Thornless hawthorn looks a bit like a crabapple (to which it’s related). It has shiny dark green leaves, clusters of pink-blushed white flowers, and red fruits at the end of the season. In autumn, the foliage takes on a decidedly red tint. The fruits, which resemble crabapples, are also attractive to wildlife. Unlike other hawthorns, this one does not bear the wicked, 2- to 3-inch curved thorns hawthorns are known for.
- Common name: Thornless hawthorn
- Botanical name: Crataegus crus-galli var. inermis
- Zones: 4 to 7
- Size: To 25 feet tall and 30 feet wide
- From: Areas of North America
- Family: Rosaceae (rose family)
- Sun: Full sun.
- Soil: Moist, but well-drained soil is best, though hawthorns can tolerate various conditions. Avoid especially heavy clay soils or very compacted soils, however.
- Moisture: The trees are relatively drought resistant. Watering during times of drought will keep up the tree’s appearance. To avoid many disease problems, don’t plant in a site that’s wet.
- Mulch: Lay a 2- to 3-inch-deep layer of mulch over the soil around the tree. Avoid laying the mulch directly up against the tree’s trunk—leave a several-inch-wide gap to prevent disease problems.
- Pruning: Prune in winter. Keeping the centre of the plant pruned well to encourage good airflow can prevent many disease problems.
- Fertiliser: Additional fertiliser is rarely necessary in average soils.
- Seed: Collect ripe fruits and remove the seeds in autumn once the fruits fallen from the tree. Soak the seeds in warm water before planting. Plant them in a sheltered spot in the garden or in a cold frame.
- Athracnose: If the leaves look scorched and spotted, the cause may be anthracnose. The spots may be grey, tan, or dark brown; dry or slimy. To deter the disease, prune off any infected branches, dipping your pruning tool in a bleach or alcohol solution between cuts. Prune some of the inner branches to keep good airflow in the tree’s centre.
- Aphids: If plants are attacked by large numbers of very small insects at the tips of the new growth, it’s 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.
- Cedar-hawthorn rust: Usually looks like leaf spotting that is followed by small masses of rusty-colored powder on the leaves. Infected leaves die by the end of the season. To deter it, avoid getting the foliage wet; make sure there is good air circulation around plants. The disease requires junipers to complete its life cycle; avoid planting hawthorns near junipers.
- Fire blight: In spring, this disease causes branches and leaves to shrivel, looking as though they were damaged in a fire. The bark may also be darkly coloured. Cankers may form that can ooze out liquid. To deter this disease, control insects that can help spread the disease and don’t plant other susceptible plants—other plants in the rose family—nearby.
- Leaf spot: In summer or autumn, the leaves become spotted yellowish or with darker coloured spots. Each spot often has concentric rings around it, forming something of a bull’s-eye pattern. To deter this disease, prune the tree to ensure good airflow. Avoid wetting the foliage in afternoons and evenings.
- Leaf miners: If the leaves look like they have tunnels going right through the middle of them, it is probably the work of leaf miners. To deter this insect pest, destroy affected leaves and mulch around the base of the plants to keep the larva from burrowing into the soil to pupate. Leaf miner damage is more cosmetic than harmful to the plant.
- Powdery mildew: Powdery mildew appears in mid- to late summer and looks like affected leaves have a greyish 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.
- Crataegus crus-galli var. inermis ‘Crusader’. This cultivar grows smaller than the species and has orange-tinted leaves in autumn. It’s also more disease resistant.
- Crataegus crus-galli. This form has thorns and isn’t considered as desirable as the variety inermis.