Walters Gardens in Zeeland, MI, grows Proven Winners’ Heuchera ‘Black Pearl’ Growcoon plugs as part of its portfolio of products. Photos: Andrew P. Jager, Walters Gardens
The last few years have shown an uptick in consumer interest in perennials. They are already widely available, but growers are considering adding more varieties to their catalog or adding perennials programs if they are only growing annuals.
As you’re planning your crop schedule for next season, here are a few insights from perennials growers. Head Grower Drew Koschmann of Walters Gardens and Lead Grower Chris Adler of Willoway Nurseries, both on Greenhouse Grower’s Top 100 Growers list, offer tips and tricks for your perennial program.
Young Perennials
At Walters Gardens in Zeeland, MI, the starting material is either tissue culture or cuttings. Certain crops are produced from seed or divisions, as well. In some cases, the genus dictates which propagation method is used. For example, Koschmann says hosta cannot be produced from cuttings. When tissue culture comes in, a quality control team reviews the material to make sure the pieces are good for planting.
Growers are looking to ensure that there is a root and callus on each piece of plant material. If there are no roots, growers may use a rooting hormone and then plant. If that doesn’t work, pieces without roots are thrown away. Growers also look for mold in the bags, and dump plants with mold. Walters Gardens receives cuttings from South America, and sometimes it is challenging if there are flowers soon after planting.
“If we stick cuttings and seven to 10 days later there is a flower, that’s not a good way to build size on a plug,” Koschmann says. “We’re talking with suppliers about how to minimize flowers in cuttings.”
In some cases, like with hibiscus, Walters Gardens uses tissue culture and cuttings. Starting with tissue culture helps start the crop clean, and taking cuttings off the tissue culture keeps the numbers high, Koschmann says. Cost is also a factor when choosing tissue culture or cuttings. In most cases, tissue culture is at least twice the cost of cuttings, he says.
When producing plugs, Walters Gardens works with Elle Plugs and Growcoon. The growing team has found that blends with no sticks work well for the Elle machines. Berger’s BM2 blend of peat and perlite does a good job of providing that consistency.
For some genera, a bark-based mix is the way to go, which includes composted pine bark, peat, and perlite. For larger plugs like 20-count and 30-count, Walters Gardens is trialing using percentages of HydraFiber.
After conducting tests on the water quality at the operation, Koschmann and his team decided to use a 16-3-16 CalMag blend from Plant Marvel Laboratories for fertigation. Koschmann says the operation uses city water, which is low on calcium, so more calcium is added to the irrigation water through the fertilizer blend being used. Growers also adjust the nitrogen parts per million (ppm) throughout the year. This blend allows for even growth and minimal top stretch.
While propagating, Koschmann says growers use a low concentration of 12-2-12 at 50-75 ppm with a constant mist as the callus forms and roots develop. Some genera need extra iron to help with leaf coloring, such as blue leaf hostas and brunnera.
Finished Plants
Willoway Nurseries in Avon, OH, grows 700 varieties of perennials, adding up to 1 million perennial plants grown each year, according to Inventory Manager Kelly Kall.
Lead Grower Chris Adler says pest and disease control is a critical component of production. They scout for pests and diseases and use biocontrols, but it’s most important to know exactly what you’re looking for. Certain plants are more susceptible to particular pests and diseases than others. For example, some perennials are more likely to develop powdery mildew, while others are more prone to having thrips or aphids.
“It’s important to know the plant and what it’s susceptible to, whether it’s a bacterial blight, fungal issue, or insect,” Adler says.
Willoway Nurseries uses plant growth regulators (PGRs) on perennials, but not as much as they would for annuals. Growers use PGRs to get the plant to bulk up. Some perennials are bolting long during production, and a PGR could be used to get them to hold longer so they will fit on a rack prior to shipping.
“A lot of people make a mistake in thinking that a PGR stops growth. A PGR does not stop growth, it controls the growth,” Adler says. “You can’t wait for the plant to get to a certain height, then spray to stop it. You have to spray early on to slow the growth and build the plant. It’s better to do two to three lower applications rather than wait until it’s too big and try to stop it.”
Adler says one of the biggest mistakes he sees is related to trimming. Plants may have a growth spurt, then growers trim them. But if a grower does not know exactly when and how to trim, or if the plant should be trimmed at all, the plant could become unsalable. Each plant has its own trimming process, and growers should be trained across various genera that they work with.
As for environmental conditions, Adler advises that Willoway keeps the perennials relatively cool, from 40 to 68 degrees. Some perennials, like hellebores, like it even colder. The growers do not manipulate light much. In the north, he says growers tend to try to hold plants and keep them vegetative, because perennials like to move early.
“We try to hold off flowering so they’re in color in May, and they look their best at the garden centers,” Adler says. “We’re usually at a long day anyway. If anything, we use lighting to keep plants vegetative rather than to initiate flowers.”