How fast can they grow?
Eucs, in general, are much faster growing than most other trees in cultivation. Most euc species can be expected to achieve 6 - 12 feet of new growth each year. Exceptions include some of the snow gums (E. pauciflora and its subspecies, E. gregsoniana, etc.), which usually take a couple years to establish, during which they may only grow a foot or two each year; and a few other unique species such as E. vernicosa, E. stricta, etc. which are quite slow growing. (These exceptions are all noted in the euc species index.) But even many of the snow gums will pick up to 4 - 6 feet per year once they are well established.
So, if you have planted a large or rootbound euc, and you are pleased that it has grown 3' in one year, you should not be (in the opinion of this euc grower). Because if you had planted a small one, it would grow much faster. 3' per year may be an acceptible growth rate for many ornamental trees, but for most euc species it is quite pathetic.
What enables eucs to grow so fast?
First, eucs have it much easier in cultivation than they do in their natural habitat in Australia. In cultivation they are not tormented by grazing kangaroos, koalas, and all sorts of insect pests. In addition, most gardens and landscapes offer good soil, and freedom from competition with grass and other trees - neither of which they usually get in their homeland.
Second, eucs do not "harden off" or "go dormant" in the way we usually think of trees preparing for the winter. They are able to grow whenever they have access to water and a little warmth, regardless of what time of the year it is. This is quite different from the regime of most other trees, which do most or all of their growing in the spring and early summer, and then stop. In addition, if they do stop growing for any reason (whether it be summer drought or winter cold), they do not require a certain "resting period" or period of dormancy before they will resume growth again.
The other factor, besides being potbound, that can cause eucs to grow much more slowly than they might, is competition from grass and weeds in the garden. If a euc is planted in a pasture or lawn with grass growing right up to the base of the tree, it will grow much more slowly than in good garden conditions. However, they are able to recover from this condition much more quickly than from being rootbound or overgrown in a pot, if the problem is corrected. A good heavy mulch around the base of the tree will help immensely.
Reasons for planting them small
First, planting them small avoids the problem of their growth rate being stunted. Eucs are unique among trees in that they take many years to recover from being rootbound in a pot, or being planted too large! In some cases, they may never recover. Normal trees may take a year or two to recover from being rootbound, but for eucs the problem is greatly amplified. Although I cannot explain why this is so based on the technical physiology of eucs, I have learned over the years to have nothing to do with large or rootbound eucs. (Some subtropical and tropical species are exceptions, and are better able to recover than the hardy species covered on this page.) Generally, though, eucs should not be grown by the conventional manner for other landscape trees.
Second, large plants with not enough
root mass are often unstable and liable to blow over in a windstorm.
This problem is often difficult to correct except by cutting the tree back
to reduce its top-heaviness, in which case you might as well have planted
a small one. Staking to correct this seldom works, since it causes
the development of a weak trunk - in fact, staking is often largely the
culprit for trees that blow down. (There are certain ways that staking
can be used, as mentioned elsewhere on this page.)
One frequent objection among people who like to push the limits of what can grow in their climate is that they believe starting with a larger plant will give it a better chance of surviving the winter, since larger plants are generally hardier than smaller ones of the same kind. Planting large specimens for this reason is commonly practiced with hardy palms and other "tropicals" in climates where their survival is marginal.
Indeed, it is true that eucs, like most other plants, are more able to withstand cold when they are larger and have some mature wood. But it is still not generally worthwhile to plant large ones because they will not establish quickly and, in the long run, remain vulnerable for a larger number of years.
For example, a small tree (say, 1' tall) planted in the spring may grow to 8' tall its first year, 18' tall its second year, and 30' tall its third year in the ground. Whereas a large potted tree (say, 6' tall) of the same species, and planted at the same time, might grow to 8' by the end of the first year, 11' by the end of the second year, and 15' by the end of the third year. Then let us suppose the following winter is a severe one - the large-planted tree will be more vulnerable. That is really quite a realistic prediction for the fate of those trees, as the following evidence suggests.
EVIDENCE IN FAVOR OF PLANTING EUCS WHEN SMALL
My own trials with large and potbound eucs
My experience with large and potbound eucs is limited, since it did not take me too many tries to figure out that potbound eucs are really not worthwhile at all. However I have done some fairly controlled experiments with E. dalrympleana (and a couple other species).
In June 1996 I planted a Eucalyptus dalrympleana (let us call it "Tree A"). At the time, it was 28" tall, and rootbound in a 1-gallon pot. By September 1998, it was still only about 5 feet tall. Then in December 1998 it froze to the ground.
