Greenhouse grower John Whalen discussed practical guidance at the Delaware Horticulture Industry Expo on planning, scheduling, cultural practices and strategies to maintain healthy, pest-free annual plants. (Photo by Carol KInsley)
John Whalen, a fourth-generation nurseryman and greenhouse grower in Toughkenamon, Pa., has a lot of experience and opinions on growing annuals and he’s not reluctant to share them.
Speaking at a horticulture conference in Delaware this winter, Whalen outlined some of his production protocols for growing annuals in a greenhouse.
Whalen noted there are more than 18 macro and micronutrients a plant needs in order to grow, but each one is managed differently.
In vinca, his No. 1 selling bedding plant:
Nitrogen is for leaf growth and vigor. Deficiency is seen first in yellow lower leaves, progressing upwards to cover the whole plant. Too much N will result in fewer flowers.
Phosphorous is for roots and flowers.
When deficient, leaves will be a darker green cupping upward, leading to purpling of lower leaves then chlorosis.
A lack of potassium (for stress tolerance and overall health) causes chlorotic lower leaves, leading to brown lesions at the leaf tip and edges.
Deficient magnesium (for chlorophyll production) causes lower leaves to point downward and become chlorotic, leading to brown necrosis.
Not enough calcium (a key component in cell wall strength and development), and the immature upper leaves and newer leaves will develop little black spots and pucker, resembling insect damage.
Lack of iron causes leaves on top to yellow and works downward.
He said a high pH reduces iron uptake.
Whalen said he doesn’t put much stock in so-called “bloom busters” with high phosphorus content, High P can strip beneficial organisms from the soil, he said.
Discussing the mobility of nutrients in soil, John said he uses Osmocote, a controlled-release fertilizer that feeds plants for up to six months, when cultivating beds.
Timing of slow-release products is based on 70 degree days, he said, but when the weather is warmer, the nutrients wash out within 30 days.
He recommends water soluble products which are quick and cheap.
“Twenty-five pounds will make 2,500 gallons of fertilizer,” he said. With Osmocote, you can cover 10,000 square feet for $100.
He noted that annuals are “juiced up” when bedding plants are transplanted. Fertilizer quickly washes out of peat media.
Do not apply dry fertilizer directly to plants, he warned. “You can top-dress Osmocote, but if it’s extra dry, add water.”
He added he likes Osmocote for containers, too.
Annuals grow fast and can produce tons of flowers in a short time, he said.
His recommendation was to mix water-soluble fertilizer with water according to package directions and apply every seven to 14 days during growing season — to both in-ground and container plants.
Whalen said one application of controlled-release fertilizer before planting, in both containers and garden beds, will feed plants gradually over three to six months, or most of the growing season.
Asked about dipping a plug into a fertilizer solution, John quickly answered, “No, that could spread disease.”
A final warning might have surprised Master Gardeners in the audience: “Never scratch or break up roots of annuals. That does more damage than good,” Whalen said. “It allows disease to enter. Being root-bound is not a thing to worry about.”
Whalen is the fourth generation to control what was a landscape company founded by his grandfather in 1933 — at age 15. Whalen Greenhouses produces nearly 2 million plants annually in 140,000 square feet of greenhouse space, with 3 acres of outside production.
“Everything we have is started and grown here, except for tropicals,” Whalen said.
The wholesale company specializes in contract growing for greenhouses, landscapers and garden centers.
They grow seasonal crops such as forced bulbs, bedding plants, hanging baskets and mixed containers for spring, then mums, pansies, kale, dianthus, poinsettias and wreaths for the later season.
