A Gardening Journal

Today in the Garden of a Lifetime: Colorful Stems of Golden European Ash

Fraxinus excelsior Aureifolia upper tips not rounded 11 10 15 640

 

Some trees are even more interesting after their leaves have fallen. Then, striking details of bark, bud, and branching are on full display right through until Spring. Some years ago, I introduced golden European ash. Fall to Spring, its leafless young stems sport chalk-yellow bark and are studded with pointy black leaf buds.

 

The tree has been so slow-growing that I didn't return my focus to its cold-weather show until this month, when I noticed a new detail: The tips of many but not all of the branches are swollen, as if they were preparing to expell an impressive spit-ball in Spring.

 

Fraxinus excelsior Aureifolia rounded stem tips overall 11 10 15 cropped 2

 

In the shot below, another swollen tip, oriented at ninety degrees to the one above. The prominent ebony-black buds are killer; another swelling is developing just above the second pair of side buds.

 

Fraxinus excelsior Aureifolia rounded stem tips overall 11 10 15 640 cropped

 

Because the tree's branching pattern is fairly orderly and upright, the stem tips are all the more prominent, and the bulbous ones particularly so.

 

Fraxinus excelsior Aureifolia rounded stem tips overall 11 10 15 640

 

Crouching down for a lower shot, below, I captured the duller-yellow bark of the tree's oldest portions: its trunk and the bases of the main branches. The tips of the short, slender, low side-branches aren't swollen, but those of a vigorous new stem at the lower right of the trunk are. Out of frame at the top, the tips of the newest and tallest stems are also unswollen, even though they are the opposites in vigor, placement, and youth to those also-unswollen lower side branches. Curiouser and curiouser.

 

Fraxinus excelsior Aureifolia overall 11 10 15 640

 

If I could identify a pattern, I might be able to prune this Fraxinus excelsior 'Aureafolia' to enable more and more of its stems to develop bulbous tips. One commonality: The bulbous tips are always at the end of branch segments that are still young enough to wear the brightest bark. Encouraging more new stems is, somehow, part of the answer to having more stems with swollen tips.

 

But not all new stems behave the same. The tips of stems that are not the quickest growing are more likely to swell. If fastest-growing tips were most likely to swell, then the tips at the very top of the tree would be the most swollen: Their branches seemed to have elongated a foot or two just this Summer.

 

But the tips of stems that are really slow growing aren't swollen either. If slow growth made swelling more likely, then the short twigs arising from oldest and less-colorfully-barked portions of the lower limbs would be bulbous instead of pointed.

 

Putting these vague observations together, it would seem that stem tips that are growing only medium-fast, and in the broad middle of the tree, are the most likely to swell. Because swellings didn't arise at the out-of-frame tips of those fast-growing vertical stems, there wouldn't be any benefit to turbo-charging growth by a radical pruning-back of the entire tree. Besides, such global pruning would also remove all the tips that are already swollen.

 

Whatever the shapes of their tips, the stems will be showy all Winter long—and, yet, Fall is the recommended time for pruning, not Spring. Drat: Any pruning will remove some tips, let alone the colorful stems they are attached to. Alas, it isn't possible to remove just the lower, older, duller-barked portions of branches, and then re-attach the fresh upper portions to the cut surfaces of the remaining basal growth. To maintain a reasonable amount of Winter interest—which is directly related to the number of young branch tips—I'll need to prune only selectively.

 

First to go, the tall vertical stems that are the leaders of most of the branches: Their tips aren't swollen, and their removal will encourage more side stems, many of whose tips are. Next, the upper portions of a couple of the remaining multi-branched stems (bulbous tips and all) in hopes of encouraging still more stems to emerge from the lower portions of the tree. Since this growth will be in the tree's broad middle, perhaps many of its tips will be bulbous. The rest of the stems—especially those with swollen tips—will be untouched.

 

Below, the pruned golden European ash.  The boxwood hedge is about five feet high, but I might grow it several feet higher, especially if the display of the Fraxinus becomes truly exciting—and persistently high despite my pruning.  Stay tuned for an update next Summer, when whatever new stems will emerge as a result of this pruning, and from, simply, another new growing season, will have done so.

 

Fraxinus excelsior Aureifolia overall 2015 11 13 640 

 

But what about those pruned stems? Below is an assortment, with one of the bulbous-tipped ones above all the tall straight-tipped stems that were the leaders.

 

Fraxinus excelsior Aureifolia tips of cut stems 111315 640

 

Come Spring, growth will resume, and the mystery of the swollen tips might be resolved. When new growth emerges from their black tip-buds, does the swelling remain or reduce? If it did decrease, that would be consistent in concept, if perhaps not actual biology, with my description of a swollen stem as getting ready to eject a bolus of...something...in Spring. And maybe new growth is that something.

 

Fraxinus excelsior Aureifolia swollen tip exterior 111315 640

 

Because I'd already sacrificed one of the swollen tips in my pruning, I didn't hesitate to slice into it to reveal some details of its interior.

 

Fraxinus excelsior Aureifolia swollen tip interior 111315 640

 

There appears to be no sign that the swelling is formed from a congestion of next season's pre-emergent growth. The interior of the swelling is woody, not soft, i.e., it isn't some sort of launch pad or staging area for speedy soft growth next season. It's all set up, all formed; already, it is what it has been intended to be.  "I'm bulbous, therefore I am."

 

Or maybe this tree's unusual growth pattern is stilll revealing itself. Maybe my current pruning strategy—to remove tall straight stems and not much else—won't produce many new swellings. Only by following this tree more closely year by year will I be able to grasp the full details of its so-cool performance in the cool months—and then, with still more years of pruning experiments, maximize it.

 

A golden European ash bearing countless young yellow twigs, many or most of which have swollen tips, sounds like the project of a lifetime. I'm on it.

 

 

Here's how to grow golden European ash, as well as shots of its colorful stems when they were several years younger, when none of them was swollen at the tips.

 

Here's how exciting this tree's growth is in Spring and Summer.

 

Here's how exciting this tree's growth is in Fall.

 

 
 
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