What Grows There :: Hugh Conlon, Horticulturalist, Garden Advisor, and Photographer

"My Maple Tree Is Being Invaded"

Posted by Hugh on June 21st, 2010

photo: Dr. Alan Windham, UT Plant Pathologist

The following is a real query sent to an Extension agent over the phone: “I have thousands of insects on 8 of my 10 maple trees. I fear they will kill my trees, one has already died. The insects huddle together. I am not positive they have wings, they may, but refuse to fly. Their antenna are twice as long as their body; 6 legs; body is 1/4” long, blackish, the body tapers to a pointed rear end. I see multiple groups on my tree branches. Smaller, shorter ones have white lines across body. They are the younger ones.
Barklice also called psocids (Order Psocoptera feed on mold/fungi etc. on the bark). They are harmless and tend to aggregate. There are immatures (without wings) and adult (winged) present. The photo shows the winged barklice adults.
Lesson learned: not all insects are harmful, ready to injure your garden plants. Are you curious what killed the homeowner’s other maple tree last year? I am too, but he cut it down before anyone could diagnose it.
Contact your local county Extension office for gardening assistance.

New Hardier Gardenias

Posted by Hugh on June 18th, 2010

Old fashioned gardenias or cape jasmines (Gardenia jasminoides) are reliably hardy in USDA zones 7-b and 8. Plants require immediate protection when the outdoor temperatures dip below 15 to 20 degrees.

The new hardier cultivars are compact growers, 2-4 feet tall and 3-4 feet wide. ‘Frost Proof’, Crown Jewel™, and Heaven Scent™ are three promising hardy cultivars to try in USDA zone 7-a. All three strut great thick, high gloss, dark green foliage.

Choose a garden location with good air circulation. Morning sunlight and afternoon shade is the rule. Plant gardenias in a well-drained acidic soil, and generously amended with compost. Water plants when dry and never overwater them. Acute leaf drop occurs in poorly drained soil. Fertilize once a year after the heaviest blooming cycle in June has past.

Fully capture gardenia’s fragrance by planting in a garden spot or a container nearby a deck or patio. Individual blossoms generally last a few days. Flower loss may be rapid following a wind and rain storm.

Prune gardenias is immediately after blooming in early July. Remove all dead or unsightly shoots anytime you see them. Additional scattered blooms may occur anytime during the growing season. Late pruning should be avoided in the fall as next year’s flower buds are being set.

White flies and flower thrips are major nemesis of gardenias. Bayer Advanced Tree and Shrub™ (soil drench) and horticultural oil (spray) should clean up most pest problems. Always read the pesticide label before using!

Smaller Southern Magnolias

Posted by Hugh on June 13th, 2010

The grand Southern magnolia (Magnolia grandiflora) thrives here in the southern Appalachian region and along the Eastern seaboard as far north as Boston (USDA zones 6-9). Most homeowners do not have room enough to grow this 60-70 foot arboreal aristocrat.

Compact forms are available that need less than half the space. The ivory white flowers are fragrant and 25% smaller than full sized trees. Blooms open individually, not all at once, from late May thru the summer months. The most popular compact cultivar is ‘Little Gem’. It grows to a height and width of 40 x 35 feet in 25-30 years. Others include ‘Hasse’ (45 x 20 feet) and Teddy Bear® (30? x 20 feet).

The newest introduction is ‘Kay Parris’ with exquisite polished green wavy leaves and mahogany brown beneath. The parents of ‘Kay Parris’ are ‘Little Gem’ and ‘Bracken’s Brown Beauty’. As a young tree, ‘Kay Parris’ exhibits an upright, narrow (columnar) form, rating it a great evergreen tree for a small garden space.

Southern magnolia is planted from late winter through early fall in well-drained, organically amended soil in a full to partially (6 hours minimum) sunny area. Tree rarely has disease and insect issues.

Squash Vine Borer

Posted by Hugh on June 10th, 2010

photo credit: Dr. Alan Windham, Univ. of TN Extension Plant Pathologist

Squash vine borer (SVB) damages squash, gourds, and pumpkins. Cucumbers and melons are usually not attacked by the SVB.

