Direct Seeding Cool-Weather Flowers
Late winter or early spring is the best time for gardeners to direct seed (or “direct sow”) the seeds of flowers that grow best in cool conditions. These hardy varieties can comfortably tolerate a frost, including a snowfall, and thrive in the cooler daytime temperatures of March, April, and May to produce armloads of blooms in the later spring.
About Direct Seeding
Direct seeding refers to the process of planting the seeds straight into the garden outdoors, as opposed to starting them in cell trays indoors. It’s really that simple! Certain varieties of flowers prefer being directly seeded because they don’t tolerate the shock of being transplanted well (looking at you, larkspur!).
While some cool-weather flowers are better started indoors where they can be nurtured under controlled growing conditions (sensitive Iceland Poppies are a good example of this), many are tolerant of their seeds being tucked right into the garden. As a grower, I love when flower seeds can be directly sown - it saves space in the greenhouse and saves us the steps of hardening of trays to transplant.
Cool-Weather Flowers We’re Growing This Year
Because we plan our fields around our weddings, these are the cool-weather varieties that we’re direct sowing now to ensure they’re blooming for our bridal clients in the late spring months:
Larkspur is an easy-to-grow and productive line flower that comes in shades ranging from white, pink, blue, and the softest grays and purples; the latter is what we’re primarily growing this year for a dusty, textural late spring wedding. They’re closely related to delphinium, a short-lived perennial that is one of my favorite flowers in the field; by comparison, larkspur is more textural, much easier-to-grow, and a touch less elegant than delphinium.
Persian Cress is an airy, abundant green filler that adds a pop of whimsy and delicacy to any arrangement. We succession plant it so that it can be enjoyed throughout all of late spring, and use it in nearly every arrangement when it’s harvestable! Be sure to provide some type of support (horizontal Hortonova trellis is what we use) to ensure it grows straight.
Shirley Poppies are a pollinator favorite. What they lack in vase life (they last only a couple of days, at most, so we use them exclusively for day-of event work) they more than make up for in personality! Their paper-y petals, fresh citrus hues, and delicate stems add a pop of whimsy to any bouquet.
Ammi (aka “False Queen Anne’s Lace”) is a delicate, textural, romantic flower that is actually a member of the carrot family. Its lacy blooms make for a gorgeous filler - I especially love the Green mist variety. We’ll sow a couple successions of this popular and hardy flower so that we can enjoy it for a couple months in the late spring and early summer months.
Pansies ~ Thanks to Brenna Estrada from Three Brothers Blooms, there has been more interest in this gorgeous flower than ever before! We’re sowing some really special and romantic ones this year - “Chianti Mix” and “Sweet Pea Mix” are my two personal favorites, and look nothing like you’ve ever seen at a garden center before.
(We’ll also be transplanting our sweet peas and Group 1 snapdragons from the greenhouse to the fields this week - those are both best started indoors, however.)
Timing
In Zone 7a, including Greater Philadelphia, March is typically the month for these flowers to get tucked into the soil outside. The best timing can vary, and it’s not an exact science, because it’s impossible to predict future weather with any level of certainty. As a rule of thumb, though, once daytime temperatures regularly start reaching 50+ degrees and nighttime temperatures aren’t forecasted to be below 25, I feel comfortable direct seeding these varieties. This year, that was in mid-March; the last two years, though (some of the warmest on record in Philadelphia), I felt comfortable directly seeding in early March or even late February.
One of the most commonly asked questions is “what’s the lowest temperature that X variety can tolerate?” but, unfortunately, that’s a tricky one to answer. The seeds, seedlings, and plants can all tolerate different temperatures depending on where they’re at in their lifecycle and the extent of their root development. Moisture levels also play an important role (they can tolerate lower temperatures if they’re well-watered), as can other climate and location factors. Even within a single species of flower, there can be a broad range of cold-weather hardiness; snapdragons are a great example of this! That all said, it’s safe to assume that most cool-weather flowers can handle temperatures down to 25 degrees or so - and some can handle quite a bit lower.
