Consider adding these perennials to your lineup

Many specialty cut flowers don’t make it onto large-scale wholesalers’ lists because of their short bloom period. A fairly typical perennial may bloom for just three weeks, leaving a very narrow sales window for clients who can’t memorize the hundreds of species available throughout the year. A new flower, no matter how long lived or usable, that hasn’t shown up on the list for a year doesn’t ring the client memory bell, so the first week on any wholesale truck is usually a matter of re-acquaintance. The second week of availability brings familiarity during which a buyer gets a feel for the product, and only on the third week, just as the harvest is nearly finished, do clients really get excited—and then it’s gone for a year. Hence, wholesalers shy away from many specialty cuts.

But there are ways for growers to lengthen the market window of many species. Scheduling, early and/or late pruning, shade application, and cultivar selection, in addition to the usual techniques of greenhouse planting and cooler usage, allow growers to extend a natural sales period of just a few weeks to as long as the entire summer.

A little clever scheduling lengthens the sales season from three weeks to all summer for some perennials. We plant new crops of solid sellers like delphinium every spring, putting two hundred-size plugs in the ground a week or two before our last frost date (May 10). These same-year plants typically flower in July, shortly after prior years’ plots finish, lengthening a three-week harvest to six weeks. To lengthen the window further, we immediately prune—severely—after harvesting last year’s delphinium, which then blooms in August as the same-year crop finishes. The second crop stems are of shorter stature, of course.

Heliopsis responds to these techniques similarly, and both flowers can be manipulated further by pruning before bud to delay flowering. Pruning after harvest, of course, results in a second late crop, but because so many other yellow flowers come in season late—black-eyed Susans, sunflowers—we normally just write heliopsis off for the rest of the year. If you organize your pruning and sequence planting perfectly you can harvest these crops throughout the summer. Hopefully, your market can withstand the onslaught. If not, you may end up plowing under excess plantings.

Asclepias tuberosa performs well using the last year/this year scheduling, and reacts favorably to pruning at any time, allowing the grower to delay flowering or string it out throughout the summer. Its brethren, incarnata, is less flexible, so while we plant a new crop almost every year to add to the prior year’s, we rarely get much flowering from the same-year plants—those in longer season growing areas may get different results. We find it doesn’t really respond to pruning as well, either.

Perennial scabiosa, a prolific bloomer that produces continually if harvested hard and deadheaded to prohibit seeding, still has its limits, and starts looking pretty shabby after many weeks of cutting. Harvesters may not cut deep enough, resulting in short, unusable stems later in the year, and markets may not match production, creating a rise in deadheading time that becomes unprofitable. If you plant a new crop of plugs prior to the last frost, the old bed can be mowed down about the time they begin blooming, making for a seamless sales period. The new crop stems will tower above what the old plants have been offering, throwing bigger blooms and sturdier stems that far surpass typical wholesale offerings.

Fooling Mother Nature

We treat Matricaria and black-eyed Susans, technically multi-year species, as biennials, sometimes as annuals, and sometimes as tri-annuals, since they can occasionally make it into a third year. Because they don’t require winter dormancy, these crops bloom the same year as planted, but to get an earlier bloom we nurse last year’s crop through the winter (this doesn’t always work for Susans if the winter is too harsh) for a harvest that begins 3-4 weeks before same year crops.

These two crops are the cockroaches and coyotes of the cut flower trade, withstanding grower and nature misuse with ease, absorbing a severe hacking at almost any stage and coming back with a vigorous rebloom. You can, however, be a little too ambitious with pruning—don’t eliminate the black-eyed Susan rosettes or you might kill the plant; instead lift your weed whacker or mower just above those lower leaves so something remains on the plant to retrieve the sun’s energy for further growth.

Matricaria acts as a year-round filler for our clients, so with proper timing we offer it on a continual basis. Greenhouse plug plantings beat outside beds to bloom by only a few days, so we rarely use inside crops, saving that valuable space for other crops. It must be said, though, that an inside Matricaria crop exceeds in quality any outdoor planting, with taller, fuller blooms and thicker stems, but fewer of them, since without cold weather the plant doesn’t “stool out” with multiple stems as outside crops, which face constant supplies of cold nights, do.

In any given year, we might plant Matricaria plugs in a greenhouse, then in a hoophouse, then early outside (It tolerates very low temperatures—our plugs have taken 20-degree nights with minimal damage.) with later plug plantings in May and June. Between shearing back part of last year’s crop, sequence planting, and mowing after harvest for a second bloom, we have continual supplies of Matricaria—if our planning is right and the weather cooperates.