The adult SVB is a clear-winged moth. The 1 inch long adult moth is commonly mistaken for a wasp. Its abdomen is ringed with orange and black. Females lay oval brownish eggs on plants in late May or early June. The borers tunnel into stems near the soil and feed on the plant. Excrement is visible near points of entry on the stem when larvae are feeding. Heavy feeding causes the infested vine(s) to wilt and die.

Select a variety which is SVB tolerant. Also, cover emerging plants with row covers to reduce possible damage. Remove row covers when the plants begin to bloom to permit insect pollination. Stagger new plantings every 2-3 weeks to avoid SVB populations.

Some gardeners cover the main stem with pantyhose to prevent egg laying by adults. Infested stems can be split and larvae removed. Add a spade-full of moist soil over damaged stems to encourage new root growth. Insecticides must be applied prior to borers entering into the stem.

Insecticides containing carbaryl, bifenthrin, spinosad, or permethrin are effective against SVB. Apply an insecticide every 5-7 days. Please read the pesticide label before applying.

Vitex ‘Shoal Creek’

Posted by Hugh on June 9th, 2010

Chastetree (Vitex agnus-castus) is an 8-10 foot deciduous shrub or 12-15 foot tall small tree (hardiness zone 6-b thru 8). Branching habit is dense and vase-shaped (upright). It blooms over most of the summer, from June thru late August. Its 12-18 inch long blue-violet flower spikes exude a slight herbal fragrance.

‘Shoal Creek’ is a leading cultivar. Cold hardiness appears better than most, although this has yet to be proven. The finger-like compound leaves are covered with pubescent hairs. Summer foliage color is grey-green, with a faint bluish cast more visible in May and June. Its disease resistant foliage and butterfly magnetism rates this vitex in a class on its own. Foliage is highly deer resistant.

Stem die-back may occur in a cold winter, but this fast grower recovers rapidly. Since flowering occurs on new growth, prune off all dead, injured and crowded branches before the start of May. Vitex prefers full sun, but will tolerate part sun. Plant in a loose, well-drained soil and keep adequately watered during the first year. Afterwards, vitex possesses very good drought tolerance.

Catalpa Both Loved And Hated

Posted by Hugh on June 8th, 2010

Northern catalpa or Indian cigar tree (Catalpa speciosa) has enormous presence in any landscape setting (USDA hardiness zones 4-8). Finding a 70 – 80 foot tree with a massive trunk and thick sinuous limbs is not unusual from Ohio south thru Tennessee.

In summer its huge heart –shaped, pale green leaves may be easily reach 8 – 12 inches long and wide. Birds often seek shelter under its foliage cover. Catalpa offers a spectacular floral display lasting two weeks and more in May. The enormous coarse textured foliage offers some tropical appeal.

Numerous two- inch long white flowers are borne on large terminal spikes, many unfortunately hidden beneath the enormous catalpa leaves. Each flower has small gold spots within its frilly edged corolla. Narrow cylindrical cigar fruits, 8 – 15 inches in length are easily visible in the fall and winter months.

Catalpa trees are often visited by the catalpa sphinx moth whose larvae (caterpillars) are prized by fishermen for bait. Hummingbirds are a major pollinator, attracted to the floral nectar.

The tree is common along roadsides, particularly in bottomlands, often growing in poor soil. For most residential neighborhoods catalpa’s fast growth rate and enormous size make it of limited value. The brittleness of small limbs (twigs) requires almost constant clean-up around lawn areas.

Southern catalpa (C. bignonioides), another native form, grows smaller, averaging 35-50 feet in height (zones 5-9).

Indian Pink is a Summer Sizzler

Posted by Hugh on June 6th, 2010

Indian pink (Spigelia marilandica) is a strikingly beautiful native wildflower here in the southern Appalachian region (USDA zone 6 -7). Beginning in late May, bright red tubular flowers flare open, crowned by five sharply pointed pale yellow reflexed lobes (see photo).

