TREES ON TERRACES
You want to put some deciduous trees in your rooftop garden - What do you choose? The answer of course depends on many things. Here are some parameters you should use as a guide.
What is your overall wish list
You need to decide on what you want – basically answer the “what is important to you” question. Make sure to note where you are flexible in your criteria.
- Flowers - Only in spring, or summer, or both, no flowers, colorful stems
- Spread - A compact tree, or spreading for a chair to go under
- Size - Big, small, wide, narrow, for a corner
- Grouping - Stand alone, a focal point, a grouping, the same type, or different
Conditions in the garden
These 5 conditions will point you to a list of trees you could use while eliminating many that won’t work there based on your criteria.
- Light - Sunny all day, partial sun (morning or afternoon),
- Wind - Strong and relentless, no wind
- Space - Small space size, plenty of room to spread out
- Hazards - Exhaust vent, reflection from glass wall, overhand from above
- Cold - High exposure to cold, protected spot against building
Which trees do best in which conditions
To determine which do well in those conditions available – you need to know your plants!Plant selection for the conditions requires you understand what the tree is all about. Read about each tree you are considering.You don’t need to become a botanist – just learn enough to make a better choice.
What are their particular needs or characteristics of the species
Is the blooming messy, can fruit stain furniture, do they bloom at all, how big do they get -Need big pots.
What are their most common liabilities
Which insect or disease do they get. To show you an example of this criteria analysis here are a few of the trees we use often on rooftops and how their characteristics break down.
Acer palmatum “Sango Kaku” (Coral Bark Maple)
PARTIAL SUN TO SHADE (4,000-1,000 fc)
pH 7.0 - 7.0
One light prune in Spring after blooming to remove winter damage, one heavy prune in Fall to keep shape.
NON TOXIC
Easy to grow and very winter hardy. Has spectacular red stems and branches when young. Stems loose the red color as they age.
PREFERS COOL Subject to heat stress, heat reflecting from surfaces and heat vents. Avoid having the hot summer afternoon sun falling on containers which will overheat and stress the roots.
Flowers are inconspicuous and not fragrant.
Can get Aphids, scale, Anthracnose Disease,
From Japan, Korea, China (P Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : North or east facing terrace, or against a west wall, in partial shade
Amelanchier Canadensis (Shadblow)
SUN (8,000-4000 fc)
pH 5.5 - 7.5
White, light pink, and dark pink flowers
TOLERATES SEASONAL CHANGES
NON TOXIC
A good choice for a small plot, this handsome tree is more compact in size and works hard for its place in the garden by putting on shows of blossom, fruit and autumn leaf color. Usually grown as a multi-stemmed specimen, it enjoys a sunny or partially shaded spot in moist soil. White blooms decorate the branches in early spring and are followed later in the season by purple fruits. Birds will eat these immediately. In early autumn, the dark green leaves turn vivid shades of gold before falling.
Caution: Genus prone to get Cedar Apple Rust
Native from Nova Scotia to Alabama (Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : Anywhere you want in Sun
Betula nigra (River Birch)
SUN (8,000-4000 fc)
pH 5.0 - 6.0
TOLERATES SEASONAL CHANGES.
Soil should be WET at all times.
NON TOXIC
One heavy prune in Summer to keep shape, one light prune in Fall to keep shape. DO NOT PRUNE IN WINTER OR EARLY SPRING OR IT WILL BLEED.
Native to Eastern US, extremely winter cold hardy and summer heat tolerant once established. Will recover fully if dried out. Likes acid soil. Their light green foliage turns yellow in fall. Losing their leaves for winter shows off their colorful, peeling bark, thin graceful branches, and hanging cone-like fruit. Young trees have dark-colored bark until their trunks reach 1 inch around.
Likes a large soil volume or its’ growth gets stunted. Benefits from soil replacement in Spring and Fall to stimulate new root growth.
Can get Birch Leaf Miner, Green Aphids, Spiny WH Gall Aphid, Webworm, Soil Grubs, Webworm
Native to Eastern US (Sunny, Wet Soil, S Rain, Cool, Calm)
PLACE IN : Anywhere you want in Sun
Cercis Canadensis (Redbud or Forest Pansy)
PARTIAL SUN (4,000-2,000 fc)
pH 6.5 - 7.0
Pink flowers in spring, white also available
PREFERS COOL. Established plants tolerate summer heat.
DOES NOT LIKE HIGH EXPOSURE LOCATIONS.
One light prune in early Summer after blooming.
