Small Leaves, Light Shade; Big Leaves, Deep Shade

Standard
20171230A Gleditsia triacanthos 'Sunburst' oregonstate.edu.jpg

The shade under these fine-leaved honeylocust (Gleditsia triacanthos ‘Sunburst’) is very light and the lawn grows as well as in full sun. Source: oregonstate.edu

If you want to plant a tree on your property, but don’t want to give up a sunny flower bed or lawn because of the shade the tree will create, consider the following detail: the smaller the tree’s leaves, the more light will filter through; the bigger they are, the less sun reaches the ground.

Therefore trees with tiny leaflets, like honey locust (Gleditsia spp.), black locust (Robinia spp.) and silk tree (Albizia julibrissin) and trees with deeply cut leaves, like  cut-leaved alder (Alnus glutinosa ‘Imperialis’), certain Japanese maples (Acer palmatum dissectum) and cut-leaf birches (Betula pendula ‘Filigree Lace’ and others), let in plenty of light and you can consider the space at their feet as being in very light shade and sometimes, when there are no other obstacles around, the equivalent of full sun.

The opposite is true of trees with very large leaves, like Norway maple (Acer platanoides), basswood (Tilia americana) and red oak (Quercus rubra). They create deep shade, even when they’re young and the shade just keeps getting deeper as they mature. Growing flowers or lawns at their base can be very difficult indeed.

Most other trees have “average-sized” foliage and will give medium shade in their youth, but tend towards deep shade as they mature.

Finally! Japanese Maples for Cold Climates!

Standard
20170713AAcer x pseudosieboldianum North Wind - spring_9099.jpg

Acer x pseudosieboldianum North Wind®

Who doesn’t like Japanese maples (Acer palmatum), with their lacy foliage and oriental look? They’re on pretty much every gardener’s wish list. However, they’re not at all well suited to cold climates.

In hardiness zones 6 and above, as in much of Europe and the south to middle latitudes of the United States, there’s no problem: you can find Japanese maples locally and they’ll form beautiful small trees with multiple branches and dense growth in all by the most exposed spots. In regions colder than zone 6, though, therefore towards the northern limits of  the US as well as most of Canada, they are sometimes sold, but usually fail to thrive.

Sure, you can often keep them alive in zone 5, but they remain stunted, forming small, sad-looking shrubs with only a few branches and scattered leaves… if, indeed, they survive. The small sickly specimens that do make it through cold winters seem to be saying, “Please, someone, end my life. I can’t bear another one of those winters!”

Adding Cold-Resistance Genes to a Tender Shrub

20170713G Acer x pseudosieboldianum Arctic Jade - Summer Tree_6170.jpg

Acer  x pseudosiedoldianum Arctic Jade®

But there’s good news for the northern gardeners who despair of ever being able to grow their own Japanese maple. Hybridizers have been working on developing hardier varieties for decades now and are now putting their creations on the market: Japanese maples that are much hardier than older varieties and are able to reach their full potential in zone 4. In fact, they might even be worth a try in a protected spot in zone 3, especially if you’re willing to deal with occasional winter damage.

By crossing the tender Japanese maple (A. palmatum) with its hardier close relative, the Korean maple (A. pseudosieboldianum), solidly hardy in zone 4, hybridizers have been able to create small trees that resemble Japanese maples with their refined habit and beautifully cut foliage, but that can tolerate winters of at least -30°F (-34°C), the equivalent of zone 4.

They’re so new they don’t even have an official common name and Acer palmatum x pseudosieboldianum is quite a mouthful, so I’ll simply call them “hardy Japanese maples.”

New Hardy Japanese Maples

There are currently four cultivars of these new hardy Japanese maples on the market. Here’s what I know about them:

The Jack Frost® Collection

20170713 Jack-Frost-Logo-300x138 .pngIseli Nursery in Boring, Oregon has launched three cultivars from its hybridization program as the Jack Frost® Collection. They continue to work on the collection and hopefully there will be more hardy varieties to come.

1. North Wind® Hardy Japanese Maple

Acer x pseudosieboldianum ‘IslNW’

20170713C Acer x pseudosieboldianum North Wind - Autumn_5326.jpg

Acer x pseudosieboldianum North Wind® in fall.