Indian pink prospers around rich moist open woodland areas. The well-drained soil should have a pH range between 6.5 to 7.0. Generously amend a partially sunny site with compost or peat to stimulate plant vigor and repeat flowering. Healthy plants grow 12-18 inches tall. Spigelia leaves attach directly to the main stem without petioles.

Indian pink is slow growing at first, taking two to three years to reach maximum floral potential. Planting five or more in a clump creates a showier display. Eventually, a healthy grouping will colonize. Bloom time is lengthened by swift removal of the old spent flowers.

Indian pink often blooms for a brief second interval in late summer when soil moisture is plentiful. Plant debris mostly disappears before winter sets in. The brightly colored flowers attract numerous pollinating insects and hummingbirds. No disease and pest problems are observed.

Hardy Rosemary

Posted by Hugh on May 30th, 2010

Rosemary (Rosmarinus officinalis) ‘Arp’ is winter hardy in southern Appalachian (USDA hardiness zones 6-b and 7-a) gardens for two decades , including some very cold winters. Other rosemary cultivars which have succeeded include ‘Athens Blue Spires’, ‘Hardy Hill’, and ‘Salem’.

Locate a site with a “micro-climate” advantage such as next to a driveway or along the southside of a red brick home or a dark colored garage wall. Here winter temperatures vary by a few degrees warmer. Dark asphalt pavement absorbs and retains heat. Next to large bodies of water, such as a swimming pool and a water garden, may also be slightly warmer in the winter.

Plant rosemary in well-drained soil and in full direct sunlight. With rosemary and other semi-tender herbs, winter kill may also be caused by wet, soggy soil rather than cold.

‘Arp’ matures a handsome woody shrub with fine textured foliage. It grows 3-4 feet tall and wide, and blooms in early spring. The blue flowers are small and attract lots of insect activity.

Dreaded Rose Rosette Disease

Posted by Hugh on May 24th, 2010

No rose is resistant to this deadly virus disease. Symptoms of rose rosette disease (photo) vary greatly from the species or cultivar planted. Leaves may be small, distorted, and exhibit a conspicuous red pigmentation. Diseased canes may also be noticeably thicker than others around them, and/or may grow in a spiral pattern.

Multi-flora roses, a noxious shrubby weed, are most susceptible and often are first to contract the disease. Very small eriophyid mites transmit rose rosette disease by feeding off the plants which are already infected. Mites transmit the virus to healthy roses nearby. Control measures must be rapid and decisive.

Insect spraying will help. Spray roses with Sevin (carbaryl) insecticide for partial control of the eriophyid mite. Eliminate multi-floral roses within 300 feet from any rose plantings, preferably from all surrounding yards and gardens.

Prune out all diseased and suspected canes. Remove all prunings immediately from the property. If symptoms reappear on new re-growth canes, remove the bush from the property. When planting roses, space them far enough apart that foliage does not touch neighboring plants.

Lovely Lavender

Posted by Hugh on May 22nd, 2010

photo: ‘Munstead’ lavender

Lavender is a hardy shrub that thrives in dry alkaline soil. Lavender is commonly used as a food seasoning, a culinary substitute for rosemary. Dried flowers are crafted into table arrangements and lavender fragrance is captured in sachets and potpourris. Lavender is used to store clothes as a moth repellent. Some people store some under a pillow as a sleep aid, a form of “aromatherapy”. Bees produce a high-quality honey from the flower nectar.

There are two kinds of lavender. The shorter-growing cultivars of English lavender (Lavandula angustifolia) like ‘Munstead’, ‘Hidcote’, and ‘Lady Lavender’, flower in mid-May for one month. When cutback, English lavender blooms again in August. The taller more vigorous French lavender (recommend cultivars ‘Provenance’, ‘Grosso’ and ‘Super’) flowers only once in late June. For lavender oil production, I recommend ‘Super’.

Lavender is only successful planted in soil that is exceptionally well drained. An ideal soil pH range is 6.5 – 7.2. Grow on raised mounds and space plants 3 feet apart in the row and 6-8 feet in the row, if grown commercially. Other than for harvesting, prune plants back one-third in a ball shape in September. Lavender has very few disease and pests problems and possesses high drought tolerance.