Crab Apples and their Characteristics
Crab apples or wild apples belong to the Malus genus of about 50 species of small apple shrubs or small deciduous apples. Crabapple trees can grow up to a height between 13 and 39 feet. It is a flowering tree that blooms followed by the fruits that start coming out. Cross-pollination usually occurs between trees carried by insects, particularly bees, because the flowers carry both nectar and pollen. Crab apples cannot self-pollinate.
Crab apples are more popular as ornamental trees than fruit bearing trees, providing colorful blossoms and fruits for gardens in homes in the Northern Hemisphere especially during the autumn and spring. In some commercial apple orchards, crab apple trees are planted together with other commercial apple trees to serve as rootstocks to give additional hardiness to the commercial apple tree.
Unlike their sweeter apple fruit counterparts, crab apples are smaller and sour tasting, the sourness due to the malic acid unique to this genus. In some countries in Southeast Asia, the crab apple is valued as a sour condiment or sometimes eaten with chili pepper and salt or shrimp paste. In popular culture, the tree is very much liked for making bonsai plants,
Varieties of Crab Apples
With more than 50 varieties of crab apple trees in the Malus genus alone, we will simply list down the common varieties that are planted as garden ornamental trees.
Malus ‘Molten Lava’. A highly rated variety with white flowers, yellow-orange fruits, and can grow up to 10 feet. It has a weeping-spreading form for much of the year and never looks mediocre. Fruits and yellowing fall foliage provide a fiery cascading image. After the fruits all fall off, the remaining pedicels provide an attractive feathery winter effect that complements the elegant branching spreading form and structure.
M. ‘Red Jade’. This variety has white flowers, red fruits, and grows up to 10 feet. It gives off an element of great strength and is attractive in its spreading habit, providing nice foliage to look at through the year, especially in winter. It has an impressive blossom and fruit display. Strap-like leaves and twisting of petioles are characteristic of this variety.
M. ‘Mary Potter’. This variety has white flowers, red fruit, and grows to a height of up to 10 to 15 feet. It is very attractive through the summer months due to the pleasing spreading growth form and foliage. Exfoliating trunk bark is an intriguing feature.
M. ‘White Cascade’. This one has white flowers, small yellow fruits, and grows up to 10 to 15 feet in height. Exquisite flower display with waterfalls of cascading blossom covered branches, this variety provides a gorgeous presentation from early to mid summer due to its attractive weeping form.
M. sargentii. This small spreading variety has white flowers, red fruits, and grows up to a height of 10 feet. Its attractive low-spreading growth habit is an excellent feature, especially as the plant ages. Fruits tend to shrivel early in fall, diminishing its winter impact. Its close cousin, M. sargentii ‘Rosea,’ differs from the species in having rose-pink buds.
M. ‘Red Jewel’. A variety with nice white flowers, cherry red fruit, and can grow up to a height of 10 to 15 feet. Attractive, persistent red fruits are outstanding, complementing its small, delicate growth form. The plant is most terrific to look at through the fall and winter months.
Large Rounded Foliage
M. ‘Donald Wyman’. This is a highly rated variety of crab apple with white flowers, bright red fruits, and grows up to 20 feet. Lustrous green foliage, good overall growth habit, and outstanding small glossy fruits make this tree exceptionally beautiful. Its alternate flowering pattern results in a sort of sparse or off-bloom, though this selection typically has outstanding blooms.
M. ‘Sugar Tyme’. This variety has white flowers, brilliant red fruits, and grows up to 15 to 18 feet. It contains marvelous fruit and flower displays. Foliage remains clean and is an excellent all-purpose tree due to its captivating fruit display which begins in mid-fall and goes on through the winter.
M. baccata ‘Jackii’. This variety has white flowers, maroon-red fruits, and can grow to a height of up to 40 feet. Its glossy, large, disease-free, deep green leaves are an exceptional ornamental feature. It has a handsome overall form and structure. However, its fruit is somewhat sparse, but shiny and in attractive clusters that become soft in November. Its large form is rendered mediocre throughout winter months.
M. ‘Bob White’. This variety has white flowers, yellow fruits, and can grow up to 20 feet. Its outstanding feature from November through February is persistent, small, firm yellow-gold fruits maturing by January into orange-gold color. Foliage is relatively clean and only mediocre during the spring and summer months.
M. ‘Sentinel’. This one has white with pink tinged flowers, red fruits, and will grow up to a height of 15 to 20 feet. It has a vase-shaped upright habit and pink buds opening to tinged white flowers that always look sensational. Persistent fruits through the winter are nice but can detract during spring and early summer until they fall off.
Unique Growth Form
M. ‘Strawberry Parfait’. This unique variety has pink flowers and fruits start yellow with increasing red blush. Its unusual erratic upright-spreading growth habit is one of best features and produces good firm fruits into the winter. Foliage is striking as it develops along the upright stems in the spring. However, its unusual shape may not be for every gardener and for every landscape.
Are Crab Apples Edible?
