. It does this by inhibiting the plant’s respiration and thereby depriving the plant of needed energy for metabolic activity. The leaves of juglone-sensitive plants will yellow and wilt. If you cut down a black walnut tree, the toxicity does not disappear right away, because juglone can persist until the roots are dead and decayed. This can take 5 years or more.

 

I have beautiful shade gardens under my black walnut trees. That’s because not all plants are affected by juglone. Daffodils, bleeding heart (Dicentra), Brunnera with its big heart-shaped leaves and forget-me-not-like blue flowers, forget-me-nots (Myosotis), sweet woodroff (Gallium odoratum), and Vinca with its lovely blue flowers all bloom under the trees in early spring. Note that Vinca, often used as groundcover for shade, becomes invasive in some U.S. northeastern states, such as Connecticut, and should only be grown in restricted spaces. Iris, daylilies, Serbian bellflower (Campanula poscharskyana), and daisies bloom later under black walnut trees. Ferns and hostas thrive under these trees. My dwarf oak-leaf hydrangea and dwarf Alberta spruce are also very happy. Two arbovitaes were doing well until deer got to them this winter. I fill in the spaces between the perennials with annuals such as pansies, alyssum, blue lobelia, and impatients.

 

Plants that are known to be susceptible to juglone toxin are some peonies, azaleas, potentilla, mountain laurel, rhododendron, lilac, saucer magnolia, white birches, pine, and vegetables such as tomatoes and potatoes.

 

Juglone is also known to be toxic to earthworms, which is bad news for gardeners. On the other hand, juglone is a natural insecticide. It is known to reduce fleas of cats and dogs, if branches of the tree are placed near their bedding. You can compost walnut tree leaves, because the toxin breaks down in 2-4 weeks when exposed to air, water, and bacteria. In plain soil, breakdown may take up to 2 months.

 

Black walnut trees are not the only trees that produce juglone. Butternut, English walnut, pecan, shagbark hickory, and bitternut hickory also make juglone, but in much smaller amounts.

 

 

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Tulips amidst a blooming groundcover

Bulbs for Spring Beauty

 

Besides renovating the lawn, starting new planting beds, dividing and transplanting overgrown perennials, the most important task in fall is to plant bulbs.   There are so many varieties of tulips, daffodils, alliums, and other bulbs to choose from.

 

Tulips, known for their remarkable flowers and bright colors, make a fantastic display in spring. They are the highlight of the spring garden. These days, tulips come in all sizes, shapes and early, mid-, and late spring bloom times. There are the single, multi-flowered, double, fringed, and lily-flowered tulips. If you have vole or deer problems, you have to use protective measures to be able to enjoy tulips.

 

However, if you don’t have time to fuss with tulips, you can have easy long-lasting beauty with golden and white daffodils. All daffodils belong to the genus Narcissus and can be called either “daffodils” or “narcissi”. Jonquils are fragrant daffodils with cups shorter than their petals. All daffodils or narcissi are deer and rodent-proof, but they like well-draining soil. They hate to have wet feet. There are small and large cupped daffodils, double daffodils, miniature daffodils, fragrant ones, and ones with multiple stems per bulb. Daffodils come in white or different shades of yellow with cups ranging from white and yellow to pinkish (more of an orangey pink). Some cups have red rims. Some of the double daffodils look like puffs of fine lingerie. Daffodils that are described as good for “naturalizing” are usually very tough and do well even under less than ideal conditions. Some of my favorite “tough” daffodils include the award-winning “Ice Follies” and the late blooming small cupped daffodils belonging to the “Poeticus Narcissi” family.

 

Hyacinths, often extremely fragrant, are a great addition near a doorway or walk. Grape Hyacinths or Muscari are lovely when planted in drifts. However, my third most important bulb to plant in fall is Allium. “Allium” in Latin means “garlic”. Alliums are sun-lovers and prefer well-drained soil. Deer and rodents will not touch Allium. For the most dramatic effect, Allium is best planted in the middle or back of the border, unless it is a short cultivar like A. karativiense. The purplish or white 2-10 inch globes on up to 5 feet-long stalks make a striking display in early summer. The popular “Purple Sensation” with reddish-violet balls is one of the earliest to bloom. It’s one of my favorites. I also like the rose-purple “Gladiator” and the impressive 10 inch purple globes of Allium “Globemaster”. Even after these Alliums are finished blooming in late June, the dry globes on their stalks provide structural interest in the garden. In late fall, I cut the most perfect Alliums and place them in tall vases for indoor decoration.

