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

All About Mulches

Posted by Hugh on December 10th, 2014

Delivery of Hardwood Bark Mulch

Pine needle mulch around azaleas at Callaway Gardens

Mulches aid in retaining soil moisture and reducing weeding chores. Over the years organically-based mulches gradually improve garden soils. Organic mulches are basically recycled bark, branches, twigs and leaves (including needles). Frequently they are organic by-products from the logging industry. Grass clippings and straw are also mulch sources. Hay is usually full of weed seeds which defeats the purpose for using it.

Over the years pine bark, nuggets, and needles tend to slightly acidify as they decompose in the soil. Oak leaves also tend to be acidic. These mulches are highly beneficial around acidic-loving shrubs such as blueberries, azaleas, rhododendrons, mountain laurels (Kalmia spp.), and others. Hardwood based mulches, ground from wood waste from most trees and evergreens, turn the soil slightly alkaline (raise soil pH) as it decomposes.

Fall applied mulches tend to act as a warming blanket, trapping in ground heat. The mulch blanket prolongs root growth in autumn by many weeks. Spring applied mulches may retard plant growth around newly planted perennials and annuals. Year-round mulching keeps ground surface temperatures cooler that benefits certain tree and shrub species. Never pile mulch up against the trunks of trees and shrubs as it often results in wood decays and/or formation of above ground roots.

Mulch should not be spread around recently planted fruit (and maple) trees unless the trunks have been protected by rodent guards around their base. In the winter pine voles will nest under the mulch and gnaw on the sugary sap of the fruit trees. Fruit trees after two years no longer need to be protected.

Finally, a warning about mulch quality. If a mulch pile is excessively steamy (over 100 ºF) or exudes a distinct alcohol smell, do not purchase or accept delivery. The product will likely burn young landscape plants, particularly herbaceous perennials and annuals. Yes, mulches may attract termites, carpenter ants and other wood boring insects.

Trees And Shrubs That Grow In Poorly Drained Soils

Posted by Hugh on November 17th, 2014

Surface Knees of Bald Cypress Tree at Longwood Gardens, Kennett Square, PA

If a section of your landscape is poorly drained, there are a number of trees and shrubs that will adapt over time to short periods of wet or soggy soils. Plant roots must survive in low oxygen soils. Your choices of plants are not lengthy; few landscape plants will not tolerate root suffocation for even brief intervals of time.

On landscaping sites with poor drainage, start with trees and shrubs that native to wet bottomland areas. They make the best candidates. When planting tolerant trees and shrub species, plants must have a period of time to adapt to the flooded, low oxygen soils. They are likely shallow-rooted and require staking for initial support. Over time, plants will develop physiological and anatomical features to tolerate poor drainage. For example, bald cypress (Taxodium distichum) develops “knees” on the ground surface to capture air.

Plant scientists at North Carolina State University in Raleigh, NC recommend starting with small plants that have been grown on poorly drained sites. It also helps to create raised beds, swales, grassed waterways, and drainage lines that can divert excess water away from planting sites. The following list is not complete, but does include some great plants. Many are excellent choices for inclusion in rain garden sites.

Tree List:

Red Maple (Acer rubrum)

Silver maple (Acer saccharinum)

Pawpaw (Asimina triloba)

River birch (Betula nigra)

Hackberry (Celtis occidentalis)

Green ash (Fraxinus pensylvanica)

Eastern redcedar (Juniperus virginana)

Sweetgum (Liquidambar styraciflua)

Sweetbay magnolia (Magnolia virginiana)

Blackgum, tupelo (Nyssa sylvatica)

Swamp white oak (Quercus bicolor)

Bur Oak (Quercus macrocarpa)

Willow oak (Quercus phellos)

London plantree (Platanus x acerfolia)

Willows (Salix spp.) -tree and shrub forms

Bald cypress (Taxodium distichum)

Eastern arborvitae (Thuja occidentalis)

American Linden (Tilia americana)

Canadian hemlock (Tsuga canadensis)

American elm (Ulmus americana)

Shrub List:
Summersweet, sweet pepper bush (Clethra alnifolia)

Buttonbush (Cephalanthus occidentalis)

Red osier dogwood (Cornus sericea)

Common witchhazel (Hamamelis virginiana)
Possumhaw (Ilex decidua)

Winterberry holly (Ilex verticillata)

Yaupon holly (Ilex vomitoria)

Virginia sweetspire (Itea virginica)

Ninebark (Physocarpus opulifolius)

Dappled willow (Salix integra ‘Hakuro Nishiki’)

American elderberry (Sambucus canadensis)

Snowberry (Symphoricarpos alba)

Coralberry (Symphoricarpos orbiculatus)

Arrowwood (Viburnum dentatum)

Nannyberry (Viburnum lentago)

Are Your Trees Hazardous?

