Don't overlook the stalwart chaste tree

Why is it that when we are looking for great plants for our gardens, we tend to overlook the old stalwarts that have served so well? Sometimes I think that if a plant doesn't present much of a challenge, we quickly lose interest. Vitex agnus-castus is a plant that certainly has given its all, but for some reason it has lost favor with today's designers and growers.

The long and the short of Vitex agnus-castus is supreme cultural adaptability, vigorous growth, clean foliage and a fabulous floral display from midsummer to frost. Not a plant for the weak of heart, this baby is a strong grower to say the least. It is a heavily multitrunked plant which, if cut to the ground in winter, will produce a densely branched specimen up to 8 feet tall. If not cut back, it can get a tad on the unkempt side. It can be pruned up to a small tree but in my opinion it is much better suited as a shrub.

Palmately compound, opposite leaves maintain a rich, lustrous green all season with little in the way of insect or disease damage. Leaves are covered on the undersides with soft, silvery-gray pubescence. Fall foliage color consists of a frost-induced crispy gray; not the strongest season for the species. Luxurious lavender-blue flowers of variety latifolia are produced on old or new growth and are borne in tight spikes arranged in terminal panicles up to 8-10 inches long. In Kentucky, the display begins in early July and a reasonable smattering of blue could still be seen on Bernheim's plants as late as Halloween. The flowers are borne heavily July through September and sparsely thereafter. Outstanding fragrance has been attributed to the flowers, but I fail to pick up anything; but then again, I don't get much fragrance out of Leonard Messel magnolia either!

Butterflies don't seem to have a problem with the flowers, though. On a late July afternoon, I counted no fewer than 30, working flower to flower on a single plant. In general, considering the overall presentation of the plant, one can almost describe it as a Buddleia without the mite problems.

Chaste culture

As for culture, chaste tree will work fine in almost any reasonable soil. The heavy Kentucky clay at Bernheim is no match for this beast. It grows along, seemingly with no notice of the compacted mess surrounding its roots. While it is relatively drought tolerant, the plant does best with ample water supply. Soil pH does not even seem to enter the equation. I have seen the plant performing equally well on soils ranging from 5.2 to 7.5.

As to cold tolerance, the plant is best in USDA Hardiness Zones 6 and south. In Zone 6, there will be occasional heavy winter damage which, of course, is not a problem with annual cut-back treatment. The plant can perform admirably in Zone 5 if cut back in late fall and mulched heavily for the winter. While latifolia certainly seems more vigorous than the species as listed in most references, I'm not so sure about the supposed increased cold tolerance. As for heat tolerance, chaste tree does not only survive the heat of Zones 7 and 8, it actually seems to embrace it. Water amply, fertilize modestly and you simply can't miss.

SPECIFICS:
Name: Vitex agnus-castus
Common name: Chaste tree, Indian spice, sage tree, hemp tree
Family: Verbenaceae
Hardiness: USDA Hardiness Zone 6; 5 if cut back and mulched
Form: Can be grown as a small tree to about 8 feet, or pruned as a shrub
Flower color: Variety latifolia is blue; cultivars 'Alba' and 'Silver Spire' are white, 'Rosea' is pink.
Landscape value: Splendid small tree that flowers from mid-summer to fall, adapts to many soils, has few pests, thrives in hot climates, and attracts butterflies.

-- Paul Cappiello, Bernheim Arboretum & Research Forest, Clermont, Ky.

© 1999 Branch-Smith Publishing