evergreen – The Garden Professors™

Plants for winter interest: Going for the Gold

Winter appears to have a death grip on the eastern half of the U.S. for the second year in a row. The thermometer on my car read -6 F on my way into work this morning; with lows of -5, -11, and -2 predicted for the latter half of the week. And to my Northwest friends that have been out mowing their grass already, may the bird of paradise fly up your nose. At this point I don’t even remember what my lawn looks like.

Evergreen conifers provide one horticultural escape from the winter blahs. But evergreens don’t have to be green. One group of conifers that can brighten up a winter landscape are yellow or golden conifers. I will acknowledge these plants are not for everyone. But when sited properly (avoid winter sun is a common admonition among conifer buffs) and used judiciously (a little yellow goes a long ways) these conifers can add a contrasting element that can set off a garden. Note: Hardiness zone and size based on the American Conifers Society Conifer database.

Picea orientalis ‘Skylands’ (Skylands Oriental spruce) Zone 4. Size: Large (> 12” per year). This tree is a guaranteed show stopper. The combination of the narrow upright form and golden needles is tough to beat.

Picea orientalis ‘Firefly’ (Firefly Oriental spruce) Zone 4. Size: Intermediate (6’-12” per year). Firefly was selected as a sport off of ‘Skylands’ and is a recent introduction from Iseli nursery. So if you like Skylands but don’t have room for large conifer, this could be for you.

Chamaecyparis pisifera ‘Filifera Aurea’ (Golden thread false cypress) Zone 5. Size: Intermediate (6”-12” per year). This a tough plant that can make a good contrast specimen or can also serve as a foundation plant.

Golden thread false cypress as a foundation planting at the Missouri Botanical Garden

Picea pungens ‘Lutea’ (Golden Colorado spruce) Zone 4. Who says blue spruce have to be blue? Lots of concerns with blue spruce in the Midwest these days (more on that in later posts), but if you’re in an area where blue spruce are still doing well, this is an option for a winter bright spot.

Pinus contorta ‘Taylor’s sunburst’ (Taylor’s sunburst lodgepole pine) Zone 3. Ok, I’m cheating a bit here – the yellow comes on the new growth in the spring and then turns green. ACS database lists as a large conifer but I think they are referring to the straight species. When I have seen this plant it’s more in the intermediate range (6” – 12” per year).

Carrot-top syndrome in white pine

I know a few folks out there are starting to believe that I’m just an apologist for the nursery industry. While it’s true most of the nursery people with whom I work are hard-working folks trying to do their best to run a successful business and produce a quality crop, there are certainly some issues out there and I’ve got my share of pet peeves. One of the things really that chafes my heiney is what I refer to as “Carrot-top” syndrome in eastern white pine (Pinus strobus). White pine is one of the most commonly planted conifers in this part of the world. White pine is native throughout much of the eastern US and is an extremely fast growing tree that makes a good ornamental when planted on the right place with room to grow. It is also widely grown as a Christmas tree in the Upper Midwest as well and therein lies the rub. Many nursery producers also grow Christmas trees and many Christmas tree growers also dig nursery stock. The result? White pines that have been heavily sheared as Christmas trees end up planted as landscape trees. Once in the landscape, the upper portions of the trees will quickly resume rapid growth, with some shoots growing 2’ to 3’ or more per year; while the side shoots that had been repeatedly sheared barely grow at all. After a couple of years the net result is neatly trimmed Christmas tree with a wooly beast growing out of its top. What’s the solution? Ideally producers should identify which portion of their trees will be sold as Christmas trees and which are destined for the landscape trade. Christmas trees can be sheared to meet demands of that market while landscape trees can be pruned much more lightly to maintain a single leader and conical form but keep obvious layers of whorls. The dilemma, of course, is that growers don’t always know which trees will end up and the Christmas tree lot and which will be dug for the nursery trade. The other, more challenging problem is that, given a choice, 99 out of 100 garden consumers will choose the neat-looking Christmas tree for the landscape, unaware of the wooly mess that’s about to be unleashed in their yard. The solution? Education on both sides; making growers aware of the issue and making consumers realize that the only way to have a natural-looking white pine in your yard is to start with a natural-looking white pine.

Heavily sheared pines will retain the outline from from shearing for years while the top rages out of control.

EverGreen or EverYellow?

In last week’s post I mentioned that many tree problems can be difficult to diagnose and require a thorough inspection and site analysis to get to the root of the problem. In contrast, a recent issue that has generated a lot of calls is easy to explain and is not a cause for major concern. Many homeowners and others are alarmed that needles on their white pines are turning bright yellow.

“Is my pine dying?”

The key in assessing this situation is looking at which needles are turning color. Except for southern pines, most conifers produce only one, single flush of new needles each spring. Because of this, we can work our way down a shoot and tell when each group of needles was formed. The outermost needles were formed in the current year, needles in the next internode were formed the year before, needles formed in the next internode were formed the year before that, and so on. Most evergreen conifers keep their needles for 3-6 years and then the needles senesce and fall off. The longest-lived needles, perhaps not surprisingly belong to bristlecone pines, which are also the longest living trees on earth. Bristlecone pines, the oldest of which is over 4,500 years old, have needles that persist for 13 to 17 years. But I digress, back to the white pine. White pine needles last 2 or 3 years. Each fall, many of the previous year’s needles turn yellow and senesce. Since the needles often turn bright yellow and almost half the needles on the tree are affected it can certainly grab attention. As long as only older needles are turning, the process is natural and there’s no need for concern. On the other hand, if this year’s needles are dropping that’s another issue and warrant further investigation.

White pines don’t keep their needles very long. As long as this year’s needles aren’t senescing, the tree should be OK.

Pining to learn more about conifers? The Gymnosperm database http://www.conifers.org/ is an awesome and authoritative site that has information on just about every conifer known to science.