March Tree of the Month-Arborvitae -

Do you want to know what’s the #1 reason I hear when I’m called for a landscape design consultation?

“I need to screen my ___”

Fill in the blank: Neighbors, roads, trash cans, parking lots, pools, hot tubs…the list goes on. Face it, we can control what we do in our yards, but not what our neighbors do. This also explains why Green Giant arborvitae, Thuja ‘Green Giant’, is one of the top-selling plants OF ALL TIME. (See top photo.)

Some arborvitaes, like these in O’Fallon, MO, don’t get as wide as Green Giant but still make a good screen or hedge. Try American Pillar, or Tall Guy if you have a narrow planting space.

Customers want FAST-growing screens, and since many neighborhood associations forbid fencing altogether or limit fence heights, fast-growing evergreens are the answer. HOWEVER, you have heard this from me before: Mother Nature always has a price. And the highly favored arborvitaes do have some drawbacks.

This *Thuja plicata* at the St. Louis Zoo has an elegant shape and stately size.

First of all, there are two main arborvitaes commonly found in the industry. Thuja plicata and Thuja occidentalis. The sizes in both can range from 1’ to 60’ and everything in between. RESEARCH is another term you hear repeatedly here. If you want to get those discount plants at the big box stores instead of a local nursery, you’d better make sure there is a real botanical name on that plant tag you can check out. Remember to look for a cultivar name in single quotes, or a trade name! Thuja ‘Green Giant’ is different from Thuja MR. BOWLING BALL-different in like 58’ different. February Shrub of the Month-Bowling Ball Arborvitae –

*Thuja* MR. BOWLING BALL is a dwarf, round cultivar of arborvitae.

Another thing to remember is that, as a general rule, a plant that grows 60’ high, like Green Giant or similar, is going to have a wide base to support that height. If you want to screen your neighbor’s driveway from your driveway and you only have a 2′-wide strip to plant in, that’s great…those little 3-gallon-sized Green Giants will fit perfectly, if you both want to park your cars on the street starting in 3 years because neither one of you is ever getting into the garage again. Green Giant can get up to 18’ wide. NO, you don’t want to keep shearing them back either-that defeats the purpose and destroys the beautiful, pyramidal shape. This worsens once the trees grow above your head and you can’t reach to shear them anymore without hiring a tree guy with a cherry-picker.

*These Green Giant arborvitaes are sheared to match the shape of the Climatron base at Missouri Botanical Garden.*

Then there are the cultural requirements. Rule #1: Plants need water. Plants need water not only on day one after planting, but regularly throughout their ENTIRE lives. The first year or two is critical for arborvitae. When it’s 110+ for three weeks straight in August without a drop of rain, you’re going to have to water no matter how much rain we got in APRIL.

The graceful, evergreen foliage of arborvitaes can be easily damaged by heavy snows and ice.

Other issues with arborvitae can be bagworms and snow damage. Bagworms can be easily hand-picked…unless they are 30’ high and out of reach. Spraying is not only anti-eco-friendly, but the timing has to be perfect! Only bagworms that are actively foraging can be effectively controlled with insecticide.

That being said, if you are adamant about getting a nice arborvitae screen going, full sun is preferred, but it will tolerate part shade with some sacrifice of density. Moist, but well-drained soil is essential. Arborvitaes like even, consistent watering, so water them in dry spells, but don’t let them sit in water. Do not let them go into winter dry. If we have a dry winter with no snow or rain, give them a drink during one of the frequent winter warm spells.

*Thuja occidentalis* ‘Smaragd’ in MBG’s Rock Garden is a compact arborvitae with good screening properties, but without the massive volume of Green Giant.

There are dozens of cultivars out there-RESEARCH to avoid disappointment on many levels.

What I love about this plant;

-It’s evergreen.

-Beautiful pyramidal shape.

-Good for screening or specimen plant.

-Unique cultivars are available in multiple sizes, shapes, and colors.

What’s not so great;

-Overused.

-Can overgrow an area quickly. If you want tall, but not so wide, try American Pillar arborvitae that grows 20’ high, but only 4’ wide, or for something shorter, Tall Guy arborvitae at 8-12’ high and 2-3’ wide. There is a new cultivar, Sting arborvitae, that reaches 20’, but only grows 12-18” wide.

-A favorite of bagworms. Other pests include leaf miner, mealybugs, scale, and spider mites.

-Leaf blight and canker are other issues that can afflict arbs.

-Can get snow damage from wet, heavy snows and ice.

-If one dies in a mature hedge, it’s hard to replace it with one the same size.

-Winterburn (when cold winds strip foliage of moisture and cause discoloration and dead tissue) is common in arborvitae; a sheltered site can help alleviate this problem. Some arborvitaes do get a bronzy “fall color” during cold temperatures. This is normal, and the plant will green back up with warmer temps.

These arborvitaes have a bronzy winter color that will green up in spring.

-Comments or questions? Email Garden-Lou at gardenloustl@gmail.com

Words and photos by Jo Batzer

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