Chapter 107 Malus species
107.1 Crabapples
A large crabapple with hundreds of newly formed green crabapples. Link to original image.
Crabapples are a traditional bonsai species in Japan. We are fortunate in that there are several native North American species available for experimentation.
| Scientific Name | Common Name | Flowers | Fruit | Notes |
|---|---|---|---|---|
| Malus cerasifera | Nagasaki crabapple | white to pink | 1/3”, bright red | widely used in Japan. May be a hybrid of M. baccata (Siberian c.) and M. prunifolia (Chinese plumleaf c.) |
| Malus halliana | Hall’s crabapple | colorflowers | bright red | widely used in Japan, native to East Asia |
| Malus angustifolia | Southern crabapple | single pink, fragrant | yellow-green | susceptible to fireblight; N. Am. native |
| Malus coronaria | Sweet crabapple | single white | yellow-green | resistant to fireblight; N. Am. native |
| Malus sargentii | Sargent crabapple | profuse single white, fragrant | 1/4”, red | leaves are yellow in fall, contrasting with long-lasting fruits. Native to Japan |
| Malus ‘Prairie Fire’ | deep pink flowers | 1/2”, dark red | high disease resistance | |
| Malus ‘Robinson’ | deep pink | 3/8”, bright red | very high disease resistance |
107.2 Soil: Moist Deciduous Mix
Ratio: 4 parts bark, 1 part grit
Add-ins: dolomitic limestone (~5 lbs/yd), Tree-Tone (15 lbs/yd)
pH: ~6.5 (slightly below neutral)
Moisture: Average
107.3 Light
Routine: Half-day to full sun.
Summer: Mid-day shade can reduce leaf burn, but some trees will not need it.
107.4 Cultivation Notes
Crabapples tend to bloom in the middle third of the spring. The exact time they bloom varies by cultivar, and is influenced by light and air temperature. Generally though, trees kept together will bloom in the same sequence each year.
New shoots extend quickly during the cooler days of spring, then slow down once daytime temperatures stay above 70oF consistently.
107.4.1 Potting & Root Pruning
Repot in early spring. They prefer deeper containers with consistent moisture. I do not have enough personal experience to know how much of the roots can be removed on larger trees, but crabapples used as grafting rootstock will regenerate from nearly bare taproots. I expect they are quite tolerant.
107.4.1.1 Top & Branch Management
Like apples, crabapple trees can tolerate severe pruning. However using an aggressive clip and grow approach more than once will create a lot of scars that will not callus over. The better approach is to grow the tree out once in open ground to build the trunk diameter, cut it back once, then selectively build the branches using emerging buds as they appear.
The best time to prune Robinson and Prairie Fire cultivars is mid-winter when the trees are dormant, or at the end of spring before the summer buds arrive. Robinson crabapples respond especially well to pruning.
Heavy pruning: remove large branches from late fall to mid-winter. Remove dead, dying or damaged branches, and any crossing branches. Thin out crowded areas that prevent good airflow.
Fine pruning: to encourage flower production, trim to shape right after flowering, then let all shoots run unchecked til late summer. At that time, cut the shoots back to 2-3 buds, and remove any that are not wanted.
Pinch off any leafy shoots the grow near the base anytime they appear. These rob the tree of nutrients and moisture, and may be from the grafting rootstock.
Leaf pruning: do not leaf prune a crabapple. It reduces the number and quality of the flowers.
107.4.2 Feeding
Fertilize in spring, after new leaves have begun to emerge.
Crabapples are heavy feeders. They also prefer a more balanced fertilizer than is typically used for containerized trees; 3-3-3 or 5-5-5 is best. Espoma Garden-Tone (3-4-4) or Berry-Tone (4-3-4) are the closest organic options to this ratio. Miracle-Grow Soluble Tomato Food is formulated as 18-18-21, so has a reasonable nutrient balance, but should be applied at 1/4 strength, and preferably 1/5 normal strength.
Avoid 10-10-10 granules; they are too strong for use in pots.
107.4.3 Pests & Problems
Like other members of the rose family, crabapples are susceptible to many insect pests and disease. Check your trees frequently for mites or aphids all season. As the summer heats up, watch out for caterpillars, Japanese beetles, and other leaf-eating insects.
If you have junipers or cedars in your bonsai collection (or within a mile of your location), be on the lookout for cedar apple rust. This disease is extremely common in Piedmont NC because of the number of cedars growing wild. The spores create unsightly dead spots on the crabapple leaves, and severe outbreaks can defoliate a tree.
One of the most devastating diseases of crabapples is fireblight, which is endemic to our area. The severity varies each year based on the spring weather. Read the essay on fireblight for more details. Watch crabapples closely for branches that suddenly wilt and blacken as if burned. Cut these branches off immediately, and sterilize your pruners afterwards with 70% alcohol or 5% bleach. Dispose of the clippings in a plastic bag in the garbage. Some cultivars seem more resistant, while others are likely to show signs every year. A few cultivars have no resistance at all, and fireblight will destroy the entire tree. Once fireblight kills the main branches back to the trunk, the tree cannot be salvaged.
Chemical Warnings
Do not spray crabapples with chemicals while they are in bloom. Even mild organics can be toxic to native bees, which already struggle to find sufficient nectar early in the season. If you plan to put your crabapples on a routine spray program, wait until after the blooming period ends to start.
A crabapple just starting to change to fall colors. Link to original image.
107.4.4 Winter Storage
Store in mulch outdoors. Crabapples are very cold-hardy; the greater enemy is warmth. Crabapples need to be shaded so buds do not break in a mid-winter warm spell.
107.5 Propagation Notes
Container stock is available in early spring at most nurseries. Crabapple cultivars must be propagated via cuttings and grafting. They will not grow true to form from seed.
107.6 Artistic & Styling Notes
Crabapples often develop rotten wood in the center of the trunk. Rather than hide it, carve it out and use it as a feature. Be sure to treat carved areas annually with a preservative like boiled linseed oil.
107.7 Additional Information
107.7.1 Natural History
107.7.2 In Cultivation
Beside the Japanese cultivars, two ornamental crabapples that are widely grown in the U.S. would make eye-catching bonsai. The variety known as ‘Robinson’ is famous for its eye catching pink flowers that bloom in early spring and red-purple fruit. Robinson attracts butterflies, and is pest and disease resistant. They prefer full sun, but can also tolerate partial sun. Try to provide at least 4 hours of direct sunlight daily. These trees prefer soil that is well-drained and slightly acidic. Shoot for a pH closer to 6.0 than 6.5.
The other cultivar of note is the ‘Prairie Fire’ crabapple. It has some of the most intensely pink to red flowers of any crabapple currently available. It also prefers well-drained soil that is slightly more acidic.