 

Other bulbs to plant are snowdrops and crocuses for late winter/early spring blooms. Summer snowflake or Leukojum, which looks like snowdrops on 18-20 inch stems, blooms in late spring. Fritillaries, consisting of stalks ringed with bell-shaped flowers, come in 6 to 36 inch heights. They have distinctive hollow bulbs and come in various colors. Fritillaries are also deer and rodent-resistant.

 

Bulbs can be planted until the ground freezes, but why not get started during the pleasant early days of fall.

 

 

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The white blooms of Hydrangea aborescence next to an owl statue

 

 

How to Grow and Prune Hydrangeas for Better Blooms

 

The Hydrangea brightens the landscape like no other shrub. Its large blooms of white, pink, blue, or even lavender are striking in shaded areas. I planted a row of Hydrangea arborescence, named “Annabelle”, because “Annabelle” requires low maintenance. Despite my lack of care, I am rewarded every year with spectacular white globes of bloom. There are five main types of hydrangeas: Hydrangea aborescence or smooth hydrangea, Hydrangea macrophylla (bigleaf hydrangea), Hydrangea paniculata (panicle or Pee Gee hydrangea) and Hydrangea anomala (climbing hydrangea).

 

Hydrangea aborescence

 

One of the hardiest hydrangeas is the smooth hydrangea like “Annabelle” or “Grandiflora”. It’s frost hardy, can withstand long periods of hot dry summer without watering and can be cut to the ground in late fall or early spring. “Annabelle” has the most spectacular globes of white blooms from June to September. Sometimes after a heavy rain, the big white globes droop. The shrubs can be supported by planting several shrubs close together, so that they support each other or by encircling the shrubs with low wire fencing early in spring before the plants leaf out. Like all hydrangeas, “Annabelle” is relatively disease and pest resistant.

 

Hydrangea quercifolia

 

Another one of my favorites is the beautiful and hardy oakleaf hydrangea. It is a native plant and does well in a wooded setting or as an understory shrub. Oakleaf hydrangeas have large deeply lobed oak-like leaves and conical heads of white florets, 4-12 inches long, from July to September. The large leaves turn a deep red in fall and the older stems exfoliate to a rich cinnamon brown bark. Oakleaf hydrangeas are not as readily available at some local garden centers and you may have to order one from a garden catalog. “Snow Queen” and “Alice” grow 6-12 feet tall. Dwarf oakleaf hydrangeas grow only to about 4 feet. Flowering occurs on wood produced the previous year, so prune only right after flowering. Pruning should be minimal in contrast to the extensive pruning required of Hydrangea aborescenece.

 

Hydrangea macrophylla

 

The most popular hydrangea is Hydrangea macrophylla. This group includes the mophead and lacecap hydrangeas. The mophead hydrangeas are covered with large balls of pink or blue flowers, pink in alkaline soil and blue in acidic soil. The pink color can be obtained by adding lime. It grows 3-6 feet high and makes a great foundation plant. Unlike Hydrangea aborescence, it blooms on old wood, meaning that flower buds for the next year are formed on the previous year wood. Some of the newer cultivars like “Endless Summer” are more cold-hardy and bloom on both “old wood” and new shoots. Although beautiful, mopheads and lacecaps are less hardy than Hydrangea aborescence and require more moisture during the summer. Sometimes mopheads and lacecaps don’t bloom. The main reason for not blooming is that the buds, which were formed the year before, were killed off by frost or they were pruned off by mistake. Only prune Hydrangea macrophylla to remove dead branches or to thin the shrub.

 

Hydrangea paniculata

 

Panicle hydrangeas are the most cold-hardy hydrangeas. White flowers appear in mid-summer on 6-8 inch panicles. Unlike other hydrangeas, which need some shade; this type does well even in full sun as long as the ground remains moist. Panicle hydrangea reaches a height of 10-20 feet and you can grow it as a shrub or small tree. Prune it any time, because it blooms on new wood only.

 

Hydrangea anomala

 

Climbing hydrangea is a clinging vine with white flowers and grows up to 60 to 80 feet long. The vine can become heavy and needs a strong support. Very little pruning is required. Prune side shoots once the hydrangea is well established.

 

 

If you want stunning blooms all summer long and carefree shrubs, plant some hydrangeas. The flowers also make beautiful dried flower bouquets for indoors. The dried flowers do best when allowed to dry on the plant before picking.