This is the most widely available variety, the one you ought to be able to find quite readily in your local garden center. I know it has turned up in garden centers near where I live. Extra-tough and of good size, more upright in its youth, but becoming broader as it matures, it makes a superb small tree or a large shrub. The palmate leaves are reddish in spring, fading to medium green in summer, then turn a fiery scarlet red in fall. The winged seeds too are red, adding a perk of color to the summer garden. To see it is to want it. Retailers have been telling me it simply flies out of their nurseries!

Height: 20 feet (6 m). Diameter: 15 feet (4.5 m). Zone 4.

2. Arctic Jade® Hardy Japanese Maple

Acer x pseudosieboldianum ‘IsIAJ’

20170713D Acer x pseudosieboldianum Arctic Jade - spring leaves_5989.jpg

Acer x pseudosiedoldianum Arctic Jade® in spring.

This cultivar produces broader leaves than the others, rather like those of the full moon maple (Acer japonicum ‘Aconitifolium’). They are incised at the margin and jade green in both spring and summer, becoming orange and red in fall. This maple is on the market, but in more limited quantities than North Wind™.

Height: 20 feet (6 m). Diameter: 15 feet (4.5 m). Zone 4.

3. Ice Dragon® Hardy Japanese Maple

Acer x pseudosieboldianum ‘IslID’

20170713E Acer x pseudosieboldianum Ice Dragon - spring_3073.jpg

Spring growth on Acer x pseudosieboldianum Ice Dragon®

This is the smallest of the new cultivars and also probably the one that most closely resembles our image of a Japanese maple, with its somewhat arching habit and finely dissected leaves. They are reddish in spring and medium green in summer, becoming yellow, orange and red in fall. Launched only in the spring of 2017, this cultivar is currently the hardest to find in nurseries and also the most expensive. It will likely become easier to find and cheaper as time goes by.

Height: 8 feet (2.4 m). Diameter: 10 feet (3 m). Zone 4.

From Other Hybridizers

The only hardy cultivar not developed by Iseli Nurseries is the following, created by Professor Ed Hasselkus at the University of Wisconsin. It was introduced by J. Frank Schmidt & Co. Nursery in Boring, Oregon.

Northern Glow® Hardy Japanese Maple

Acer x pseudosieboldianum ‘Hasselkus’

20170713F Northern Glow .jpg

Acer x pseudosieboldianum Northern Glow™

This is the largest of the hardy Japan maples, naturally taking on more the form of a tree than a tall shrub. Its growth is quite upright at first, then becomes rounded and spreading as it matures. Its palmate leaves are incised along the edges, although not as dissected as Ice Dragon™. The leaves are reddish green in spring and medium green in summer, becoming reddish-orange to dark red in fall.

Height: 20 feet (6 m). Diameter: 24 feet (7.5 m). Zone 4.

More to Come?

I’ve got my fingers crossed that this is only the beginning, that work is being done on transferring the purple summer foliage of the Atropurpureum types of Japanese maple to the hardier hybrids, but only time will tell.

How to Grow Them

20170713F Acer x pseudosieboldianum Ice Dragon - spring_3070.jpg

Acer x pseudosieboldianum Ice Dragon® is the smallest cultivar, definitely more a shrub than a tree.

You’ll find hardy Japan maples easy to grow to full sun to partial shade in any well-drained, slightly acid garden soil. No winter protection is required even in the first year. In fact, like most trees and shrubs, they need little cate at all once they well-established: just water them well the first year to help them settle in.

With their limited size, these new maples will make excellent choices for today’s smaller yards and gardens.

Availability

Every time I write about new plants, I receive messages from enthusiastic gardeners who want to know where to find them … locally. And I simply can’t answer that question. I don’t even know what nurseries and garden centers are found in your neck of the woods, let alone what they carry! I can tell you though that the plants mentioned here are all on the market and readily available to any retail nursery that wants to order them.

If you can’t find these plants, show this article to your local merchant and ask them to order one for you. If they tell you they can’t, it’s not really because it’s impossible, but rather because they don’t want to be bothered. Be a bit pushy and you ought to be able to get them to order one of these beauties for you… probably for delivery next spring.

Best of luck!20170713D Acer x pseudosieboldianum Arctic Jade - spring leaves_5989