Poplars

All poplar species are known for their fast growth rate. Some are reported to grow as much as 6’ in one season, though 18-36 inches is more common in our area. They are also extremely winter hardy and seem to grow fast despite dry conditions and high wind. This makes them popular for wind shelters, pastures, and parks.

The fast growth rate does come at a price though, resulting in a shorter life and weaker branches. Although some poplars can live well over 100 years, many have an average lifespan of about 30-50 years. Typically, the faster a tree grows, the more susceptible it will be to pests and diseases. Slowing down the growth rate by not fertilizing heavily can help reduce disease pressure and increase the life of your trees.

Rapid crown growth coincides with rapid root growth. Poplars tend to have large and aggressive root systems. They are known to disturb sidewalks, concrete slabs, and septic pipes.

Quaking Aspen

One of our most popular trees due to their smaller size and fast growth habit, it should be noted that aspen have a high tendency to sucker. Although suckers can be mowed and clipped to keep a tidy appearance, potential homeowners should be prepared for this continual maintenance. If clipping is not for you, consider using aspen in a small grove where you can allow the suckers to grow into their own tree. By the time the original trees have hit their life span they can be removed to allow the new trees to take over. This keeps your grove healthy and works with the aspen’s natural cycle.

Cotton

Poplars are dioecious which means there are male and female trees. Many varieties on the market are cuttings of known males so there is no cotton, but there will be pollen and male catkins. Some are sterile hybrids that also don’t produce cotton.

Common Ailments

As native trees, all the insects and diseases of poplars are right in our back yard. Keep your trees healthy by watering adequately, but not too much, and slow down on the fertilizer. They grow quickly enough on their own.

Diseases:

Sooty Mold – trunk gets a splotchy/moldy appearance. This is the result of aphids dropping honeydew onto leaves, branches, and the trunk. It can be unsightly but is harmless to the tree.

Leaf Spots – Marssonina Leaf Blight, Black Spot, and Septoria Leaf Spot are all common foliar diseases. Leaf cleanup is usually enough to suppress disease in mature plants. Young or newly transplanted trees may require treatment with fungicide. Keep sprinkler water off the leaves.

Cytospora Canker – Also called Valsa or Leucostoma. This fungal pathogen infects the cambium of trees and can cause significant canopy dieback and can girdle the tree if it gets into the trunk. There are no curative fungicides, cankers should be pruned out 8+ inches past the visible infection. Small trees can be treated during the following spring to prevent new cankers.

Insects:

Aphids – A common insect that feeds on the leaves. They drop honeydew which can be unsightly or cause molds to grow on decks, sidewalks, or on the tree trunk. Plant flowers that attract ladybugs or simply use a dormant oil in March prior to leaf emergence. See our handout for more information.

Leafminers – small insects that tunnel through the leaf structure. They are not considered to harm the health of the tree but can be an indicator of tree stress. Look for environmental stressors such as too much or too little water, as well as overfertilization. A spray on systemic (acephate) can be used for newly transplanted trees but is not necessary once established.

Poplar Borers – The larval stage of borers consumes the cambium and burrows extensive tunnels throughout the wood. This can allow heart rot which increases the likelihood the tree will fall. Stressed trees are more likely to be targeted. See our handout for more information.

Most poplars will freely hybridize with other species. However, there are a few species which are fairly stable and readily available in the nursery trade. This guide is to help distinguish some notable characteristics between them. Be aware you may find seedling hybrids growing naturally along streams and rivers throughout Montana.

Common Name	Latin Name	Size	Zone	Age (years)	Cotton	Notes
Quaking Aspen	P. tremuloides	40’ tall 30’ wide	2	50-60	None, some drop catkins	Tolerant to many soil conditions, grows quickly, suckers to form a grove
Swedish Columnar Aspen	P. tremula ‘Erecta’	35’ tall 6’ wide	2	50+	none	Very cold tolerant, columnar shape is easy to work into narrow garden spaces, doesn’t sucker as much as the regular aspen
Black Cottonwood (aka Balsam Poplar)	P. balsamifera  ssp. trichocarpa	30-100’ tall *<60’ in MT 25-30’ wide	2	60-200	Possible	Male and Female trees. Largest specimens are over 100’ in height and have a trunk over 6’ in diameter, does well at high elevations. Native to the Gallatin Valley.
Dakota Cottonwood (var. of plains cottonwood)	P. deltoides ‘Dakota’	75-100’ tall 50-75’ wide	3	70-100	None	While the regular Plains Cottonwood (P. deltoides) have male and female trees, ‘Dakota’ is a selection of male trees which are cotton-less. Prefers moist conditions but tolerates dry and saline soils
Lanceleaf Cottonwood	Populus. x acuminata	45’ tall 20-25’ wide	3	30-50	No cotton, Catkins can be quite large	Also called Lanceleaf Poplar. Hybrid between P. deltoides and P. angustifolia, prefers moisture, grows at higher elevations, up to 8,500 ft
Narrowleaf Cottonwood	P. angustifolia	60’ tall 30-40’ wide	3	30-50	Possible	Also called Narrowleaf Poplar, prefers moist conditions and well drained soils (young trees are not drought tolerant), suckering, grows at altitudes up to about 8,000 ft. Native to the Madison and Shields River Valleys
Brooks Poplar	Populus. x ‘Brooks’  (Originally P. deltoides)	50’ tall 35’ wide	2	15-30	None	Tolerates short periods of low moisture, tolerates some shade, tolerates late and early frosts. Performs better than other poplars in dry climate
Highland Poplar	Populus. x ‘Highland’	45-50’ tall 20-25’ wide	3	30-50	None	Light colored bark like Lanceleaf cottonwood, more disease resistant than other species, aggressive roots