In August 1997 I planted another E. dalrympleana ("Tree B") out of a 4" pot - it was only about 10" tall. It grew to about 28" by that winter, and then proceeded to grow to about 13 feet by December 1998. Sadly, it also froze - even though it was much larger than the other tree, it was still not quite large enough to make it.
So, to chart the growth rates of
size at planting
Tree A has now grown back from the
base and since I have taken very good care of it over the last couple of
years, it appears to be on its way to making 7 or 8 feet of growth this
year - still not as fast as it should, but it may make a nice tree yet.
Tree B did not grow back after the freeze. I believe it may have
been a rather cold-tender provenance to begin with, since the juvenile
leaves looked an awful lot like those of E. viminalis.
The picture at left (sorry for the poor photo quality) is Tree A in September 1998. (I did not get any pictures of this tree when it was younger.) The picture at right is the same tree in July 2001. Even though it has had 2&1/2 years now to grow back after freezing to the ground, it is still not all that big (about 8' tall). But it is doing much better than it did in its "first life."
The left picture is Tree B in December 1997. In the right picture, the left tree is Tree B in September 1998. It is about 10' tall in this picture and grew a few more feet before it froze that winter. (The other two trees at right are E. viminalis, which froze, and E. parvula, which was not damaged.)
In July 1999 I planted several more E. dalrympleana as small plants from 4" pots. Since then, they also have produced similar results to Tree B, putting on over 10' of growth in one year. After just two years they are about twice as tall as Tree A.
I could relate similar experiences with E. coccifera and E. perriniana.
I have also had problems with large planted eucs and wind. I did have several eucs (E. bridgesiana, E. regnans and E. perriniana) that were in large pots and a bit top heavy, but at the time I did not think they were completely irrredeemable, so I planted them. They were in the ground for a couple years, and eventually seemed to recover somewhat (though not entirely) from having been large-planted - by summer 1998 they were making fairly substantial growth, but still not as much as a small-planted plant could have produced. Just when I was getting optomistic that their recovery may have been worth the wait after all, several moderate windstorms with gusts of about 50 mph blew them over in November 1998. The E. regnans, in fact, was so unstable that it was ripped completely out of the ground and deposited several feet away, trunk and all.
It was then obvious to me that because they were planted large, they failed to develop the strong root systems that they would have if they had been planted smaller. (The E. bridgesiana actually recovered, after freezing to the ground that December, and is now quite a sturdy tree after having to start over.)
Bruce Ritter's Experiment
Bruce Ritter is the owner of Northern
Tropics Nursery in Mt. Sinai, New York. He had been keeping his
eucs in pots, in order to grow them to a large size before planting them
out. I suggested that he try planting them at a smaller size and
watching how fast they grow. He writes:
|Here is the result of a small study
I did, regarding Eucalyptus camphora:
I had a total of four plants. They were all approximately one foot tall, in six inch pots, and recently transplanted from four inch pots, so therefore were not root bound.
I planted one at an eastern location with half day sun, in June. Another went into an area by a low fence to the north, also with half day sun due to the sun coming over the fence. This went in in early July. It must have by that point become somewhat rootbound, because its roots were coming out of the pots and growing into the ground. I snapped a large one when pulling it out of the cold frame. The other two plants were left in the six inch pots, and given a southern exposure with protection from high noon sun by the top of the cold frame. Here are the results:
June planted plant: Now almost six
What's more, the six foot plant is starting to make woody growth, which I would assume is very important to help survive the winter.
CONCLUSION: In spite of my initial doubt about [the] description of rate of Eucalyptus growth; after doing a small, but controlled study, I am convinced that setting out young plants with ample room for the roots is the only way to get a significant rate of growth. And yes, throw out those root bound plants and start with fresh healthy ones. As a side note, another Eucalyptus I was growing, E. glaucescens, is now five feet tall, while the potted ones were thrown out two weeks ago at only one and a half feet tall.
The next step will be comparing the survival rate of the four E. camphora plants. I will give the two planted ones identical protection, but the other potted plants will be in the cold frame. This part of the study may not be as reliable, because the medium size plant will not receive much light during the winter, as the sun will dip below the fence. But so far, I am impressed with the results.
A couple months later, Bruce writes:
|Well, the final conclusion is in. The Eucalyptus camphora that I planted this spring at about eight inches tall or so, is now EIGHT FEET tall. The one that I planted only a few weeks later, but root bound is still only two feet tall. How is that for growth? I must admit that I am completely overwhelmed. The trunk is about an inch thick. . . Probably, what I will do is plant a E. debeuzevillei next to my five year old one, and see if it overtakes it during the summer. I have no doubt that it will.|
Sadly, this Eucalyptus camphora, as well as most of the other species he was growing, were severely damaged by cold temperatures the following winter. He needs hardier seed provenances! Also, his plan with the E. debeuzevillei might have been slightly disappointing since it is a snow gum and does not grow quite so fast as most other euc species.