Posted by Hugh on October 28th, 2014

Mature Tree Removed By Certified Arborist

Silver Maple tree rotted at base

Is a hazardous tree lurking in your yard, ready to fall on your house or car? Take a few minutes to inspect trees on your property. Peek over the fence at your neighbor’s trees as well.

Some property owners have an unnatural fear of trees. Well-shaped landscape trees with no dead wood, good growth rate, and a full canopy (top) are rarely a risk. Yes, it’s true that the healthiest of trees are likely to be injured in a “category” hurricane or tornado.

Tree care goes along with tree ownership. Tree health, like people health, changes as they age. Middle-aged trees are less hazardous than mature trees. Age plus a category storm may inflict enough damage to render a tree hazardous.

Location is another factor. A tree deemed hazardous, but not growing near people, houses, and autos, is unlikely to inflict serious injury when it falls. Your insurance company may never hear from you. Trees in a public park, along streets, or in residential zones should be inspected, then pruned or removed.

Trees may show decay or cavities along the main trunk(s) and branches, and timely pruning usually cures most ills. It’s like going to a dentist. A cavity represents wood decay and branch weakness. Decay can be slowed by cleaning out the wound and spraying a pesticide to prevent wood boring insects from habitating.

Different tree species possess different mechanical strengths and decay mechanisms. Weak wooded species considered potentially hazardous include silver maple (Acer saccharinum), cottonwood and hybrid poplars (Populus spp.), willows (Salix spp.), boxelder (Acer negundo), ornamental pears (Pyrus calleryana), and tree-of-heaven (Ailanthus altissima).

A certified arborist can measure the extent of the tree decay using a Resistograph®. A hollow tree cavity is not always hazardous. Tree cavities that are surrounded by at least one inch of solid wood per six inches of tree diameter are unlikely to fail.

Hire only a certified, licensed and insured arborist. Certification is awarded through the International Society of Arboriculture (ISA) following extensive study and testing.

Prep Garden Soil In The Fall

Posted by Hugh on October 22nd, 2014

Pine bark amendment at a nursery

Often, spring arrives with too many gardening chores to handle. Some work can be shifted to the fall. Since a garden is only as good as its soil, fall is a good time to till your garden or to construct new beds. Add soil amendments such as deciduous leaves and pine needles which nature is providing for free. Till amendments into the soil with a shovel, multi-tined garden fork, or rototiller.

You may add organic nitrogen sources such as blood meal, animal manures (either packaged or fresh from a nearby farm). Fresh manure may be too hot to use in the spring, but will lose its hot urea properties over the winter. Incorporate digested (decayed) compost pile(s) into your garden soil. Soil microbes do most of the work decaying the organic additives over winter.

Shredded leaves, eggshells, coffee grounds, and fruit peels are all great soil additives; most will break down before spring planting season arrives. Caveat: huge quantities of undigested materials can rob the garden plants of nitrogen next summer. In such cases, you may need to add lots more fertilizer to feed both the garden plants and soil microbes.

The final step before spring is test the garden soil at a state soil lab operated by your state land grant university. Some full-service garden centers may also provide soil testing. Collect the soil sample before the lab’s mad spring rush begins. The local county or area Extension agent will interpret the diagnostic results for you.

The amended soil will be a lot easier to plant into next spring. Fall tilling also buries weeds and weed seeds to reduce this chore next summer.

Evergreens For Wet Soggy Soils

Posted by Hugh on October 19th, 2014

Emerald™ arborvitae at Daniel Stowe Botanical Garden, Gastonia, NC

Most needle evergreens falter in moist soggy soils. These sites usually have a heavy clay or fine particle sand content. Some arborvitaes (Thuja spp.) and Atlantic white cedar (Chamaecyparis thyoides) tolerate temporary wet soggy conditions better than most evergreens (USDA hardiness zones 3-8). An assortment of shapes, sizes and colors are available. All are U.S. natives.

Eastern arborvitae (T. occidentalis) tolerates dry to boggy wet sites. Emerald™ and ‘DeGroot Spire’ is two popular favorites, growing 12-15 feet or 8 feet tall respectively over 15-20 years. The scale- like foliage is uniquely twisted and spiraled. ‘Hetz Midget’ or ‘Tiny Tim’ are dwarf globe or ball forms that grow 12 inches tall and 16 inches wide. The light green scaly foliage turns bronze over winter.

Western arborvitae (T. plicata)) also tolerates tight wet soils. It grows tall and is fast-growing with a tightly pyramidal growth habit. Most popular is the hybrid ‘Green Giant’ (T. plicata x T. standishii) cultivar. Summer foliage is dark glossy green and bronzes over winter. Green Giant grows to a mature height of 50-60 feet tall and 8-10 feet wide. For something very different, ‘Whipcord’ is a dwarf cultivar with unusual thread-like branches and an arching plant habit. It grows to only 2 feet tall by 3 feet wide in 10 years.

