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Planting & Caring for Garry Oak Trees

Garry oak bark (photo by Emrys Miller / Rocketday Arts)

Garry oak bark from Summit Park (photo by Emrys Miller)

The majestic Garry oak is under threat from urban development and encroaching trees, shrubs and the climbing vines of English Ivy. You can help reverse its decline while adding beauty to your property. The trees can live for hundreds of years. Growing and caring for a Garry oak tree is a project that you can do with your children to create a lasting legacy for your family. Plant acorns or seedlings and watch them grow.

From Acorns to Oaks

The Float Test

Put your acorns in the bottom of a container such as a large pail or bathtub, and fill it with water. Throw away the acorns that float to the surface or sit on the bottom making bubbles. The rest of the acorns on the bottom are healthy: they should not have any holes or cracks. To get the cream of the crop, choose the ones with the fewest flaws or blemishes. Soak these for 24 hours and then plant them.

  • The best time to collect acorns is in the fall, as soon as they start falling from the trees. Collect several so that that you have a good selection of healthy ones.
  • Use the acorns quickly; they germinate best soon after falling from the tree.
  • To choose the healthiest acorns, use the float test (see box). If you find an acorn that has already sprouted (you will see an emerging white root), plant it immediately, on its side, following the instructions below:
    • Plant your acorns in late fall–early winter, choosing an open, sunny site
    • Moisten the upper layer of soil at your planting site
    • Plant acorns 5–10 cm (2–4") deep, on their sides
    • When the seedling appears, surround it with wire mesh to protect it from wildlife and human activity
  • During the first two summers, water the seedling every 2–3 weeks
  • Clear away grass and weeds in a 1m (3’) circle around the seedling, until the seedling is at least 15–25 cm (6–8") tall. Use mulch around the tree as a weed barrier, but keep it away from the stem
  • If you want to store acorns temporarily, bury them in leaf piles rather than in pots, and transplant the sprouted acorns or seedlings while they are still young and have short roots

Transplanting Garry oak Seedlings

illustration by Dave McPhie

Illustration by Dave McPhie, adapted from a drawing by Pierre D'estrube

One method of transplanting Garry oaks is to use the ‘sand and snorkel’ technique.

  • After digging a large hole, place about 3 cm (1") of coarse sand in the bottom. Place the root ball in the ground.
  • Stand a sand-filled tube of permeable material (e.g., landscaping fabric or a nylon stocking) along one side of the hole, as shown in the diagram.
  • Then place 10 cm (3–4") of soil in the hole, followed by 3 cm (1") of coarse sand, and continue layering in this way until the hole is full.
  • Tamp the soil down, and water thoroughly. The vertical and horizontal corridors of sand will draw water to several root levels.
From Acorns to Oaks

An acorn is the fruit of an oak tree. There is a nut containing a single embryo protected by a tough shell that hangs from a branch by a “cupule” or stemmed cap.

  • Water regularly for the first few years until the seedling is established.
  • You may also want to provide the tree with protection from birds and deer.

Caring for Garry Oak Trees

  • Protect your tree from soil compaction in its root zone, as well as from stress or damage from parked cars, swimming pools or construction projects
  • Don’t pave under the tree. Tree roots extend out at least as far as the branches of the tree and the ground beneath the canopy should be protected from disturbance
  • The older the tree, the more important its shallow roots are and the less able it is to adapt to change
  • Avoid sudden changes such as over-watering or long periods without watering
  • Don’t create stress by hanging things off the tree such as signs or clothes lines
  • If you have a stand of oaks on your property, you may need to find out about techniques to maintain the trees’ health, such as thinning and reduction pruning to thin the canopy. Consult an arborist for advice.
  • Protect your trees from invasive vines such as English ivy that can smother and kill. For information on ivy removal, see our invasive species manual.

Oak Pests and Diseases

Garry oak trees have evolved with hundreds of different insect species, as well as a number of micro-organisms, and it’s perfectly natural to see nibbled oak leaves or leaves with small holes in them. Large spherical galls (1–2 cm, ½–1" “speckled oak leaf galls”) are caused by native gall wasps whose populations are kept in check by native parasitoids and do not pose a serious threat to Garry oak trees.

Introduced insect pests such as jumping gall wasps, oak leaf phylloxeran, winter moths and gypsy moths, along with the fungus-like organism that causes sudden oak death can be more problematic than native insects:

  • Jumping gall wasp: The jumping gall wasp lays its eggs on several ornamental oak species in British Columbia, but the Garry oak is the only tree species on which it can complete its life cycle and where it does the most damage. Tiny (1.5 mm, 1/16") yellow galls that look like mustard seeds on the undersides of the leaves house the wasp larvae. When the larva matures, the gall falls to the ground, and as the wasp moves around inside, the gall visibly and audibly “jumps”. Yellow-brown spots are left where the galls were attached to the leaves.

    Symptoms appear in mid-June and include anything from simple spotting of leaves on lightly infested trees to complete scorching and premature defoliation on the most severely infested trees. Fortunately, there are some parasitoids that feed on and kill the gall wasp larva, and earwigs and some ground beetles eat galls. Although there are commercially-available insecticides, these are not recommended. For more information and photos see this Canadian Forest Service Leaflet (PDF).

  • Oak leaf phylloxeran: The damage from oak leaf phylloxera is first visible as yellow spots on the leaves in May and June. This gradually progresses to complete browning and defoliation of some trees by late July. By late July or early August, heavily affected trees lose their leaves, although the trees often produce a second flush of leaves in August.

    Most trees with phylloxera seem to have light infestations without damage, while a few trees are heavily attacked year after year, becoming severely weakened and eventually dying. At least 10 species of predators have been recorded feeding on the phylloxeran, but they do not appear to control it.

  • Winter moth: Winter moths caused extensive damage to deciduous trees on southeast Vancouver Island in the early 1980s, until a biological control program using parasitic wasps and a parasitic fly brought the moths under control. They are also kept in check by native predators such as ground beetles.
  • Gypsy moth: Gypsy moths (Lymantria dispar) evolved in Europe and Asia. They were accidentally introduced to North America, near Boston, in 1868 or 1869. Since then the range of gypsy moths has expanded and continues to increase. Occasionally isolated populations of the moths are found in British Columbia’s Garry oak trees. Read more on gypsy moths.

Many Garry oaks recover from moderate infestations without treatment. However, if you are concerned that your trees are unhealthy, have an arborist with Garry oak expertise check them, as weakened trees may eventually succumb to multiple or repeat infestations.