As mentioned before, because of its sour and pithy taste, crab apples aren’t eaten like you would standard apple fruits. They can be eaten in small quantities since eating too much will give you a sore stomach, which is why people who eat them in Southeast Asia neutralize the sourness using chili pepper, salt, or fish paste. You can use some slightly mellower larger crabapple varieties for jam making. Most varieties of crab apples can also be made into traditional crab apple jelly, spiced crab apple preserves, and pectin for jam. You don’t need to be added pectin when you make jams or jellies with crab apples because the fruit has plenty of natural pectin all on their own.
Take note that the seeds of crab apple trees contain a form of cyanide called cyanogenic glycosides. Cyanide is a toxic and potentially fatal poison. However, despite the presence of cyanide in the seeds, most people don’t eat the core anyway. Even when Apple seeds are ingested, they usually pass through the gut without being broken down. You would have to eat lots of crabapple seeds and grind or chew them up for the cyanide to take effect.
How to Care for Crab Apples
Flowering crab apples are adaptable but prefer thriving in rich loam type soil. This is a combination of clay, silt, and sand. But regardless of soil type, good drainage is a must for the tree’s health. Crab apples grow best in a moist, slightly acidic soil with a pH of 5.0 to 6.5. Excessively moist areas where the water stays stagnant should be avoided. On the other hand, relatively dry soil can be tolerated by crab apples if plant stresses are minimized during the first year after transplanting.
Plant stress is evidenced by unhealthy appearances such as leaf scorch and poor leaf color and is a response to unfavorable environmental conditions. For instance, drought stress can be due to a lack of water coming from rainfall or manual watering. Water is essential for the plant’s general functions, but, too much water or over-watering will cause a persistent saturation of the roots, can lead to root rot and eventual plant death. Other plant stresses include too much shade, insect infestation, infectious diseases, and physical damage from lawnmowers, weed-eaters, animals, and from children damaging the tree.
A full sun exposure of 8 to 12 hours to direct the sun is required for optimal development of fruits and flowers. Most flowering crab apples are hardy and can endure the colder temperature extremes of even the weather from the east coast.
Fertilizing. When crab apples are planted in a soil of average fertility and provided moderate amounts of organic matter, they need little additional fertilizer the first year. However, if annual growth is less than five to six inches or leaves are small or pale green, then fertilizer is needed. You can also use a little compost mixed into the soil and put a little mulch for soil protection when the tree is still small and growing.
Watering and Irrigation. If the crab apple tree is well established after the first year, little additional watering is needed unless drought conditions prevail. In a drought situation, it is necessary to water thoroughly and deeply every two or three weeks. Depending on the soil type and drought severity, two to six inches of water should be applied at each watering interval. In truth, if crab apples are not watered during periods of drought they will not collapse and die. However, the trees will use most of their carbohydrates to merely exist and survive. As a result, by the next year, the tree will not have a flower and fruit display due to the diminished nutrients and needs to replenish itself.
Pruning and Repotting Guide. Crab apples don’t take up much space even if they can be huge, sprawling trees or small garden trees depending on the rootstock chosen. When you are considering a crab apple for your small garden, look for one grafted into dwarf rootstock or start pruning from the top as soon as it reaches your desired height. Crab apples on dwarf rootstock don’t take up much space. Although these can still grow up to 12 feet tall, they can be easily managed in a small garden by doing judicious pruning.
But in general, crab apples require little pruning. Rapidly growing shoots from branches called water sprouts, rapidly growing shoots from roots or base of a tree called suckers, dead, diseased, damaged, and crossing branches should be removed. Occasional pruning is necessary to open the center of the plant to sunlight and air movement or to remove a wayward branch. When pruning is done it should be completed before early June. By the middle of June to early July, flower buds for the next season will begin to form in crab apples. Pruning after July will reduce floral display and fruit growth in the following year.
Propagation Guide. Tree health and vigor depends upon proper site selection and preparation. Before planting, have the soil tested to assure proper pH and nutrient levels. If necessary, make the necessary adjustments to the soil before planting.
Flowering crab apples may be planted almost any time of the year. Balled and burlap stock and containerized trees can be planted any time after spring frosts end through fall up until about three weeks before the ground starts to freeze. However, bare root trees should only be planted in the spring. Bare root trees will become too stressed if planting is delayed past early spring. Every effort should be made to keep roots or the root ball from drying out before planting. For bare root trees, the planting hole should be dug wide and deep enough to allow for the natural extension of the root system. None of the roots should be cramped or bent to fit into the hole. This can result in strangling the roots that will slowly kill the tree. Damaged roots must be pruned just above the break or damaged area prior to planting.
For containerized or balled and burlap trees, a saucer-shaped hole should be dug. The overall size should be at least two times wider than the root ball diameter. The center depth of the saucer should be the exact height of the root ball. This allows the burlap to be untied and placed down into the hole at planting. Make sure all strings holding the burlap at the base of the trunk are removed or these can damage or eventually kill the tree in a few years.
