Thursday, December 11, 2008

Tardily Deciduous

Yes, there is a horticultural term for deciduous plants that hold their leaves into winter: tardily deciduous. As the temperatures get colder these plants will gradually lose more and more leaves until they are nearly bare by mid-winter.

No, these Northern Sweetbay (Magnolia virginiana var. virginiana) magnolias in front of the Visitor Center are not sick! They are just now beginning to lose their leaves as the cold weather has arrived. Sweetbay magnolias are generally not recommended for such a windswept site but because the planting beds are so poorly drained (wet!), this was a good choice here: Sweetbays are hardier if they have constant moisture and are native to wetlands. As these small trees mature (15-20 feet) they will create a more comfortable space to sit in front of the Visitor Center. The sweet scent of their late spring and summer blooms is intensely lemon-like.

Here is an evergreen cultivar of the closely related Southern Sweetbay (Magnolia virginiana var. australis) 'Milton'. You can see its leaves are still dark green above and blue-green below. Severe cold (-10F) can damage the leaves and make them drop. Southern Sweetbays are usually more tree-like (20-30 feet here) and less bushy than their northern cousins.

Can you spot the tardily deciduous plant in this image? It's the front and center ball of olive green: Winter Honeysuckle (Lonicera fragrantissima). As the weather gets colder more of its leaves will discolor and drop. The pinkish brown leaves to the left are the marcescent (dead leaves that don't drop) foliage of the White Oak (Quercus alba) while the dark green plant in the background is the truly evergreen Southern Magnolia (Magnolia grandiflora 'Twenty-four Below').

A close look at a twig of the Winter Honeysuckle shows a swelling bud: it is a flower bud that may open as soon as next month if we have a spell of mild weather. Winter Honeysuckle has very strongly lemon scented flowers that perfume a wide area. The flowers can be damaged by severe cold but the shrub always continues to sprout new flowers until mid-spring. This non-native honeysuckle is not an invasive like many of its cousins. It becomes a huge shrub that can be trimmed up like a little multi-stemmed tree.

Looking out the windows from the Visitor Center the evergreen Southern Magnolias defy the winter season with lustrous green leaves. Few broadleaf plants are evergreen in our climate. These are some of the hardiest selections and we wonder how they will fare if we again have our record low temperatures.

Looking north from the Visitor Center you can see how the landscape around the Visitor Center has many plants with winter interest -- evergreens! The pair of potted plants are Bracken's Brown Beauty Southern Magnolias, the center left plant is an American Holly (Ilex opaca) and the center right plant is a Lacebark Pine (Pinus bungeana). Stay tuned for more on evergreen plants in the next blog...

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