Planting a Hemlock Tree: Pros, Cons and Root Depth

Which hemlock are we talking about

This article is about the hemlock trees in the genus Tsuga, mainly Eastern hemlock (Tsuga canadensis, also sold as Canadian hemlock), plus related species such as Carolina hemlock and western hemlock. They are evergreen conifers with soft, flat needles and small cones. If you are not sure how conifers differ from other trees, our guide to deciduous vs coniferous trees covers the basics.

They are unrelated to poison hemlock (Conium maculatum), a toxic herbaceous weed in the carrot family. The tree is not the plant behind the famous poisonings, despite the shared name.

Pros and cons of a hemlock tree

Pros

Tolerates shade better than most evergreens, so it can work where pines and many other conifers struggle.
Soft, fine-textured, dark green foliage with a graceful look.
Can be grown as a screen or, with regular shearing, as a formal hedge. See fast-growing trees for a privacy screen to compare.
Can be used as a screen, though note that deer browse hemlock, especially in winter, so young trees may need protection.

Cons

Pest vulnerability: in much of the eastern United States, hemlock woolly adelgid has killed or weakened many Eastern and Carolina hemlocks.
Dislikes heat, drought, wind, and soil that stays soggy.
Shallow roots, which can be damaged by digging, compaction, or drying out. See planting under trees before adding a bed beneath one.
Relatively slow growth, so a screen takes patience.
Needs more attention to watering in its first years than many tougher landscape trees.

How deep do hemlock roots go

Hemlock roots are generally described as shallow and spreading rather than deep. Most of the root system sits in the upper layers of soil and can extend outward well beyond the branch tips as the tree matures. There is no single reliable depth figure, because it varies with soil and site.

What this means in practice:

Avoid trenching, grading, or paving close to the trunk.
Mulch to protect the roots and hold moisture.
Water during dry spells, since shallow roots dry out faster than deep ones.
Give a mature tree room, and check how far it will be from a building before planting.

How fast does a hemlock grow

Eastern hemlock is usually described as slow to medium in growth, and it often starts slowly after planting while it establishes. Growth depends strongly on light, moisture, and soil. A nursery tree in a good site may add roughly a foot or less per year in its early years. It can reach a large size and live a very long time in natural forests, but a landscape tree should not be expected to match that quickly.

Where to plant

Light: Part shade or dappled light is a good choice. Hemlocks tolerate full shade, but avoid hot, exposed sites with strong afternoon sun, and avoid windy spots where needles can dry out in winter.
Soil: Moist but well-drained, slightly acidic soil rich in organic matter is ideal. Heavy, waterlogged clay and very dry sandy soil are both poor choices.
Spacing: For a screen, many sources suggest roughly 10 to 15 feet between full-sized trees, and closer, around 4 to 6 feet, for a formal hedge that you plan to shear. Check the mature size on your plant’s tag.
Neighbors: Keep away from other trees that compete heavily for water in the same shallow root zone.

When to plant

Early spring and early fall are generally the best windows, because temperatures are mild and the tree has time to root before extremes. Avoid planting in the heat of summer or when the ground is frozen.

How to plant a hemlock step by step

Check the tree. Choose a plant with healthy, evenly green foliage. Ask the nursery whether it has been checked for woolly adelgid, and look for small white cottony tufts at the base of the needles on the underside of twigs.
Dig a wide, shallow hole. Make it about two to three times as wide as the root ball and no deeper than the root ball itself.
Set the tree slightly high. The top of the root ball should sit at or slightly above the surrounding soil so it does not settle too deep.
Remove wrapping. Take off string, wire, and any synthetic burlap; cut away natural burlap from the top of the ball.
Backfill with the native soil. Amend lightly if needed, but avoid creating a rich pocket that discourages roots from spreading out.
Water thoroughly to settle the soil and remove air pockets.
Mulch two to three inches deep, keeping it a few inches back from the trunk.

Aftercare

Water deeply and regularly during the first couple of growing seasons, especially in dry weather. Soil should be moist, not saturated.
Keep mulch topped up.
Prune lightly if you want to shape it. Avoid cutting back into bare wood, since conifers often do not regrow from old wood.
Wait to fertilize until the tree is established, and follow a soil test if you can.

Common problems

Hemlock woolly adelgid: tiny insects that feed at the base of needles and appear as white woolly tufts. Signs include thinning foliage and needle drop. Treatment options exist, but they are best discussed with a certified arborist or your local extension service.
Spider mites and scale: can cause stippled, dull, or yellowing needles, particularly in hot, dry sites.
Drought and heat stress: browning or dropping needles, more common on exposed sites.
Winter burn: browning from drying wind and sun in cold weather.

If you are choosing among shade-tolerant evergreens and are worried about adelgid in your region, ask a local nursery or extension office which trees do well there.