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Elisabeth C. Miller Library

Keyword: Eucalyptus

Toxicity of Eucalyptus trees

I have a young Eucalyptus pulverulenta tree. I’m concerned that it might be emitting toxic chemicals into the surrounding soil that will harm other plants. Is this indeed a cause for concern?

My instinct is that your Eucalpytus tree will probably not be toxic to most other plants. Eucalyptus is often seen growing in the midst of garden beds here in Seattle, to no ill effect. I have a tree growing in a perennial bed, and have noticed no problems. However, the leaves do contain essential oils (phenolics and terpenoids). This does make the tree more flammable, if that is a concern. Eucalyptus leaf litter (to a greater degree than exudates from the tree’s roots) can inhibit specific food crops, like wheat. This is what is meant in this University of Florida Extension article (now archived), which refers to “selective activity of tree allelochemicals on crops and other plants.”

To show how selective this chemical property can be, see the following documentation of a University of California, Davis experiment using composted Eucalyptus as mulch.

Excerpt:
“Mulch products made from Eucalyptus are an asset to maintenance of fine landscapes. Composted Eucalyptus makes an excellent seed cover and will aid in germination and establishment of seedlings such as California Poppy. Fresh Eucalyptus is an excellent mulch for woody landscape plant materials and palms; the main effects of its use are weed control and water conservation.”

Unless you are growing your tree in the middle of a field of wheat or among other grassy plants, your landscape is probably in no danger of inhibited growth from the Eucalyptus.

You may find the following veterinary perspective (from Cornell University) on the toxicity of Eucalyptus of peripheral interest.

Eucalyptus care

I recently purchased two Eucalyptus gunnii trees and one E. dalrympleana, which are still in their pots. I have them in full sun, facing south. I have been watering them every day – is this appropriate? I know that the gunnii tolerates waterlogged soil.

 

All Eucalyptus prefer full sun and well-drained soil. They are very drought tolerant when established.

Source: Manual of Woody Landscape Plants, by M. Dirr, 1998, p. 352.

If your plants are in terracotta containers they will need daily water. If they are in non-porous containers you have a bit more leeway, but do not let them dry out while they are young.

Another consideration is whether you plan to grow these trees in containers permanently, or if you are going to be moving them into the garden. If you plan to keep them in pots, bear in mind that these trees will get quite large (70 feet tall by 20 or more feet wide), so you may end up needing to do a lot of pruning from the top as well as root pruning. Sometimes, even when planted out into the garden, urban gardeners with small lots will coppice a tree like Eucalyptus gunnii or E. dalrympleana annually so that it does not overgrow its site, and so that the rounded, juvenile leaves are maintained. See the Royal Horticultural Society’s page on eucalyptus pruning for additional details.

If your plan is to move the trees into the garden, it is best to do it when they are relatively young and small, as Eucalyptus generally dislikes root disturbance.