August 2008 Culture

Agastache ‘Raspberry Summer’ By Paul Pilon

Summer gardens are incomplete without the presence of agastache. Few perennials provide such a stunning display of long-lasting color.

'Raspberry Summer', a recent introduction from Terra Nova Nurseries, produces an abundance of raspberry-pink tubular flowers atop attractive clumps of bright green, fragrant foliage.

With its ease of production and first-year flowering, agastache 'Raspberry Summer' is a great addition to summer perennial programs. In midsummer, it produces an abundant supply of flower clusters that are highly attractive to bees, butterflies and hummingbirds. In fact, the name of the genus agastache translates to "many flower spikes" in Greek. The fragrant foliage is resistant to deer feeding, and once established, agastache is fairly drought tolerant.

In the landscape, agastache grows best under full sun in locations with moderately moist to dry soils. Do not plant in locations with overly wet soils during the winter months or plant mortality is likely. It reaches 26-32 inches when flowering and spreads to 24 inches at maturity. It is hardy in USDA Hardiness Zones 6 to 9 and AHS Heat Zones 10 to 3. 'Raspberry Summer' is ideal as a background plant in flower borders and is also commonly used as accent or specimen plants or in cutting gardens, mass plantings and container plantings.

Propagation

'Raspberry Summer' is a patented variety and currently is propagated only by means of tissue culture; self-propagation is prohibited at this time. Most growers will purchase cultivars from tissue culture as 72-cell or larger-sized plugs from licensed propagators.

Production

It is best to produce agastache in large, 1- to 2-gallon-sized containers. They prefer to be grown in a well-drained medium with the pH maintained between 5.6-6.4. Many commercially available peat- or bark-based growing mixes work well, provided there is adequate drainage. Although they can be somewhat drought tolerant in the landscape, agastache prefer to be kept moderately moist when they are grown in containers. When irrigation is necessary, water them thoroughly, then allow the soil to dry slightly between irrigations.

They are considered light to moderate feeders. Nutrients can be delivered using water-soluble or controlled-release fertilizers. Growers using water-soluble fertilizers can apply 75- to 100-ppm nitrogen with every irrigation or use 200 ppm as needed. Controlled-release fertilizers are commonly incorporated into the growing medium prior to planting at a rate equivalent to 1-11?4 pounds of elemental nitrogen per cubic yard of growing medium. Growing them under high-fertility regimes generally causes them to become very lush and may delay flowering.

'Raspberry Summer' produces a tall plant when it is grown in containers and marketed in bloom. To maintain plant quality, commercial growers will have to combine both cultural and chemical methods of controlling plant height. The first approach to reducing unnecessary plant stretch during crop production is to provide adequate spacing and to withhold water and nutrients (namely, avoid providing luxury amounts).

To produce more compact and sturdier plants, it may be necessary to apply plant growth regulators. Several of the commercially available plant growth regulators are effective at controlling plant height. Depending on geographic location and the amount of height control needed, the following PGRs will provide effective control: daminozide (B-Nine, Dazide) at 2,500-5,000 ppm, daminozide at 2,500-5,000 ppm + chlormequat chloride (Cycocel) at 1,000-1,500 ppm, paclobutrazol (Bonzi) at 30-60 ppm, or uniconazole (Concise, Sumagic) at 5-10 ppm. In most instances, it will require multiple foliar applications to obtain adequate height control.

Insects and Diseases

Agastache can generally be produced relatively free of insects and diseases. Occasionally, aphids, spider mites, thrips and whiteflies may appear, causing only a minimal amount of crop injury. The primary diseases growers should watch for are downy mildew, Heterosporium leaf spots and rust. Pythium and Phytophthora may also be observed, particularly if the root zone is kept consistently wet or if the growing media has poor drainage. These pests can be detected with routine crop monitoring; control strategies may not be necessary unless the scouting activities indicate actions should be taken.

None of these insects or diseases require preventive control strategies. Growers should have routine scouting programs to detect their presence early and to determine if and when control strategies are necessary.

Forcing Agastache 'Raspberry Summer'

can be forced into bloom throughout the year provided a few guidelines are followed. Vernalization is not required for flowering, and 'Raspberry Summer' will flower readily without receiving a cold treatment. Providing a cold treatment provides little to no benefit as far as flowering is concerned. They can be successfully overwintered provided they are obligate long-day plants, absolutely requiring long days for them to flower. To obtain flowering when the photoperiod is naturally short, I recommend providing at least 14-hour photoperiods or night-interruption lighting. The time to bloom after the proper photoperiod is provided is a function of temperature. Depending on the size and the age of the starting materials used, it will take 10 to 12 weeks to reach flowering when they are grown at 67¡ F.

Availability

Agastache 'Raspberry Summer' is brought to the industry by Terra Nova Nurseries (www.terra novanurseries.com) from Tigard, Ore. It is available to growers most commonly as finished plugs from Terra Nova or other reputable plug producers throughout the country.