NON TOXIC
Spring brings a profusion of white, pink or red flower clusters that bloom as the leaves unfold or just before. Red-brown, flat seedpods that follow in summer last through winter. Broad, heart-shaped leaves turn yellow in autumn.
Has a branching habit that may lead to undesirable ""V"" shaped stems. Prune to remove these and promote more side stems as these ""V"" shaped branches are subject to splitting."
Can get Green Aphid, Cottony Cushion Scale, Bacterial Spotting
Native to Eastern US (P Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : Against a building or wall facing North or East in a protected non windy spot.
Cornus Kousa (Japanese Dogwood)
PARTIAL SUN (4,000-2,000 fc)
pH 4.5 - 5.0
White flowers in late Spring
PREFERS COOL
Prune sparingly in Spring, after blooming, remove suckers
Caution: sap may cause Dermatitis: The sap or thorns may cause a skin rash or irritation.
Tolerates shade but not wet soil. Shallow rooter, so mulch heavily in summer to keep those roots cool.
Very prone to all types of environmental stresses, heat, cold, wind, too much or too little water, insects, and funguses.
Can get Green Aphid, Oyster Scale, Cottony Cushion Scale, Anthracnose disease
Native to East Asia (P Sun, Wet Soil, Rainy, Cool, Calm)
Warning : Fruit will drop when ripe and stain floors, sofas and cushions. Remove when green once they form.
PLACE IN : North or east facing terrace, or against a west wall in partial sun
Lagerstroemia speciose (Crepe Myrtle)
FULL SUN (8,000-4000 fc)
pH 6.0 - 7.5
Blooms in Summer, flowers are pink, lavender or white.
Prefers one heavy prune in early Summer after blooming.
NON TOXIC.
Tolerates exposure well.
These small, multi-branched shrubs to small single-trunked trees are known for their ornamental flowers, bark and foliage. The large showy clusters of flowers range from white to pink to red to purple. The upright-arching trunks have gray to brown bark, which peels away to reveal the smooth pale-pink inner bark.
Can get Green Aphid, Grasshoppers, Japanese Beetles
From Southern Asia (Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : Anywhere you want in Sun
Prunus cerasifera (Ornamental Plum)
SUN (8,000-4000 fc)
pH 6.5 - 7.5
Light Pink flowers in spring
TOLERATES SEASONAL CHANGES
Prune ONCE only in the Spring immediately after blooming.
Caution : Seed ingestion may cause serious gastrointestinal illness.
Deciduous tree to 20' with a shrubby and twiggy habit. Needs evenly moist soil with good drainage.
Very winter hardy.
Highly prone to scale insects and fungal rusts. Brown Armored Scale Insects, Soil Grubs, oyster scale, wax scale
From Europe to Asia (Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : Anywhere you want in Sun
Stewartia pseudocamellia (Korean Stewartia)
PARTIAL SUN (4,000-2,000 fc)
pH 6.0 - 7.0
White Camellia like flowers in Spring
TOLERATES SEASONAL CHANGES.
NON TOXIC
Shade from hot afternoon sun – good for an East facing terrace.
Can get Wax Scale.
These are distinctive trees and shrubs in every season. Their leaves become rich green in spring, and their camellia-like flowers bloom in summer. In autumn their leaves blaze with color. Flaking brownish bark reveals lighter inner bark, so mottled trunks are a mix of orange, gray and reddish-brown. Prefer loamy acid soil.
Transplant only when young. Mulch to keep soil moist.
From Japan (P Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : North or east facing terrace, or against a west wall
Styrax japonicum (Japanese Snowbell)
PARTIAL SUN to FULL SUN (4,000-2,000 fc)
pH 6.0 - 7.0
Prune in summer immediately after blooming. Late season pruning may affect next years flower count.
TOLERATES SEASONAL CHANGES.
NON TOXIC
Tolerates windy spot.
A wonderful tree as a focal point or specimen. Appropriate for smaller yards as it is slow growing. The Japanese snowbell is covered with white fragrant blossoms in June or July. It has a lovely shape and a gracefully spreading habit which might make it difficult to use on terraces or tight spaces. The Japanese snowbell is reliable and easy to grow.
Saplings may need staking for the first year or 2 while trunk develops.
Flowers can be messy in Spring.
China, Japan (P Sun, Wet Soil, Rainy, Cool, Calm)
PLACE IN : Anywhere you want in Sun
At Plant Specialists we love trees !
ALL OF THEM!!!
Call us - let us put some in your garden !
PLANT SPECIALISTSGREENING NEW YORK FOR OVER 53 YEARS !
Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBAAll photographs used with permission @SHUTTERSTOCK