If you’ve never jumped the gun on spring planting and lost precious seedlings, you haven’t been gardening long enough. We in the colder gardening zones (from USDA Zones 3-6) are chomping at the bit come spring to see some growing activity and color courtesy of growing plants.
When the soil is wet, working with it is bad in so many ways. Walking on or working in wet soil makes it harder for plants to grow in it. If you’ve ever had the wind knocked out of you, then you know what happens each time the soil is trampled. It’s up to the plant’s roots to work their way through the soil in search of moisture and nutrients. They won’t get far in a soil with no airspace.
Here’s how to get a sense of moisture in your soil: Scoop up a handful from the surface and squeeze—just as hard as a firm handshake. Release your grip and see what you have. If it looks like the beginning of a mud patty, it’s not ready yet. But if it crumbles apart as it sits in your hand, scoop a few inches below the surface with a trowel and do the squeeze test. That’s the important level, where plants’ roots will be growing. Soil dries from the surface downward, so if the weather remains sunny and dry, it won’t take long before it is ready to work in.
Garden centers open their doors to spring around late-March/early-April. But if you live in Zone 6 or colder, you won’t want to plant heat-lovers like tomatoes and zinnias outdoors until around the second week of May or even later. Buy a soil thermometer and follow the temperature requirements for tomato plants when determining when to plant most summer annuals, and you won’t go wrong. According to the University of Missouri Extension, the soil temperature should be above 60 degrees F for tomatoes (and other heat-loving annual plants) to thrive.
You can still plant some containers if you use the right plants and methods. One crucial consideration is soil drainage. Days are still on the short side, temperatures on the cool side, and there is little doubt it’s still the soggy side of spring. I start with the lightest soil I can find, and add some extras, mixing it up in a big Tubtrug®. Materials like lava rock chips, large poultry grit, orchid bark or pine bark fines, and perlite have irregular surfaces, which improves pore space and allows water to drain quickly away from plants’ roots.
Stick with large pots—at least 12 to 14 inches in diameter. The larger the pot, the less water it will require when the temperatures reach into the 80s and higher. Don’t forget the fertilizer, because the potting mix you use either has none of the nutrients your plants will need, or just enough to get them going. I use Osmocote when I first put the container together, but I also use water soluble fertilizer as well. Osmocote is activated by heat; it’s important to have it in the mix for the warm days, but it doesn’t hurt to use the liquid or powder materials that are mixed with water when the containers are planted and ready to be watered in.
Now comes the fun part. Head on over to your favorite garden center for inspiration, but be sure to drive a large enough vehicle for stowaways. Two of my favorite sources are Sunrise Greenhouse in Grant Park, IL and Vite Greenhouses in Niles, MI.
Plant development and distribution leader Ball Horticultural Company is responsible for a large number of plants in most garden centers throughout the country. Ball’s Brand Manager, Claire Watson recommends Cool Wave Pansies for early-season color. “Cool Wave and other cool-season plants that gardeners find in stores are usually acclimated for the weather,” said Watson. “Any standard-size six-inch container of Cool Wave Pansy at the store should be fine to stay outdoors. They even take a frost!”
Very young plants are a different story. Watson says that seedlings and very small plants should be kept indoors until the plant has six to seven true leaves. At that point, she said, they can be gradually acclimated to living outdoors full time. When temperatures start to climb above 50 degrees during the day, the plants can be taken outside for a few hours during daylight. Bring them in at night, and repeat the process adding a few more daylight hours outdoors until the plants are ready to go in the garden or their final container.
Watson’s advice for a practice referred to as hardening off can be applied to any plant that’s spent its life so far in a greenhouse. Even greenhouse-grown perennials can benefit from a gradual move to the outdoors. Small containers from the nursery dry out very quickly outdoors in the sun and wind. I like to start plants out in a partly sunny location out of the wind to begin with, especially those that are pot bound.
In addition to pansies, alyssum, Osteospermum, Dianthus and snapdragons are great for mixed combos. These plants grow best in cooler weather, and generally bloom and look good from early spring through the onset of warm summer temperatures. Watson says that once it gets to be beach weather, it is best to remove the spring flowers and plant summer annuals like Wave Petunias. Until then, she offers some decorating tips using cold tolerant plants.
Gardeners can find other cool choices at garden centers. I always look for stock Matthiola incana, especially the white-flowered doubles, which I find to be the most fragrant. The most comprehensive garden centers have them as plants, or you can find seed at Swallowtail Garden.
It’s not a bad idea to invest in some protective plant covers for spring. The lightweight fabric won’t crush plants, and can add as much as 10 degrees of warmth.
Anytime Pansiola® Series (Viola x wittrockiana)
Cape daisy (Osteospermum spp.)
Cool Wave® Pansies
Cupflower (Nierembergia hippomanica)
Dianthus chinensis
Dusty miller (Centaurea cineraria)
Ornamental cabbage (Brassica oleracea)
Phlox drummondii
Sedum spp.
Snapdragon (Antirrhinum majus)
Spike (Cordyline spp.)
Stock (Matthiola incana)
Sweet alyssum (Lobularia)
Perennials straight from the greenhouse perform very well in containers. Some are labeled perennial in our zones, but will peter out when the heat comes on, while others are naturally short-lived in our climate. They include:
Bellis perennis
Ice plant (Delosperma dyeri)
Spanish lavender (Lavandula stoechas – tender perennial)
Pericallis (tender perennial whose ideal growing temperature is between 50 and 65 degrees F.)
Mullein (Verbascum – the hybrid ‘Southern Charm’ is the most readily available)
It’s not too early to at least think about what you’ll be planting in those empty containers. Don’t wait until you get to the garden center. When bombarded with so many colorful choices, the brain cells of cold climate gardeners turn to mush. Make a plan, write it down, and be ready to revise. Because I guarantee you will.