When sequence planting either fast-growing perennials or annuals, any grower needs to note that the “days” to bloom listed on seed packets or spec sheets don’t really refer to real time but to an average summer day—though what area of the world that average is taken from I’m not sure. Unless you live near the equator, where days and nights tend to be of similar length all year and temperatures stay stable, that average summer day might equal three April days when comparing light and heat units. Thus, three weeks between plantings in April and May equals about one week in the summer for us, and the same might be said for fall plantings, though we have such severe winters that we have little to no experience with late seedings or plantings (our first frost often falls between September 10-20, so adjust your efforts accordingly).

Some perennials, while not known for repeat performance, still respond to manipulation by pruning—you just have to cut back before any bolting occurs. A nasty May hailstorm taught us this when it knocked the perennials down, destroying a delphinium crop just a few days from bloom and shredding any foliage already emerged on other perennials. We mowed portions of a number of crops back to the ground, hoping to salvage the year’s blooms, and discovered that globe thistle, mowed before bolting occurs, starts flowering right as the unmowed crop finishes—a great discovery, since designers love this crop and we could sell it all year long if we just knew how to extend the bloom time. Heuchera, in bud at the time it hailed, got mowed down and came back with a vengeance, meaning we will be able to have a normally timed crop next year and, in addition, a secondary crop to follow it.

Bush clematis, vigorous as they are, respond to pruning both before bloom and after without suffering long-term damage. recta and integrifolia can be manipulated at the grower’s will to lengthen out the market season, and since both re-bloom—and bloom again in longer growing season areas—can be available throughout the summer. Taller, vining clematis that tolerate or need spring pruning can be cut back in stages early in the year, to stagger bloom time somewhat—though the effect has its limits. ‘Paul Farges’, an extremely vigorous early bloomer with small white blossoms, yields blooms for a long period if you cut some plants back early, others a week or two later, and others after that. Once established, this clematis can almost be said to be immortal, so hard pruning seems to matter not at all.

Rules of Thumb

In general, later stems of species pruned before normal flowering tend to be considerably shorter than those left uncut, so in high light areas avoid using the technique on short species. And refrain from pruning slow-growing perennials—every leaf counts when it comes to energy and nutrient collection, so removing foliage amounts to depriving an unemployed plant of its bank account.

Try using shade to extend a given species’ bloom. While daylength sensitivity and heat unit requirements may limit the elasticity of a particular species’ flowering period, most species have at least some wiggle room in which to bloom and shade can help you take advantage of it. For us, a field-grown crop of phlox finishes blooming just as a counterpart crop under shade begins, and the crop under shade is taller and lusher, being protected from our harsh, dry climate. Phlox is particularly amenable to all sorts of manipulations: you can sequentially plant the roots to get blooms throughout the year, but you’ll have to work out the timing for your climate and latitude.

Other species not hindered by a tight daylength window likely can be treated similarly with shade: monkshood, lobelia, lavender, and lysimachia among them. Also, cultivars of a species labeled “garden” often bloom shorter than their parents do, too short for the cut flower trade, but under shade they may reach a stature that makes them usable—give that species you thought you couldn’t use a try in your shadehouse.

Different cultivars of a given species often bloom at generally similar times—some species in spring, some in summer, others in the fall—but particular varieties may bloom a few days earlier or later than their counterparts. Early veronicas (often shorter ones) can bloom three weeks before later, taller varieties that require more time to develop. While the stem length and bloom size vary and the hues differ slightly, the shape and general color designers want remain. It’s not a perfect solution, but not every floral situation is an emergency demanding exactness.

You can also use greenhouses and hoophouses to alter bloom time for many species, including phlox, bringing them to bloom earlier or later, as needed. This works better, of course, for crops that don’t require vernalization (a winter cold period) to bloom, though if you’re willing to use your greenhouse space you can fall plant those species, too, to extend the market window.

A cooler, of course, also extends the market window, normally by at least a week. Once you’ve kept a product in water for a week, though, you best start considering most flowers as an event-only sale, since vase length diminishes after being held for long periods.

Do a test run before you go all out with any season-extending technique, as some one-and-done species will indeed be done if you prune them—the most obvious ones being bulb crops like lilies, tulips, eremerus, and daffodils—and some species can’t be pushed either forward or backward in the season since they have very specific daylength needs. If you grow a crop that your clients constantly clamor for, give it a longer availability period to heighten your operation’s profitability.

Ralph Thurston, along with Jeriann Sabin, is owner of Bindweed Farm in Blackfoot, Idaho, as well as co-author of Deadhead: The Bindweed Way to Grow Flowers and All Pollen, No Petal: Behind the Flower Farming Dream.  

Contact him at [email protected]