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

Pruning An Old Nandina

Posted by Hugh on January 5th, 2010

Nandina (Nandina domestica) is often mis-pruned. By shearing or topping nandina foliage, blooms and resulting berries are lost (see photo). The plant eventually becomes leggy and thin.

Sharply prune back about a third of the taller stems at the base of the shrub in March before spring growth begins. Stagger the cuts 3 to 6 inches above the soil. Within a few months new shoots begin to grow out near the soil line, eventually filling in around the shrub base. The regrowth gives the nandina a fresh appearance.

Why My Tree Or Shrub Doesn’t Bloom

Posted by Hugh on January 5th, 2010

Frustrated by a fruit tree or ornamental tree that does not bloom? There are 5 primary causes:

Lack of sunlight – insufficient light reduces flower bud development
Fertility – too much nitrogen fed to plants can over-stimulate vegetative growth, either delaying or preventing flower bud development
Winter injury or chilling tender flower buds in one or more spring frost
Pruning at the wrong time of year, essentially removing all flowering wood
Alternative (biennial) flowering when a plant bears too much fruit and will not initiate new flower bud for the next year

All these factors are inter-related. While bad pruning practices may reduce flower bud numbers, good timely pruning practices increase blooming. Usually, an unpruned tree or shrub does not bloom heavily. A shrub or tree with an open branch canopy in full sun will flower reliably every year.

Prune spring flowering shrubs and trees immediately after flowering. These plants set flower buds on woody growth produced in the summer. Summer-flowering plants set their flower buds on spring wood in the same year when they bloom. They can be pruned in late summer or wait until late winter and early spring.

Big Begonias

Posted by Hugh on January 4th, 2010

The Benary ‘Big Begonia’ series are a hit, “begonias on steroids”, some gardeners may say. Individual flowers are twice that of other bedding begonias. Colors are vivid with three cultivars currently available . ‘Big Rose Bronze Leaf’ is my personal favorite. (pictured)

Begonias grow best in well drained, humus-rich garden soil. Provide tender -loving care for the first 4 weeks in the spring, and plants will bloom non-stop through a long hot, dry summers into the first hard frost autumn.

Plant the Big begonias in full sun or partial sun (a minimum of 5 hours of sun recommended). Disease and insect pests are rarely an issue for these tough, non-stop flowering annuals. Do not plant begonias in the same garden spot more than 3 consecutive years to avoid buildup of soil pathogens.

Angelonia in the Summer Garden

Posted by Hugh on January 4th, 2010

Tired of marigolds and petunias? Angelonias (A. angustifolia) are superior summer garden annuals. Angelonias require very little care. They possess superior heat and drought tolerance.

I prefer the Serena series (seed produced type) because local greenhouse growers produce and sell them more cheaply. Vegetative (cutting) type angelonias grow taller, are heavy bloomers, and are more pricey at garden centers.

Varieties of ‘Serena’ angelonia come in white, pink lavender, lavender, and purple flowers. Plant them after the danger of spring frosts in your gardening area is low. After planting, follow-up with a few early waterings. Then, sit back and enjoy angelonas in constant bloom from late spring to the first hard frost of autumn.

Serena angelonias grow 12-15 inches in height and 14-16 inches in spread in my zone 6-b garden.

photo: pentas (front) and ‘Lavender Pink Serena’ angelonia (rear)

Root Injury to Container Plants

Posted by Hugh on January 2nd, 2010

The 4 most common reasons why gardeners lose outdoor container plants during the winters are:
1. Sub-freezing temps
2. Soil freezing for long periods
3. Waterlogged roots
4. Dessication from dry winter winds

Roots are not as cold hardy as above-ground shoots, trunks, branches, etc. Evergreen plants become more challenged when the soil media is frozen. Their leaves demand more water and nutrients that the roots are not able to supply from the frozen ground.

Root injury for most woody tree species begins at 22°F. This is soil that has little water in it. Keep in mind that water freezes at 32°F. So, one tip is to keep container plants watered, but not waterlogged. Most plants are injured when soil temps hit 16°F over a 24-hour period.

Pots must provide adequate drainage. Planting in a soil-less media containing high percentages of an organic component such as peat moss and/or compost, plus a gritty substance as coarse sand, tiny pea gravel or perlite for aeration and drainage. The pot should include bottom holes to weep out excess moisture.

Evergreens naturally shed most rain and snow like an umbrella and supplemental watering is critical for these plant compared to deciduous plants. Irrigate containers at least twice monthly, assuming that natural rain and snowfall will supply the rest.

Coral Bark Maple Blazes in the Winter Landscape

Posted by Hugh on January 1st, 2010

Sango kaku Japanese maple (Acer palmatum ‘Sango kaku’) has light green summer foliage on a fairly upright branches. In the fall, foliage turns yellow-gold with some light tints of red, otherwise a very ordinary tree. It’s in the fall and winter seasons when this 20-25 foot ornate maple excels. The green branches and twigs turn bright coral red, aglow in the winter sun. Sango kaku makes a beautiful addition to any landscape in USDA zones 6-7.

Sango kaku prefers 1/2 day of sun, preferably in the morning and early afternoon hours. New spring growth is thin and rank, the tree needing pruning annually to maintain a good tree form. A colder than normal winter often results in twig dieback, requiring minor cleanup pruning cuts in the spring.

‘Beni kawa’ is another Japanese maple with exquisite salmon colored bark beginning in late fall-winter. It appears to possess better cold and heat tolerance. Tree height is alot smaller, perhaps only 10-12 feet tall at maturity. Growth on Beni kawa is not as spindly and less prone to winter twig dieback. Beni kawa leafs out 2 weeks later than Sango kaku, avoiding spring freeze injury.