Atlantic white cedar (C. thyoides) (zones 5-9) is often observed growing on soggy sandy sites, but dislike clay soils. Winter foliage turns a deep plum color and back to green by the start of spring.

Three popular selections of C. thyoides include:

‘Rubicon’, aka ‘Red Star’ – upright dense form with star-like foliage (6 feet tall by 2 feet wide).

‘Heatherbun’ – compact, globe-shaped form (6 to 8 feet tall by 4-5 feet wide).

‘Shiva’ – dwarf multi-stemmed form with upright spreading branches and silvery lacy foliage (5 feet tall by 4 feet wide) .

Shrubs You Should Not Prune In Fall Season

Posted by Hugh on October 10th, 2014

Flowering quince (left) and Forsythia (right)

Why would anyone prune spring flowering shrubs in the autumn season? After a long cold winter, why miss out on the delightful fragrance of lilac and viburnum flowers the following spring?

Predicting how cold, warm, or dry the coming winter season is rarely possible. Pruning cuts are wounds and weather extremes may cause injury to the previously-cut branches.

Partial list of spring flowering shrubs:
Azaleas (Rhododendron)
Beautybush (Kolkwitzia)
Deutzias
Fothergilla
Forsythias
Honeysuckles (Lonicera)
Magnolias (most deciduous types)
Mahonias
Mockorange
Flowering quince (Chaenomeles)
Spireas (Spiraea)
Lilacs (Syringa)
Viburnums
Weigela

These shrubs form their flower buds in the summer. Pruning them in the fall removes some, if not, all flower buds. Tall unruly shrubs can be partially pruned back if they spoil the appearance of your home and grounds. Expect some loss of spring blooms. You can complete the task in late spring.

Remove dead and dying branches at any time. Channel all the plant’s energy to the strongest buds and prune out weak wood. Thin out crowded and crossing branches to open up the interior of the shrub to better sunlight penetration and air circulation. This also reduces fungal diseases such as powdery mildew common to lilacs and other shrubs. Some heavy scale and adelgid infestations can be pruned off.

If a shrub is in poor health, you may want to attempt “renewal pruning”. You may opt to cut back most of shrub, leaving a few strong water sprouts around the old shrub base. Root suckers below ground can also rejuvenate an old shrub.

Storing Vegetables Outdoors Over The Winter

Posted by Hugh on October 7th, 2014

Use covered cold frame for vegetable storage in winter

In early fall before killing frost arrives, harvest of fresh vegetables is central on gardeners’ minds. You might consider storing some (not all) vegetables outdoors to take advantage of frigid winter temperatures ahead. Limited refrigerator space in your kitchen is not taken up.

Some root vegetables- namely beets, carrots, rutabagas and parsnips- are long keepers. These vegetables store best when harvested near, but not past, their maturity. To maintain safe eating quality, veggies need to be stored within a narrow temperature range between 33 and 40° F.

Carefully gather root crops without bruising or cutting the edible portions. Use a sharp knife to pare away stems and leaves. Gently wash away most of the soil from roots. Cover in damp sand or blanket with a 6 inch layer of loose (not packing) tree leaves or organic mulch.

A second option is to build your own root storage bin in a shady area near the home. Pack the vegetables into a tub, wooden box, 5-gallon bucket, or a plastic storage box (punctured with drainage holes). Start by placing several inches of moist sand on the bottom of the container. Lay a single layer of root vegetables that are not touching one another on the sand. Cover them completely with sand.

If the box is deep enough, add another layer of veggies and sand layer until box or bin is nearly full. Finish covering with a layer of moist sand. Plan accordingly as a full container may likely be too heavy to lift. When you are preparing a meal, remove stored vegetables as needed over the fall and winter months.

If you live in a cool (not frigid) winter climate, overwinter cool crops (broccoli, cauliflower, kale, cabbages, head lettuce) in a cold frame. Cover the harvested crops with a 6-12 inch layer of loose straw or leaves. No part of the green vegetable tissue should be left exposed. If covered with the glass slash, place a cloth blanket over so the sun does not heat up the cold frame. Plan to consume all veggies before the cold frame is needed to start new vegetable and flower plants in late winter.

‘Summer Snowflake’ Viburnum

Posted by Hugh on September 18th, 2014

‘Summer Snowflake’ viburnum at UT Gardens in Knoxville, TN in mid-September

Autumn may be coming or has arrived, but spring-flowering ‘Summer Snowflake’, a selection of doublefile viburnum (Viburnum plicatum var. tomentosum) continues to bloom. Native to Japan, doublefile viburnums are in a league of their own. Summer Snowflake grows 15 to 18 feet tall and a narrow 6 to 9 feet width or roughly 2:1 height to width.

