Companion Plants: Propagating the Arbutus Tree
Nanoose Bay, British Columbia
Reprinted from the Mt. Arrowsmith Chapter Newsletter, Vol. 10, No. 9, 1998.
Our beautiful Arbutus menziesii is a valuable tree in the coastal environment, supporting birdlife and enriching biodiversity of the Coastal Douglas Georgia Basin region. As digging one up is rarely successful because of the tree's susceptibility to transplant shock, perhaps you can consider the following and attempt to grow one from seed. Available in nurseries recently, these too are risky to transplant and have a high failure rate.
Understanding their basic needs, you will realize that not every property has a place where the arbutus tree will survive. An area of undisturbed soil, preferably near the roots of a large tree, would be the most promising.
The arbutus is dependent on an underground ecosystem, forming a partnership with mycorrhiza in the soil. Mycorrhiza means "fungus root" and refers to the joining of fungus and tree roots in a mutually beneficial partnership. Without the mycorrhizal networks underground, the ability of the plant to absorb water is greatly decreased. This may sound like a lot of science - and it is.
While these mycorrhizal associates are not fully understood, it is established that the arbutus is dependent on ectomycorrhizae which have their fruiting bodies (puffballs, mushrooms) above ground. (Maples, ash, elms and sycamore can survive under blacktop because their mycorrhiza are endomycorrihiza, which does its fruiting underneath the ground.) For this reason it is important you choose a site that has not been cultivated or subject to heavy traffic. Trees such as arbutus, pine, oak, and beeches need the ecto-variety which can be killed by soil compaction.
Accepting that the underground ecosystem is just as important to plants as the above-ground environment is to us emphasizes the importance of establishing an arbutus tree in a suitable area. The mycorrhiza form a "living network" of interdependency, so the site is crucial in planning to include one in the garden.
Most people would guess that the giant redwood tree, weighing up to 2,000 tons, is the largest member of the plant kingdom. Few would guess that there are larger single organisms underground. Scientists have discovered one in a hardwood forest in Michigan, a species of honey fungus, which covers 37 acres. Among many known large fungal masses, this one is estimated to be at least 1,500 years old, derived from a single spore long ago.
Mycorrhizae are relatively fragile but, when thriving in a high organic soil, they help plants become vigorous, salt tolerant, less fertilizer dependent and able to tolerate chronic low moisture; thus we realize the arbutus tree's dependence on this symbiotic relationship. The tree supplies the fungi with essential sugars all year round.
I have observed that mature arbutus trees surrounded by lawn will often die and used to think the cause was over watering. The problem is more likely that the tree's ability to utilize water is hampered. Arbutus trees need a lot of water and you will notice that many of them are stressed this year after the El Nino dry winter of 1997-1998. Even with the fungi's assistance in supplying it during periods of drought, ample water ensures growth of a young tree and the production of new leaves and fruit in older trees. A healthy native ecosystem is resistant to weeds. In this case, the lawn grass is a weed. Grass does not grow in a healthy ectomycorrhizal soil.
While we cannot produce the necessary ingredients, hopefully you will be able to select an undisturbed site on your property. (I should mention that a commercial mycorrhiza is being used in Southern California to inoculate the soil in restoration of ecosystems and re-vegetation with native plants.)
Arbutus trees can be propagated from seeds as well as cuttings, although the growth is slow with a high failure rate. The germination rate of seeds is over 90 percent. Early winter is a good time to harvest arbutus berries. As birds are responsible for spreading the seeds, an imitation of this process is in order. Soak the berries in water for 24-49 hours until the pulp is soft and can easily be separated from the seeds when spread on clean paper. The sharp little seeds can then be placed in damp peat moss or clean sand and left in the refrigerator for 60-90 days. When heavy rains of winter are over, sow on the surface at your chosen site. A sprinkling (they need light to germinate) of sand and some chicken wire will prevent disturbance by birds, etc. When seedlings emerge later in the season (they may take a second winter to germinate) let survival of the fittest rule - leave the strongest plant in situ and never let it dry out the first few years.
Diane Pertson, a member of the Mt. Arrowsmith Chapter, resides in Nanoose Bay, British Columbia.