An elusive summer perennial named hyssop

One of the things a gardener misses about the spring is the vibrant color of young leaves. The lime greens of certain hostas, deutzias and Japanese maples add accents of vitality so emblematic of April, a month that now feels distant in the sullen lushness of summer.

In northern gardens, these colors remain as strong echoes; in round-the-clock heat they are much fainter cries. A few, sited with just enough light or shade, remain strong. The hakone grass variety All Gold continues as a pleasing splash of chartreuse in my garden. Nearby, a stand of the giant hyssop Golden Jubilee glows a yellow green.

Now settled from their spring planting, the five hyssops are robust, upright and, at 4 feet and growing, twice the height they were six weeks ago. The growth spurt (no staking required) has been capped with the emergence of fluffy purple-blue flowers. They will draw bees and butterflies over the next eight weeks. I'd like to put the planting of this perfect summer perennial down to my perspicacity, but in truth it was a totally unplanned triumph.

When I asked my nursery friend Bill to find me some hyssops, or agastaches, I thought he would divine that I had in mind the versions that offer a fragrant, colorful and durable display in the hottest and least hospitable parts of the summer garden. These are derived from a series of somewhat tender species native to the Southwest and Mexico, particularly Agastache aurantiaca, cana, mexicana and rupestris.

Golden Jubilee is a hyssop of a different stripe entirely, owing its origins to a species named A. foeniculum, marked by its large habit, coarse texture and flowers that are borne mostly on stem tips as long, densely flowered racemes. A hybrid of this named Blue Fortune is another strong performer.

The desert hyssops, by contrast, are daintier, with silver gray and finely textured foliage, along with showy tubular flowers displayed from the ground up.

So, the five Golden Jubilees went in a corner of a partial-shade garden and became unexpectedly lovely, while the quest for the originally desired agastache type continued for a dry hillside on the other side of the house.

A now-classic hybrid Tutti-frutti embodies the appeal of the desert hyssops. It is aromatic, continuously in bloom until frost without the need for feeding or deadheading, and the conspicuous collar from which each flower erupts, the calyx, is decorative in itself, giving some blooms a bicolor effect. The colors can be deep magentas, pinks, salmons, oranges and yellows. Tutti-frutti is a strong, deep pink.

At a garden center, I came across a novel variety named Grape Nectar. It was completely loaded with pink-purple blooms on silver foliage. Resistance, as they say, was futile, and I stuffed five into my truck.

Later I came across this variety in the Trial Garden at Longwood Gardens, where it was even more floriferous. Horticulturist Jessica Whitehead is growing more than a dozen varieties at the Kennett Square, Pa. garden. Five are part of the Nectar series and include the somewhat strange Grapefruit Nectar, a yellow-rose bicolor; the lovely sherbet orange Apricot Nectar; and the rich rose-red Raspberry Nectar, which seems destined to become a hummingbird magnet.

Whitehead also liked those in a series selected from A. mexicana named Acapulco Orange, which has a rose undertone. “Vibrant and prolific,” she said.

The deep-rose-hued Ava is an older cultivar but showy and, at 4 to 5 feet, markedly taller than most, which rise to 3 feet typically. “It's really lovely if not new and exciting,” she said.

The smaller varieties get to 2 to 3 feet and work well as container plants. Smaller ones also look good at the front of a border. One of the best dwarf varieties is Sonoran Sunset, which is full of pink-purple flowers but stays under 18 inches. It would make a good container plant for full sun.

Apart from their enduring display in difficult locations, the agastaches also lure hummingbirds. So what's the catch?

If I lived in the Southwest or California, my garden would have far more of them. They are not reliably perennial in the colder East, and some are more likely than others to melt away from one year to the next. You cannot stick them in unimproved clay and expect them to survive, nor should you give them a thick mulch of wood or bark. Perfect drainage is a must; you can grow them in a gravel-soil mix, and a mulch of grit or pea gravel will help their chances of getting through a wet winter. Even with such care, few would have survived the severity of last winter, I would wager.

Whitehead and her colleagues at Longwood grow them as annuals (the problem is that they are sold as perennials with perennial price tags to go with them). I have gotten them to last a few years, but in an arid garden. If you can coddle them, or just want to plant one for the season, give the agastaches a go.