ALNUS (Alder) Betulaceae A. species
HABITAT: Native to Europe, Asia, North America. Zone depends on species.
USES: Garden specimen, streamside, lake fronts, furniture, and lumber.
HABIT: Hardy, deciduous trees to 75' which flourish in wet or boggy land. Best grown in cooler portions of N. America only. Fast growing and often has multiple trunks. Foliage opens early in the spring and drops late in the fall. Male and female yellow-green flowers appear in scaly clusters (Catkins) on the same tree prior to leaves. The 1" female Catkin becomes brown, cone-like, and clings most of the year. It can be used in dried floral arrangements.
SEED GERMINATION AND CULTURE: Sow A. glutinosa as it is ripe, but place seed of all others in the refrigerator for 3 months, then germinate at 65-70 degrees Fahrenheit on Park's Grow Mix, covering lightly. Transplant when large enough to handle to 2 1/4" peat pots; shift to 4" peat pots when roots emerge from pot walls. Grow in a protected spot (cold frame) until small trees are well enough established to be placed in permanent locations. Seed may also be sown in a protected area (cold frame) in March or April. Set out in light shade or full sun in moist to wet soil. Keep moist at all times. Feed early in the spring with a fertilizer such as 10-10-10 at the rate of 2 lbs. per 1" of trunk diameter. Punch holes in soil around the tree 18-24" apart and 12-18" deep; place holes at the drip line (2/3 of the distance from the trunk to the outer edge of the leaf line). Keep sprayed for insects and diseases. If pruning is needed, do so in winter or early spring. Prune young trees to a central stem and shorten the side shoots. As trees increase in height, gradually remove lower branches until desired height of a clear trunk is achieved. This pruning may be done in the summer.
SPECIES: A. cordata (Italian Alder): 45'. Zone 5. Dense. Glossy, green foliage. Rounded habit. Grows well in drier soil. Southern Italy. Spread 20-30'.
A. glutinosa (European Alder): 75'. Zone 3. Wet soil. 4" leaves. Variety Laciniata leaves are deeply lobed (Cutleaf European Alder).
A. hirsuta (Manchurian Alder): 60'. Zone 4. Vigorous. Japan, Manchuria. Pyramidal.
A. incana (Speckled Alder): 60'. Zone 2. Europe, North America. Often shrubby. Moist to wet soil. Several varieties available.
A. rhombifolia (White Alder): 75'. Spread 30-40'. Zone 5. Wet soil. Western N. America.
A. rubra = A. oregona (Red Alder): 60'. Zone 4. Far West. Wet soil. Variety pinnatisecta (Cutleaf Red Alder) deeply lobed. Spreads 30-40'.
A. rugosa (Hazel Alder): 40'. Maine to Texas. Alternate leaves. Shrub. Streams, pond sites.
INSECTS: Flea Beetles: Use an approved insecticide such as Sevin.
Aphids: Use an approved insecticide such as Malathion.
Borers: Keep plants fertilized. Keep watered and cultivated. Wrap newly planted tree trunks. Spray leaf eating insects with Sevin, Malathion.
DISEASES: Root Rot: Destroy infected plant parts. Sterilize soil.
Canker: Prune and destroy infected leaves. Dust with Bordeaux Mixture, Lime-Sulfur, or Copper Spray. Keep watered during droughts.
PROPAGATION: Grafting, seeds.