Containerized plants should be removed from the pots just prior to planting. Using a small, sharp knife, slice one inch deep into the compacted root mass, from top to bottom, in at least three different areas. This will help prevent the formation of girdling or strangling roots. Most flowering crab apples can be grafted to other apple tree root systems – rootstocks – and can be planted at the original depth they were in the nursery or slightly higher at around 1 to 2 inches deep. Long term root decline can happen if trees are transplanted too deep. When tree roots are buried deeper than originally grown, the tree can languish for years, resulting in lackluster appearance and health, and the tree may eventually die.
Backfill the planting holes with a 50-50 mixture of the original soil and organic matter such as leaf humus, compost, peat moss, or even a few mulches. Do not pack backfill around the root ball. Instead, use water to help settle the soil around the roots when the hole is three-quarters full. When the water has drained, backfill the hole completely and water again. Place a thin layer of mulch, no more than two inches deep, around the tree to help reduce water loss. Turfgrasses will compete with the young tree for water and nutrients so keep all types of turfgrasses away from the rooting area of the planted tree to provide optimal conditions for tree growth, development, and survival. The young tree will need about one inch of water, rain or manual watering, per week. During the first year, this weekly watering is subsequently crucial for tree development.
Common Problems (Pests and Diseases) and How to Cure Them
Many crab apples are disease resistant or tolerant even in their stages of growth or flowering. Disease resistance involves genetic resistance to infection by disease-causing organisms. Disease tolerance implies the plant may be affected by certain diseases but is not directly significant or dangerous to the plant.
Unfortunately, few crab apple varieties possess all desirable characteristics of exquisite flowers, fruit, foliage, growth habit, and disease resistance. This does not mean that other cultivars should not be used. Many crab apples are slightly susceptible to certain diseases and yet have great resistance, a seeming paradigm for this plant. By accepting and understanding their limitations, these plants are perfectly acceptable in most landscape situations regardless of the weather.
This fungal disease first affects emerging leaves in the spring during moist conditions, and then moves to infect the fruit. Scab causes dark, leathery spots with a corky appearance on the fruit. On leaves, scab infections first appear in May or early June as olive-green or oil-soaked spots. On more mature trees, the leaf infections appear as black, velvety spots that are slightly raised. As the disease develops, leaves turn yellow and drop prematurely. If the tree is heavily infected, defoliation can occur by early summer. Control can be achieved by one of two ways: Remove the trees that are highly susceptible and select other less susceptible disease-resistant crab apples. On the other hand, try applying fungicides as leaves begin to emerge, at two weeks and again four weeks after the first application.
Frog-Eye Leaf Spot
Symptoms of this fungal disease are typically small, dark brown spots that are dead leaf tissue that is outlined by a thick, dark purple circle. Frog-eye leaf spot is found commonly on many flowering crab apples and its effect is usually heavy defoliation, but still depending on the tree’s susceptibility to this fungus. The best course of action is to select crabapple varieties that are resistant or tolerant to this disease.
This disease is caused by a devastating bacterium called Erwinia amylovora. Symptoms are usually new terminal shoots that start to die off in late spring or early summer. These shoots appear to be scorched by fire. The leaves remain attached to the blighted shoot which develops a characteristic curvature at the tip, commonly called a “shepherd’s crook.” The disease often progresses down through the shoot and forms a canker in the older tissue. These cankers are typically sunken areas that are dark brown to purplish in color. An orange or amber gum may ooze from these infected parts. As the bark dies, the area becomes slightly depressed. To be able to control fireblight, first, select plants that are genetically resistant to fireblight. If that is not an option, then sanitation, removal, and disposing of blighted branches and shoots are the best alternatives.
Insects and Other Pests
Flowering crab apples are can be relatively undamaged by most insects. Although they are frequented by various types of caterpillars, leafhoppers, leafrollers, leaf-miners, and Japanese beetles, these pests rarely cause significant damage to the tree. Most nest forming caterpillars are easily pruned out or removed with a gloved hand. Japanese beetles and other pests are easily controlled with insecticides. Control may be warranted in young trees if one-third to one-half of the foliage is affected. Remember that when a tree is flowering, this attracts a lot of insects, and the same may be said when the tree is bearing fruit.
Things to Keep in Mind When Growing Crab Apples
Crab apples may present some danger for roving pets, especially dogs. A pet that consumes a few crab apples may show signs of discomfort. In serious cases, if an animal eats lots of crab apples, including stems, leaves, and seeds, they could show signs of cyanide poisoning. Dogs rarely eat enough plant matter to cause a real problem, but plant eaters like horses, sheep, cows, and goats may eat crab apples in large enough quantities to trigger some toxic effects.
To minimize the danger, you can simply stop growing the tree or prevent any animal to approach the tree. Or you can remove the core, stem, leaves and any seeds from the fruit before use. These are the only parts with the toxic cyanogenic glycosides. The tart flesh of crab apples does not contain the poisonous substance.