Empress trees, sometimes called princess trees, are known for their fragrant late-spring purple flowers. In addition to the lovely blooms, they have very large, fuzzy leaves to more than a foot wide. Empress trees can be extremely fast growers (depending on growing conditions)-but because of their fast growth, their wood is weak and not as weather-tolerant as many other trees.
- Common name: Empress tree
- Botanical name: Paulownia tomentosa
- Zones: 5 to 8
- Size: To 40 feet tall and wide
- From: Areas of Asia
- Family: Scrophulariaceae (foxglove family)
- Sun: Full sun
- Soil: Moist, but well-drained soil is best. The trees do tolerate a range of soil conditions, however.
- Moisture: Water during times of drought.
- Zones: 5 to 8
- Mulch: A 2- to 3-inch-thick layer of organic mulch around the base of the tree is quite helpful in reducing competition from weeds and conserving moisture. Avoid placing mulch right up against the tree's trunk---leaving a gap of at least 4 inches is best.
- Pruning: Prune in summer after blooming.
- Fertilizer: In most soils, fertilizer is unnecessary.
- Seed: Sow seed at temperatures around 50F; seeds may take 6 months or more to germinate. Also: If the trees self-seed, pot up the seedlings and grow them. Otherwise harvest the seed as soon as it is mature and sow in a cold frame or sheltered spot in the garden.
- Aphids: If plants are attacked by large numbers of very small insects at the tips of the new growth, it is probably the work of aphids. Try repeatedly spraying them off plants with a stream of water from the garden hose; encourage beneficial insects; apply insecticidal soap or horticultural oil.
- Canker: Forms dark water-soaked cankers on the bark and branches of the tree. The cankers can spread, becoming larger. To deter the disease, prune off any infected branches, dipping your pruning tool in a bleach or alcohol solution between cuts.
- Powdery mildew: Powdery mildew appears in mid- to late summer and looks like affected leaves have a grayish powdery covering on them. The leaves then drop off. To deter the disease, prune the plant to keep good air flow and avoid wetting the foliage in afternoons and evenings.
- This tree is considered potentially invasive in some parts of the country and may be banned in some areas. Check local restrictions before planting.
- The wood is considered desirable and has many uses, especially in the Far East.
- Empress trees tend to tolerate air pollution.
- It has a tendency to self-seed---these seedlings can get to be weedy.
- In the northern areas of their growing range, the flower buds may freeze in particularly cold winters. These winters can also cause the plants to exhibit some winter dieback.
- The growth rate depends on several factors, including the health of the tree and how well it's suited to the site. Trees can grow from very slowly to very quickly.
- Paulownia fortunei: This species is hardy to Zone 6, grows to 30 feet tall, and creamy-purple springtime flowers.
- Paulownia kawakamii: This species is hardy to Zone 6, grows to 35 feet tall, and purple-striped, white springtime flowers.