Seeding Annuals for Early Bloom

By Sonoma County Master Gardener Rosemary McCreary

Spring-cleaning comes early and takes on a special meaning for gardeners seeking early summer bloomers. In February, we’ll be cleaning up stored containers and planting seeds of flowering annuals.

Naysayers may opt for buying flats of color spots instead, but for a truly personalized garden, there’s no substitute for planting our own. Besides, it’s much easier to find new or unique varieties and colors in seed catalogs than in any nursery or garden center.

If you’re thinking that February is too early to be concerned with summer flowers, visualize your garden in early May—as blossom-bare and then again in full bloom. By seeding now, you’ll have thriving plants ready to set in place after our last frost date, April 15, or for those in particularly cold spots, May 1. Gardeners in very warm micro-climates may have discovered an even earlier last-frost date.

In early February, start hardy annuals such as calendula, bachelors buttons, wallflower, and clarkia. Because these tolerate some frost, you can transplant them as early as March. Some gardeners prefer to sow them directly in garden beds—in fall or in early spring—which usually calls for extra time weeding as seedlings emerge. 

Half-hardy annuals such as cosmos, dianthus, nicotiana, and zinnias tolerate chilly days and nights but not frost and should not be direct seeded or transplanted until late April. Remember that all tender annuals are just that—tender; they thrive in summer warmth and won’t survive outdoors in cold weather.

Flowering annuals need warmth long before they’re transplanted, however. When started indoors—in a greenhouse, garage, or spare room—germinating seeds, seedlings, and young plants all benefit from spending their early days on a heat mat.

Along with heat, they’ll need adequate light after germination to produce strong stems. A sun-filled window is an option, but you’ll find far greater success if you use a dedicated full spectrum gro-light or an all-purpose florescent tube placed just a few inches above growing tips and adjusted upwards as plants grow.

If you do place plants in a window, turn containers frequently to maintain upright growth and remove them to a warm spot at night. All seedlings should be given 8 to 10 hours of darkness each night.

When preparing your own seed mix, forego using garden soil or recycled potting mix. These may contain fungal spores of damping-off disease, an infection that kills seedlings. For best results, begin with a purchased germination mix free of pathogens. Moisten it lightly prior to seeding. If you’ve used flats, 6-packs, and other containers previously, clean them first in a mild bleach solution for further protection.

Information printed on seed packets is always helpful, even for experienced gardeners, so be sure to check for required conditions such as need for light or a thin covering of soil. Remember that seeds buried too deeply will never push their tiny cotyledons above the surface.

Keep the soil evenly moist, never soggy. Use a lightweight clear plastic cover to create a greenhouse effect but allow for plenty of air circulation. After the first set of true leaves develops, apply a dilute dose of balanced liquid fertilizer every week.

A week before setting plants into the garden, acclimate them gradually to outdoor air, increasing exposure each day to harden them off, that is, to increase rigidity in leaves and stems in preparation for wind and weather.