|Today in the Garden of a Lifetime: Gloire De Marengo ivy|
The foliage of 'Gloire de Marengo' ivy is the gold standard for variegation—the trifecta of size, vigor, and sharp contrast—except when it isn't. One of the large pots of it in the overwintering greenhouse is covered with new foliage. The fresh young leaves are bright green, all right, but show almost none of the strong gray-and-white variegation of the mature foliage beneath.
Here are some possibilities why. The strength of the sunlight is still comparatively weak, the length of the days is still comparatively short, and this container of Hedera canariensis 'Gloire de Marengo' is in not just a greenhouse, but a double-skinned "hoop" house. Instead of being glazed with true glass, or panels of glass-like polycarbonate, the greenhouse is "glazed" with not one, but two enormous sheets of milky sheet plastic. Strong, durable, and oh-so-economical, the two sheets are sealed together at the edges such that the interior cavity can be kept inflated with a thin layer of air. (Think of a slice of baloney between two slices of bread.)
That layer of air is strongly insulating, and cuts heating costs by at least a quarter. Great! The two sheets of sheet plastic also reduce the strength of the already-weak Winter sun. Not so great, but an acceptable trade-off. The function of the greenhouse is to get plants through the Winter, not to provide so much sun that they maintain peak activity. The greenhouse is only heated to fifty degrees Fahrenheit, too, although it's warmer during the day from passive solar heating. So for both reasons of modest light and modest but frost-free heat, the plants are likely to be dormant.
So it may seem unlikely, in such comparatively dim and cool conditions, that any of the plants are becoming more active at all. Then again, the solar heating during the day can be substantial. And many of the plants aren't completely tropical, as in being hardy only to Zone 10. They're just not hardy in southern New England; they could still be hardy to warm Zone 7 and Zone 8, like 'Gloire de Marengo' ivy.
This new and vigorous new growth, then, isn't the news. It's that the growth isn't variegated. New foliage of 'Gloire de Marengo' that receives strong sunlight is variegated from the get-go. Will variegation appear as these leaves mature? Or will it appear because, as they mature, the strength of the Spring sunlight will also be increasing?
Or are these leaves stuck with being all-green, or very nearly so? Will I need to wait a month, when the sun is that much more powerful, to see variegation even on emergent foilage?
As with the gold-leaved wayfaring tree, a small pair of scissors will help me determine everything. I'll cut a small notch in several of these young green leaves, so that, in a month or two, there won't be confusion that they were grown this Winter, not last season nor a month from now.
By May, if notched leaves are also variegated, I'll know that leaves can change to their adult coloring even after they've emerged and, seemingly, grown to their full size. If not, I'll know that sufficient sunlight during leaf formation is essential for good variegation.
Two things are certain: Foliage grown in higher light will be variegated from the start. And a "well lighted" and, therefore, intensely-variegated, specimen of 'Gloire de Marengo' will always be a vibrant focal point in the warm-weather garden.
Here's how to grow this essential variegated ivy.
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