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

Coreopsis ‘Route 66’ – A Riot of Color

Posted by Hugh on July 5th, 2010

'Route 66' coreopsis

Create a hot splash in your garden this summer. Threadleaf coreopsis (Coreopsis verticillata) ‘Route 66’ is a new selection by Itsaul Nursery in Atlanta, Georgia (USDA zone 4 to 9). Coreopsis ‘Route 66’ originated in Pennsylvania (zone 5). Perennial gardeners have been planting yellow- flowered ‘Moonbeam’ and ‘Zagreb’ cultivars for over a quarter of a century.

The 2- inch wide yellow and red splotched flowers bloom continuously from June thru August. The center red pigment seems to bleed into the yellow petals. In the autumn the red tint becomes more dominant. No two blooms are ever alike. Deadheading will extend the blooming time span into October. Foliage is green and narrow (thread-like). Plant form is upright and well branched. Route 66 grows 2 to 2 1/2 feet in height, and a few inches wider than tall.

Plant in well-drained soil in full sunlight. Route 66 is a garden performer, a low maintenance perennial to enjoy in your garden for many years ahead. Route 66 exhibits exceptional plant vigor and flower power. One year old established plants demonstrate exceptional heat, drought and cold hardiness.

"pH Nutrient Creep? -You Nailed It"

Posted by Hugh on July 2nd, 2010

Photo: Foliar iron deficiency on river birch
River birch (Betula nigra) is a popular landscape tree in the Southern Appalachian region (USDA zones 6-7). The cultivars ‘Heritage’ and ‘Duraheat’ have made a good native species even better with resistance to aphid and leafhopper insects. However, river birch demands a soil pH which is moderately acid. Why?

Iron is an important minor nutrient element. If the soil pH rises (becomes less acidic), available iron becomes less available to plants. Major landscape trees also affected by “pH nutrient creep” include favorites as pin oak, willow oak, sweetgum and littleleaf linden. An old timey recommendation was putting several nails in the bottom of the hole at planting time.

Modern day solutions include: 1. adding elemental sulfur in late fall to lower the pH and next year’s new foliage should stay green all summer long; OR 2. apply iron supplying fertilizers like Ironite® or Sequestrene®, following package rates accurately; OR 3. feeding acid raising soluble fertilizers like Miracid™ or Hollytone® which contain iron.

Follow any one of these three approaches and summer color will gradually return this summer or next.

Culver’s Root (Veronicastrum)

Posted by Hugh on June 28th, 2010

‘Fascination’ with lavender purple flowers

Midwest native Culver’s root (Veronicastrum virginicum) starts the summer flowering season in my perennial garden. It naturally grows in open woods and meadows and thrives in fertile to moist soils. However, this deep rooted plant hasn’t complain about the current dry period in the Southern Appalachian region (USDA zones 6-7).

Be aware that culver’s root may grow somewhat aggressively. Over a decade in my garden, a single plant now occupies 18 square feet. It prospers in infertile clay soil. When grown in full sun, it does not require staking. I grow it in the rear of the flower bed next to another favorite – goldenrod (Solidago spp.).

The narrow floral spikes stand 3-5 feet tall, depending on the variety. White flower spikes are most common, and attract large numbers of butterflies and bees. Flowering continues over 4 to 6 weeks, the terminal blooms first and secondary laterals in late July. Floral designers love the keeping quality of the bloom spikes and lovely narrow leaves which are arranged in whorls around the branchless stems.

Culver’s root is a low maintenance perennial. It will re-bloom if old flower spikes are deadheaded. This tough prairie perennial has no serious disease or insect problems.

Agapanthus- Hardiness Issues

Posted by Hugh on June 25th, 2010

Lovely agapanthus (Lily of the Nile) is native to South Africa and is not reliably hardy in the Southern Appalachian region (zones 6 – 7). Many small tubular flowers comprise each ball -shaped (umbel) flower cluster. Tall sturdy floral scapes rise 1 to 4 feet in height, blooming from late spring into late summer depending on the cultivar. Many cultivars are available in shades of blue, purple and white.
In this region, agapanthus may be dependably grown in outdoor landscape planters which are brought inside in the fall. Agapanthus has multiple cultural issues: cold hardiness, wet wintry soils and hungry voles. Further south in zone 7-b, the crown may be covered over with several inches of leaves or mulch in late fall. The mulch is removed once the threat of spring frost has passed.
Agapanthus produces attractive glossy, strap-like green leaves, which grow from its fleshy tuberous roots. It is propagated by division of the root clumps immediately after flowering. Divide vigorous clumps every 2 to 3 years in early spring.
Agapanthus prefers a well-drained, fertile, slightly acidic soil. Locate the plant in a warm, sheltered spot under partial sun. Space plants 24 inches apart with its shallow surface roots barely visible on the ground.
Don’t permit agapanthus to dry out. Weekly watering encourages a deep extensive root system. Soggy soil is never good; the leaf tips turn yellow in a waterlogged soil.
Agapanthus requires light constant feeding in the spring and summer months using either water-soluble or slow release fertilizer with a 10-20-20 ratio. In the fall stop feeding and reduce watering to induce plant dormancy.
Pruning is done sparingly, usually to remove damaged or dead foliage before new leaves emerge in the spring.
Mealybug , red spider mite, and voles may become significant pest/critter problems.

"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).