What factors influence autumn leaf color?

Molly Nemec

Chisago County Master Gardener

Autumn leaf color depends on the temperature and amount of precipitation in late summer and fall.

The temperature before and during the time chlorophyll dwindles in leaves is a key factor. Warm, sunny days with cool, crisp nights create the most spectacular color display.

Leaves produce a lot of sugar on warm days. At night, leaf veins slowly close, which keeps the sugars from moving out.

Sugar and sunlight cause the production of anthocyanins, which turn leaves red and purple. Red may not be as striking when autumn is rainy and cloudy, because the leaves make less sugar in the reduced sunlight. During warm nights, sugar moves out of the leaves, so the leaves have less of it to form anthocyanins.

Soil moisture also affects tree color.  Some early displays of color can be attributed to cool, wet summers.  A mild drought can brighten the display; a severe drought may make colors less intense. Extreme lack of water causes leaves to die early.

Pests, diseases and environmental problems also contribute to lack of foliage brilliance.

What should you plant for great fall color? Maples offer the most vivid hues. For red foliage, look for the “Autumn Blaze” cultivar (Acer fremanii).  This fast-growing hybrid combines the best traits of its parents, silver maple and red maple. Another beauty, “Northwood,” offers showy red flowers in early spring and brilliant orange-red leaves in the fall. Very cold hardy, it is an excellent performer in northern areas. “Firefall” is a University of Minnesota creation known for early fall color, ranging from orange to fiery red.

The sugar maple (Acer saccharum), also known as the Wisconsin State Tree, grows more slowly than the red maple but is long-lived and symmetrical. It turns anywhere from yellowish-orange to bright red. The cultivar “Legacy” shows off impressive fall color.

The amur maple (Acer ginnala) is an ornamental tree for smaller spaces. It has dainty leaves and colorful red fruit in summer.  Fall color ranges from orange-crimson to deep purple. Look for the varieties “Embers” and “Flame.”

The silver maple (Acer saccharinum) is the fastest-growing maple and makes a very good shade tree. The cultivar “Silver Queen” is gold in autumn.

Among oaks, 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 burnt-
colored leaves in autumn. Remember that pin oak and red oak are also susceptible to oak wilt, a fungal disease spread by beetles. Pruning oaks in February and March (never in summer) can help prevent this deadly disease from spreading.

In the white ash family (Fraxinus americana), “Autumn Blaze” and “Autumn Purple” are cultivars that were selected for their deep-green leaves that turn reddish-purple in fall.

Several shrubs can add dazzling color to a landscape.  Burning bush (Euonymus alata) is a large shrub with unsurpassed, bright-red to crimson-colored foliage in autumn.

Highbush cranberry (Viburnum trilobum) sports small, fiery-red berries in late summer and red foliage in autumn.  Popular cultivars include “Alfredo” and “Compactum.”

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 “Goldmound” is a neat, compact shrub that looks nice near buildings and in mass plantings.