Quotes from Eucalyptus Nurseries Ltd.
Nurseries Ltd. is a grower of eucs in Wales with more than 17 years
of experience in the business. They have stated some truths about
this subject so eloquently, that they are very much worth quoting here.
|"Large Eucalyptus plants
grown conventionally. . .are a liability. . . Large plants in small pots
are usually pot-bound, take a few years to recover and are often subsequently
unstable. In rudimentary experiments plants of the same species that
had been grown on for two years in 12-inch pots and were about 5 feet high
were planted out and compared with younger plants of 14 - 18 inches high
that had experienced no check due to root restriction. The smaller
plants overtook the larger pot-bound plants in less than one season and
continue to outgrow them."
"Also the common problem with eucalypts planted too big with a small root system is that there is an imbalance of root and shoot and the root fails to catch up with the top growth. . . It is certainly not advisable to plant large eucalypts. . .for these reasons."
What size tree to choose and what to avoid
When selecting a euc to purchase, look for the following desirable traits:
Here are two eucs in 1-gallon pots that would be suitable for planting out. The one on the left (E. neglecta) is slightly on the small side and will have no setback of the growth if planted now. The one on the right (E. glaucescens) is slightly larger than would be ideal and will be set back just a little, but is still not too unsuitable for planting. Both are generally healthy and vigorous.
Here are two eucs in deep 4" pots, E. dalrympleana (left) and E. nicholii (right). Both of these are very healthy and ready to go in the ground. If planted now, they will be very well-established in a matter of weeks. (In fact, since I planted that E. nicholii in my garden just after taking this picture, I can personally attest to this!)
Avoid purchasing eucs that show any of the following problems:
Here are two eucs, both E. parvula, that have grown too large for their pots and should not be used. The tree at left is in a two gallon pot, but has grown to at least 3' tall. Even though it appears to be healthy now, it is probably quite rootbound and its growth will still be slowed significantly. The tree at right is certainly very rootbound - fortunately the nursery is using it strictly as a display specimen rather than trying to sell it.
If you do get a euc that falls short of these desirable traits (in the first list), it is not necessarily destined to fail. Information about how to correct these problems continues under Cultural information for growing Eucalyptus in cool climates.
Finally, remember to plant it immediately after purchase (at least within a few days). They grow so fast that leaving it in the same pot for even a couple extra weeks can greatly effect how rootbound it becomes, and how vigorous it is when planted out.
Future possibilities for planting large trees
Small trees have the disadvantage of not providing as much of an instant effect in the garden as a larger tree. In addition, they are not sufficiently ignoramus-proof in commercial landscapes. Trees that are not fairly large to begin with run the risk of being trampled, sprayed (by someone who thinks it's a weed), or severely pruned (by someone who thinks it's supposed to be a shrub). Since customers often demand larger specimen trees, it is certainly worthwhile to find ways to grow larger trees that will still be suitable for planting. This will also allow their planting in more public places, once contractors catch on.
In spite of all my dire warnings
against planting large potted trees, more recent evidence would suggest
that there are ways to make it successful. Trees that are grown to
several feet tall in large pots, and that have sturdy trunks (i.e.
not staked), may still make successful trees without much of a growth check.
(The large E. glaucescens at Steamboat Island Nursery, pictured
was grown by this method.) Most importantly, the top growth must
not be out of proportion with the root mass. Regardless of the size
of the rootball, it must still contain a great many roots throughout; they
cannot all just circle at the bottom. One possible way to achieve
this in the nursery would be to withhold nitrogen and fertilize more with
potassium, phosphorus and micronutrients. The consistency of the
soil media should also be designed for maximum root density.
|Eucalyptus Nurseries Ltd. in Wales has even been successful with very large containter-grown trees. For more imformation, click here. (Please note that Eucalyptus Nurseries is not able to sell plants to the USA.) These trees have been grown according to a very special technique, resulting in some plant characteristics admittedly quite contrary to the guidelines I have set for suitable plants.|
Of course, most large eucs commonly found in nurseries are still unsuitable, either because the size of their root system is not sufficient to support the top growth, or because the trees have been staked and are weak and unstable. I would still urge the buyer (and the nurseryman) to be very cautious about this.
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