Molly Nemec
Chisago County Master GardenerWhat influences fall color? The variety and intensity of fall colors depend on the weather. Watch the temperature before and during the time leaf chlorophyll is dwindling.
Days that are warm and sunny, along with nights that are cool and crisp, but not freezing, will create the most brilliant color display. The leaf produces a lot of sugars on warm days and the leaf veins slowly close during cool nights.
The closing keeps the sugars from moving out. Sugar and sunlight produce anthocyanins, which turn leaves red and purple. Carotenoids are always in leaves and yellows and golds remain fairly constant from year to year.
Soil moisture also affects tree color. Early showings of color can be caused by cool, wet summers. The reds may not be as brilliant when autumn has lots of warm, cloudy, rainy weather.
The leaves make less sugar in the reduced sunlight. This is because the sugar moves out of the leaves during warm nights and the leaves have less of it to form anthocyanins and turn red and purple.
A mild drought can brighten the display, but severe drought may make colors duller. Sometimes, the leaves die early from a lack of water.
Leaves may not have as much pizzazz if pests, disease and environmental problems have damaged them.
Which trees should be planted for color in my own backyard?
Maples offer the most intense fall color! For red leaf color, ask someone at your nursery about the cultivar ìAutumn Blazeî (Acer + fremanii). This colorful and fast-growing tree combines the best traits of its parents--silver and red maple.
The sugar maple (Acer saccharum), also known as the Wisconsin State Tree, grows slower than the red maple but is desirable for its symmetrical form. It turns anywhere from yellowish-orange to bright red. The cultivar ìLegacyî shows off brilliant fall color.
The amur maple (Acer ginnala) is an ornamental tree ideal for smaller spaces. It has dainty leaves and exhibits colorful red fruit in summer. Fall color is orange-crimson to deep purple. Look for the varieties ìEmbersî and ìFlame.î
The silver maple (Acer saccharinum) is the fastest growing maple and is a very good shade tree. The cultivar ìSilver Queenî is gold in autumn.
Among the oak trees, red oak (Quercus rubra) is an excellent choice for a yard, given its strong wood and glossy leaves that turn burgundy in autumn.
Pin oak (Quercus palustris) is one of the fastest-growing oak trees. This tall, symmetrical tree with pyramidal form displays reddish-brown leaves in the fall.
Though the pin oak and red oak varieties offer rich fall color, they are also susceptible to ìOak Wilt.î Oak wilt is a fungal disease that is spread by beetles and affects the treeís vascular system.
Pruning oak trees in February and March and avoiding pruning in the summer months will help prevent this deadly disease from spreading.
In the white ash family (Fraxinus americana) ìAutumn Blazeî and ìAutumn Purpleî are cultivars that were selected for their deep green leaves that turn reddish-purple in fall.
There are several shrubs that can add dazzling color to your landscape.
Burning bush (Euonymus alata) is a large shrub with unsurpassed, bright-red foliage in the fall. Highbush cranberry (Viburnum trilobum) sports small, fiery-red berries in late summer and red foliage in autumn.
Popular cultivars include ìAlfredoî and ìCompactum.î Dwarf summer-blooming spirea (Spiraea japonica) is covered with flat clusters of flowers and yellowish-green foliage in summer. It turns from soft pink to reddish-orange in autumn.
The cultivar ìGoldmoundî is a neat, compact shrub that looks nice near buildings and in mass plantings.
Autumn is a great time to scout out nurseries in search of trees with fabulous fall foliage! This will help you landscape your yard with an array of color.
Plan not only for fall color, but winter, spring and summer as well. Many of these aforementioned ìall starsî will amaze you and beautify your yard all year long!.
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