Princess Lilies — Hardy in Zone 6

Posted by Hugh on December 29th, 2009

Not all alstroemerias are alike. I have been enjoying my Princess lilies (alstroemeria hybrids from Holland) over the past 6 years. They have been surprisingly winter hardy in zone 6-b where I garden. Further south in zones 7 and 8, Princess lilies prefer part sun to partial shade.

I grow’em on the east side of the garden in full sun. The harsh afternoon sun of summer is filtered through the tall shrubs and trees nearby. Mulching the soil provides extra freeze protection to roots in the winter and guarantees their return next spring.

Princess lilies need little care after planting. I feed’em a handful of granular 10-10-10 around each plant in late winter. Give them a weekly irrigation for 1/2 hour or more during summer dry spells. Plants grow short and compact and are also suitable for containers on the deck or patio.

Currently, there are 17 varieties, richly colored in whites, yellows, pinks and reds. This spring I will be adding 1 or 2 new Princess lilies to the perennial flower border .

‘Sky Pencil Holly vs ‘Dee Runk’ Boxwood

Posted by Hugh on December 28th, 2009

‘Sky Pencil’ holly at Saunders Brothers Nursery in Virginia

‘Dee Runk’ boxwood

Boxwoods and hollies are mainline evergreen shrubs, utilized for low hedging, privacy barriers. Single shrubs are planted solely for their architectural accent. Both hollies and boxwoods grow best in moist, well-drained soils and in full sun to partial shade. Both prefer soils with a pH of slightly acidic to slightly alkaline. Boxwoods tend to be more shade tolerant than Japanese hollies. In winter plant foliage may scorch or bronze if grown in open sun.

Plants are generally tolerant of pruning and shearing. Pruning too early in spring may promote tender new growth that is easily injured or killed by a late spring frost.

There are few shrubs that fit into narrow spaces better than ‘Dee Runk’ boxwood (Buxus sempervirens ‘Dee Runk’). Research has shown that Dee Runk is a better choice than currently popular cultivar ‘Graham Blandy’, which is seriously troubled by soil borne diseases, specifically Phytophthora root rot.

‘Sky Pencil’ Japanese holly (Ilex crenata ‘Sky Pencil’) exhibits a similar upright (fastigiate) form. They are finicky regarding soil drainage. Plants are particularly susceptible to soil root rot diseases including Phytophthora and Pythium.

Both ‘Dee Runk’ boxwood and ‘Sky Pencil’ holly grow well in large landscape containers on patios and along downtown streets in USDA zones 6-9. Expect mature shrub heights between 8-10 feet.

Planting Leyland Cypress May Be Big Mistake

Posted by Hugh on December 23rd, 2009

If you live in USDA Plant Zone 6-b – 7, planting leyland cypress (x Cupressocyparis leylandii) could eventually turn into a maintenance diseaster in your landscape. Leyland cypress is a green behemoth, too fast and aggressive for most folks to handle. Ask yourself, “do you really need a 60-70 foot evergreen privacy screen around your property?” If neighbors can’t view in, you can’t see out.

Many gardeners make the mistake of planting leyland cypress only 6-8 foot apart. Leyland demands a wider 16-18 foot spacing. Unfortunately, leyland is also susceptible to 3 fungal needle blight diseases. Diseases usually don’t infect until shrubs are 10 years and older. There are no practical cures (pesticides) for these diseases. Over time the shrubs may need to be removed at a considerable cost to you.

If you must grow tall screens or hedges, I recommend the more dependable Japanese cedar (Cryptomeria japonica) or Green Giant arborvitae (Thuja x plicata). In the 20-25 foot height category, plant Nellie R. Stevens holly, Foster#2 holly and Emerald arborvitae (Thuja occidentalis ‘Smaragd’).

Some great evergreen choices in the 10-15 foot range are leatherleaf viburnum (Viburnum rhytidophyllum), skip laurel (Prunus laurocerasus ‘Schipkaensis’) and ‘Hick’s Yew (Taxus x media ‘Hicksii’).

Beware of Storm Damaged Trees

Posted by Hugh on December 20th, 2009

This past weekend Northeast Tennessee as well as most of the coastal eastern U.S. was hit by heavy snow, 7 inches and more of heavy, wet clinging snow. Many of my neighbors lost electric power, telephone and cable.
A driveby survey of tree damage around the neighborhood found that the following tree species suffered the most breakage (in order of severity):

Chinese (Siberian) elm
Silver maple
White pine
Weeping cherry (pictured)
Topped trees
Bradford (callery) pear
Red maple
Dead or dying trees
Sycamore (London planetree)
Southern magnolia
Sweetbay magnolia
Yoshino cherry
Dogwood

The type of injury ranged from large falling limbs two inches or more in diameter (Chinese elm, white pine, and silver and red maples) to many small branches less than one inch diameter (weeping cherry. magnolias and dogwoods).

Lessons learned:

Select a tree species that is reliably storm resistant. Expect some limb breakage on any tree species, but fast growing trees like Chinese elms and silver and red maples, and those that are not properly maintained, suffer the most damage. When homeowners properly prune landscape trees every 5 years, storm damage is considerably less.
Old mature trees, which have outlived their expected life span, should be removed and replanted with younger specimens. For example, Chinese elm, silver maple and white pine reach full maturity within 40 years. Bradford pear has a short replacement time of 15 years. Pruning maintenance on all landscape trees should be every 5-7 years.
Topped trees suffered considerable limb losses as the weakened re-growth is exceptionally susceptible to breakage. The topping of trees is never a recommended practice. In my opinion, if a large tree threatens your home, personal property or utility lines, either seek care advice from a professional arborist or have the tree removed by a licensed and bonded arborist.
Previously dead or dying trees pose a bigger hazard during in a storm.