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Tuesday - May 12, 2009

From: Arlington, MA
Region: Northeast
Topic: Seed and Plant Sources, Transplants
Title: Height of tree to block sun on deck in Arlington MA
Answered by: Barbara Medford


I am trying to figure out how tall a tree I should buy in order to make sure to block out the sun on my deck


Since this might require some mathematical work, at which Mr. Smarty Plants does not excel, we will have to point you at some information and let you take it from there.

First, the tree you buy and transplant into your yard is not going to be big enough to shade your deck this week, because you want to transplant a young tree that can hope to survive being transplanted. You will need to look at possible selections, find out what their estimated mature size, both in height and circumference of the foliage, will be and about how long it will take to get to that size. If you're going to live there 15 years, you'll probably have nice shade before you move. If you want shade for your birthday party in July, we suggest you investigate awnings. And, please, don't be taken in by the "shade in one year" ads or "fast-growing tree, instant shade." Any plant that grows too fast will have weak wood, not be long-lived and break down easily. And stick with trees native not only to North America, but to the area in which you live. They will be adapted to your climate, rainfall and soil, while the non-natives can either die because your weather is too harsh for them, or become invasive because it's too perfect for them.

Second, you are going to have to study the hardscape around your yard, and make sure the tree roots, as the tree matures, are not going to interfere with foundations, sidewalks, driveways, etc. That will also help determine how tall the tree needs to be, because you are going to have to plant your little tree far enough from the deck to keep deck and tree from damaging each other. Roots of trees generally extend at least as far out as the shadow of the canopy of the tree and sometimes twice that far.

And, finally, which way does your deck face? Do you want it shaded in the morning or the afternoon? That will also be a determinant on where or how far your tree is planted. The sunlight will be coming from a slightly different direction in the summer than it does in the winter, so that will require some adjustments. 

Now, because we don't know how much space you have, where paving, deck, and foundations will be in relation to the planned tree, we will have to let you do the calculations. We are going to go to our Recommended Species list,  click on Massachusetts on the map, and Narrow Your Search to trees. We will make a few suggestions, but it's up to you to follow up, investigate their prospective heights and canopy widths, and what size tree you can reasonably put in the ground this season. You can use the same search technique to see if there are other trees or even tall shrubs that you would rather use. Remember, these are just examples - there are many other trees native to Massachusetts that you could choose.

Trees for Massachusetts

Carpinus caroliniana (American hornbeam) - 35 to 50 ft. tall, deciduous, medium water use

Cercis canadensis (eastern redbud) - 15 to 30 ft., deciduous, blooms pink March to May, low water use

Ilex opaca (American holly) - 25 to 60 ft., evergreen, blooms white, green March to June, medium water use

Liriodendron tulipifera (tuliptree) - to 150 ft. tall, deciduous, medium water use

Carpinus caroliniana

Cercis canadensis

Ilex opaca

Liriodendron tulipifera





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