The species is not without merit; it is somewhat attractive, mostly due to the tomentose underside of its leaves, which along with its bark, gives the tree its name, white poplar. (Tomentose means a leaf covered with dense hairs!) The leaves appear white to be white on the bottom. It can be useful as an erosion deterrent in hilly areas near water, especially near coastal areas that might be affected by salt water, because the species has a high salt tolerance. When planning to use the white people, it is important to consider the ecological risks and any local or state ordinances regarding its invasive status when deciding to plant or consider the species in a landscape design. Other trees may serve the same function and offer the same aesthetic value, if not more than the white poplar.
Light
The white poplar does best in full sun but will also take to partial shade. Placing it in an area with less sun may slow the white poplar’s growth leading to fewer issues with branches growing overly fast with the species’ notoriously brittle wood and suffering wind and storm damage. This is a win-win, which will also benefit less pruning and possibly less maintenance and repair and damage costs if an unfortunate issue arises with tree damage.
Soil
What makes the white poplar so troubling to ecologists is its ability to adapt to a wide range of conditions and grow almost anywhere. Normally this would be a favorable trait, but when a species outcompetes or hybridizes with native species and populations, that becomes troublesome. This is the case in many areas with the white poplar. It does very well in areas where the soil is moist, rich, wet, or average. It can also thrive in sandy and has a high tolerance to salt, making it an excellent candidate to place in coastal areas where shade may be needed and dunes need to be reinforced. The white poplar also has a wide range of pH soil adaptability, thriving on soil that is slightly acidic to tolerating soil that is alkaline If you are not sure how to find out your soil pH it is easy to do.
Water
Like soil conditions, the white poplar is extremely adaptable to all water conditions once it has reached maturity. While it prefers moist and wet conditions and takes well to a good amount of irrigation, it is incredibly drought tolerant once established. This trait is another reason the tree is considered a risk; it can adapt and out-compete natives once introduced to an ecosystem. Ideally, planting a sterile cultivar is the best, and this will require some supplemental irrigation until the tree is established. Using the common guidelines of ten gallons per inch of trunk caliper diameter per week, one or two watering seasons should be plenty. After that, let nature takes control, and everything should work out just fine.
Temperature and Humidity
Originally from a swatch of the globe north of the equator that runs from Western Europe to Central Asia, the white poplar favors cool winters and warm summers that do not receive an abundance of humid weather. Again, this weather aligns perfectly with the weather in the United States, where the tree was introduced, which is why it thrived and spread so well when it was first introduced in America in 1784. It will thrive in USDA Zones 3 through 8.
Fertilizer
With its tendency to grow fast and brittle wood, the last thing that is needed is to accelerate the growth of the white poplar any faster. For this reason, providing it with supplemental fertilizer is not advised unless there are severe soil deficiencies that are causing the tree to suffer adverse effects. It should be determined if the soil is the issue with a simple test before fertilizer is applied; most likely, any issues with the tree are caused by a pathogen or insect and not a lack of nutrients.
Types of White Poplar
The wild type of Populus alba is not recommended for horticultural use for many reasons and is only for open spaces because of its weak wood, large size, and shallow, suckering roots. The species is known to hybridize with many other poplars, which produce trees that are just as unfavorable for horticultural use. In the nursery trade, two widely used selections have become available that are somewhat more attractive and less invasive as they are unable to reproduce sexually but can still produce clonally as is any other stand of poplar. The two cultivars most commercially available are:
Populus alba ‘Bolleana’ is a columnar form of the tree with a singular straight trunk. It is female, so it produces less mess and no pollen. Populus alba ‘pendula’ is a weeping white poplar with more attractive showy yellow foliage in the fall.
Pruning
Pruning will be the most important of all the care that can and will be given to a white poplar. White poplars are a short-lived species that are fast growing with especially brittle wood, known for wind and storm damage. To reduce wind exposure, regular pruning will need to be done starting in the spring, a full year after the tree has been planted. Pruning early in life is critical for establishing a good structure. The first step in ensuring that the tree is as strong as possible is eliminating any harsh crotches and intersections and establishing a singular leader or trunk. The tree will naturally have an oval crown, so it is best to make all cuts so that the branches establish a pattern away from the leader. Continue this yearly checking for dead, dying, or damaged branches. As mentioned, this is a fast-growing tree, so there will only be a few years before the work will head off the ground onto a ladder. At this point, it is a good idea to call in the pros, which means looking into a certified arborist who can do the work safely.
Propagating White Poplar
It is easy to propagate a white poplar by cutting, but it is highly recommended that you do not propagate this plant. Buying a selection from a nursery is the safest way to ensure that a selection you receive will be sterile and unable to reproduce sexually. The concern is not just ecological; in many states and municipalities, there are ordinances against the propagation, planting, selling, and transportation of white poplar plants. Be safe and check your local and state ordinance and your DEP and State Extension Service.
Common Pests & Plant Diseases
Among the most problematic insects that a white poplar can host is the poplar borer Cryptorhynchus apathy. The evident adults who are seen do some damage, chewing the bark of the tree, but the real culprit is the larvae of the species, which burrow through the trunk, creating channels and expelling a sign of their work, a material that looks like sawdust known as frass. These insects’ channels interfere with the flow of nutrients and water through the tree, eventually leading to its death. Sadly, removing the tree is usually the most cost-effective and safest treatment route. Solving the problem before any potential accidents are created with the poplar’s brittle branches after they die should be the biggest concern. The white poplar suffers from many diseases. It is prone to infection, and the best way to prevent a tree from getting sick is to give it good general care, but occasionally that does not work in all species. The most common disease seen in white poplar is canker and dieback, caused by a few different species of host fungi. Canker can disrupt water and nutrient flow, possibly leading to the tree’s death. If the affected tree suffers from the disease in more than half the trunk diameter, the tree’s survival is not good. Prune away diseased branches, remove severely diseased trees, and burn the wood to ensure the pathogen is not spread.
