The name of catalpa tree derives from the Indian language, meaning “elephant`s ears”. These are attractive, mostly deciduous (sometime evergreen) trees with broadly rounded crown. The leaves are heart-shaped and large with long petioles. The showy bell-shaped flowers up to 7 cm long, held in large terminal sprays, are white or cream, with lower lips splashed with purple blotches and spots. Long (up to 40cm) fruits, which resemble bean pods, open to release quantities of light winged seeds. The tree retains these curious seed pods well into winter, which only increases its ornamental value.
Southern catalpa (Catalpa bignonioides Walt.) grows to 15-20 m tall, with wide-spread branches and a rounded crown. The bark is light brown. Leaves of this species, resembling those of lilacs, if only larger and wider, are light green with downy undersides. Flowers are up to 5 cm long, white with purple blotches and two yellow strips, held in broad frothy panicles, which carry on flowering for about 20 days.
In spring catalpas start breaking into new growth in mid-May, stopping in August. Leaves drop after the first frosts, without giving any colourful autumn displays. It is a fast-growing tree, sometimes at a rate of half a metre in a growing season. However, sometimes all this growth dies down during a particularly cold winter. It is also susceptible to draught, so watering young plants during a prolonged dry spell is essential. Catalpas associate well with magnolias and oaks, however, they dislike being planted in exposed locations, where winds tear their leaves to shreds.
The cultivar `Aurea` is grown for its lime-green foliage, while yellow leaves of `Koehnei` are patterned with green veining and a dark spot in the middle of the leave. `Nana` is a very compact and rounded cultivar, and is often top-grafted on a tall stem, which makes it suitable for planting in knot gardens.
The leaves of Northern catalpa (Catalpa speciosa Warder et Engelm.) are narrower that those of southern catalpa, and break into growth later in the spring. Leaves are green, shiny and downy on the undersides. Fragrant, frilly flowers are up to 7 cm long are creamy white, with lower lip splashed in purple and decorated with two yellow strips. Flowers are held in 15-20 cm long panicles and carry on flowering for about 20 days. Long (up to 45 cm) seed pods mature by the end of the summer.
Catalpas are sun-loving trees, which dislike being planted in a waterlogged site or in locations, where the water table is high. Trees grow best when planted in moist, well-draining soil. Planting should be done in spring. Seeds fully ripen only in warm and long autumn without early frosts. Propagate catalpas by seeds, cuttings or layering.
The foliage of northern catalpa `Pulverulenta` is mottled white or cream.
The leaves of Chinese catalpa (Catalpa ovata) resemble those of the tulip tree. Its flowers, which appear in mid-July, are scarce. The tree sets seeds, but they do not fully ripen. Seeds pods are shorter than those of the catalpas of other species.
Plant catalpas in a sunny and sheltered location, since the luxurious leaves suffer if exposed to severe wind. When planting an alley of trees, space them at 4-5 m intervals. If you plant in a poor soil, dig a planting hole 0.8-1.2 m deep, fill it with mixture of well-rotted compost, loam, sand and peat (3:2:1:2), and add 5 to 8 kg of wood coal ashes. Catalpas dislike growing in acid soil, with pH 6.5-7.5 being optimum.
Water thoroughly, once a week, at a rate of 15-20 l of water per planted tree. When the tree breaks dormacy in spring, remove damaged or dead branches. If trees are planted in autumn, mulch around them thickly with peat, or alternatively, insulate them with some horticultural fleece and straw.
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