Floral clusters of layered white flowers rest on the horizontal branches. Days later, prominently veined green leaves begin to emerge. Blooming is showiest, at its best around the end of April (in east Tennessee), nearly a week after flowering dogwoods (Cornus florida) have finished. Single snowy white flowers measure the size of a quarter, and each flat cyme averages 4 inches across.

Summer Snowflake is uniquely different because its branching tends to be upright and its repeat blooming. The spring bloom cycle is very showy. Secondary flowering extends almost 3 seasons. Bright red berries follow in late summer and fall, and rusty red fall color completes the season. Leaves are prominently veined. Birds quickly devour the small crop of berries.

Summer Snowflake viburnum is at its best in full sun and in a rich loamy well-drained soil. It fares well in partial sun (4 hours minimum sunlight). Shrub exhibits good drought tolerance within 2 years after planting, but repeat blooming declines if summer is exceptionally dry. Disease and insect problems are generally minimal unless shrub becomes environmentally stressed.

Summer Snowflake may be grown as a large specimen shrub or group several together for an informal hedge or screen. It rarely needs pruning except to control shrub size and form.

Sparse fruit load on doublefile viburnum

Autumn/Winter Garden Dressup

Posted by Hugh on September 15th, 2014

Silvery artichoke at Dallas Arboretum

Ornamental cabbage & kale at Dallas Arboretum

It’s fall and many gardeners take leave of their garden until spring. Autumn is a great time to create new color schemes that will carry over into the winter garden. It’s just like spring all over again! Frost hardy flowering plants get their turn, such as pansies, violas, snapdragons, and diascias (USDA Hardiness zone 7), a recent addition to this list. Plant them in containers or in ground beds.

Tough winter foliage plants such as Swiss chard, giant red mustard, bull’s blood beets, artichoke, and ornamental cabbage or kale are great garden companions. Add fragrant evergreen herbs around a porch, deck or patio areas such as rosemary, lavender, sage and thyme.

Design with in fall/winter plants in containers or garden beds. A good container assortment contains various plant forms and leaf colors. Spiky narrow evergreen shrubs such as ‘Green Arrow’ Alaskan cedar (Chamaecyparis nootkatensis), ‘DeGroot Spire’ arborvitae (Thuja occidentalis), ‘Sky Pencil’ holly (Ilex crenata), or ‘Dee Runk’ boxwood (Buxus sempervirens) add height to a bed or container design.

Weeping and spreading evergreens make colorful “spillers” such as yellow needled ‘All Gold’ juniper (J. conferta ‘All Gold’), winter bronze-leaf Russian arborvitae (Microbiota decussata), or green needled Prostrata plum yew (Cephalotaxus harringtonia ‘Prostrata’).

To insure winter survival, blanket the soil with 2 to 3 inches of organic mulch for root insulation and to conserve soil moisture. Prune off dead blooms and unsightly foliage. Flowering annuals, particularly pansies and violas, benefit from bi-monthly feeding with 10-10-10 or equivalent fertilizer or monthly watering incorporating water-soluble Miracle-Gro™, Jack’s™, or Daniels™.

Fall Blooming ‘October Skies’ Aster

Posted by Hugh on September 12th, 2014

‘October Skies’ aster (Photo by Andrea Sessions, Sunlight Gardens, Inc., Andersonville, TN

From Maine to Texas, the aromatic asters (Symphyotrichum (Aster) oblongifolius) are great garden performers in the fall garden (USDA hardiness zones 5–8). The cultivar ‘October Skies’ is one of the best. Plants are covered with lavender blue flowers (up to 1 ¼ inches in diameter) from late September thru late October. Each flower displays a gold button center. Its grey-green foliage smells minty when crushed.

With a low mounding habit these compact asters grow to 18 – 24 inches in height and spread and rarely require pinching. It is shorter and bushier and bluer (flowers) than sister seedling ‘Raydon’s Favorite’. Plant is a vigorous grower with sturdy stems that stand up well when covered with blooms.

October Skies, along with other aromatic asters, excels in full sun. It prefers a moist well-drained, organically rich soil, but adapts to average dry sites. Spring-planted aromatic asters establish quickly and develop good heat and drought tolerance by mid-summer. Asters do benefit to mulching and feeding at planting and once a year in the spring. Asters attract numerous pollinators, particularly many species of butterflies. Deer usually turn their noses up on aromatic asters.

October Skies ranks as one of the easiest to-grow perennials. As a rule, aromatic asters are highly disease and pest resistant. Plants can be cut back in late fall after flowering.