3-way spring check up nets well-shaped arborvitaes

Need help with your arbs? Thank C.C. for emailing to us:

We have two trees or bushes on the side of our garage.  We have been told they are cedar.  They are 10 to 15 feet tall and are in desperate need of pruning but we have no idea what we are doing.   Can you give me some direction? - C.C. -

Late winter is a good time to prune arborvitaes, to catch them before they begin growing, remove some tips and thereby "reprogram" remaining branches' pecking order. The result is that limbs further in and down will do more growing than they would have otherwise.

Here's a picture of one of the two trees C.C. would like to prune. It's an arborvitae (Thuja occidentalis), also known as white cedar, eastern cedar or eastern arb.

Here's a picture of one of the two trees C.C. would like to prune. It's an arborvitae (Thuja occidentalis), also known as white cedar, eastern cedar or eastern arb.

C.C.'s brief question led us down several side tracks. The simple answer is here, but please do look also at Arb cut in timeArbs cut hard and Arbs long recovery. The photos in those other articles can help you decide how far to cut, anticipate the rebound, and then keep these trees from getting out of hand again.

Three checks on arborvitaes each spring

These are plants that can reach a point of no return. Keep an eye on their size, uniformity of greenery, and density.

First check: Size

Notice if your arbs have reached the maximum height or width you can allow.

Yes? They have just reached their limit? Cut them! See Arb cut in time.

In cases like C.C.'s, the trees are too big already. The check becomes, how big do you want the trees to be and will they tolerate being cut back that far?

For instance: If you want an arborvitae to be 3 feet shorter and 2 feet narrower, now's the time to look inside. See how deep the greenery extends inward. If there's green within the outline you imagine -- lacy green branches or green buds -- then you're good to go. You can cut back.

Chop that plant back to the line you drew. Then cut back further on any branch that's wood-only. Don't leave any woody stubs . Cut everything back to a leafy bud or to a side branch that has leaves at its tip.

Then wait for the tree to grow back. For what it will look like in the interim and an idea how long the regrowth will take, we give you Arbs cut hard and Arbs long recovery.

If this is your first spring of checking your arbs, start by deciding how big you'd like the plant to be. The dashed orange line might be the objective here.

If this is your first spring of checking your arbs, start by deciding how big you'd like the plant to be. The dashed orange line might be the objective here.

Next, see how far greenery goes into the arb's interior. The arb that yielded this branch could be reduced by 24 inches  -- to the dashed orange line. That would take two cuts (the orange arrows). Alternatively, it could be cut back to a size indicated by the blue dashed line. That would take one cut (at the blue arrow).

Next, see how far greenery goes into the arb's interior. The arb that yielded this branch could be reduced by 24 inches -- to the dashed orange line. That would take two cuts (the orange arrows). Alternatively, it could be cut back to a size indicated by the blue dashed line. That would take one cut (at the blue arrow).

Arbs in spring, check #2: Uniformity of foliage

Is one side or the lower half becoming thin?

Arbs are sun lovers that we often relegate to shady places. They lose density, especially on the north side and where their own top billows out wider than their feet. Thin areas can reach a point of no return -- all the greenery languishes and falls from those branches and cannot be regrown. Don't let that happen.

When you see thin places in an arb, thin the top or the opposite side or prune overhanging trees. The objective is to let more light reach down or through to the thin area.

 Hi arbs, say "Cheese!"

We don't trust our memory for spring check. We take photos as a regular part of garden care, and review them each year.

Here's an arb hedge that had grown to touch the wires above, and to lap onto the driveway. We cut it back. That left holes

Here's an arb hedge that had grown to touch the wires above, and to lap onto the driveway. We cut it back. That left holes

Here's that hedge 24 months later. Our assessment and patience are being rewarded -- the shrubs were indeed healthy enough to recoup. This year we'll cut it again, shortening and narrowing the top and pushing the sides back off the rail fence.

Here's that hedge 24 months later. Our assessment and patience are being rewarded -- the shrubs were indeed healthy enough to recoup. This year we'll cut it again, shortening and narrowing the top and pushing the sides back off the rail fence.

An arb hedge four years ago.

An arb hedge four years ago.

The same hedge today. The top's been allowed to become too dense and the lower branches are losing density. If the only cutting that's done is to shear the top, this is bound to happen. The top and shoulders of this hedge need thinning right away. Read on, about thinning

The same hedge today. The top's been allowed to become too dense and the lower branches are losing density. If the only cutting that's done is to shear the top, this is bound to happen. The top and shoulders of this hedge need thinning right away. Read on, about thinning

Arbs in spring, check #3: Interior density

Is the plant becoming hollow? If so, cut back every 4th or 5th branch to let light reach remaining interior leaves and buds. If you don't begin doing this regularly, you can kiss that plant good bye. When a plant has a lot of wood (starch users) and relatively little leaf (starch producers), it begins to starve. Weakened, it falls prey to its insect pests, diseases, and has less tolerance for marginal growing conditions. As it loses ground to these problems, it thins even more.

See light shining through these arbs? The trunk and main branches are visible as through thin curtains. The plants have become a thin green skin over emptiness. This happens when plants are sheared repeatedly and never thinned.

See light shining through these arbs? The trunk and main branches are visible as through thin curtains. The plants have become a thin green skin over emptiness. This happens when plants are sheared repeatedly and never thinned.

Will thinning cuts leave gaps? Yes. That's the point, to create windows so light can reach the interior. However, when a plant is thinned regularly there is always green coming from deeper than the cut. You will not see gaping holes, only clefts into more green -- spaces that fill rapidly.

Will thinning cuts leave gaps? Yes. That's the point, to create windows so light can reach the interior. However, when a plant is thinned regularly there is always green coming from deeper than the cut. You will not see gaping holes, only clefts into more green -- spaces that fill rapidly.

This is a branch from the upper "shoulder" of the hedge you saw previously. To thin this branch, cut at the three orange arrows to shorten the branch and leave the circled greenery.

This is a branch from the upper "shoulder" of the hedge you saw previously. To thin this branch, cut at the three orange arrows to shorten the branch and leave the circled greenery.