Seed Starting 101

I can’t think of many things more special than starting a flower garden from seeds. Each late winter and early spring, we start thousands of tiny seeds in cell trays and soil blocks, and anxiously await their growth in our greenhouse. If you’ve never grown cut flowers from seeds before, you’re in for a treat ~ not only is it a rewarding and beautiful process, but the varieties available to grow are infinitely more exciting than the lackluster selection you’ll find at garden centers.

Thankfully, starting seeds is also typically pretty easy and affordable. Like with many things in life, there are expensive gadgets and complicated set-ups - but you don’t need the vast majority of them. I promise! The following guide is intended to provide home gardeners with a simple, affordable, and effective way to start seeds each spring.

What You’ll Need

The basics are simple: you’ll need a tray for the seedlings to grow in (under $10 available at garden centers or online - or you can upcycle an old milk jug), seed starting mix, a misting bottle, and an LED grow light. And, of course, you’ll need seeds. Some of my favorite seed suppliers include Johnny’s, Baker’s Creek, Three Brothers Blooms, The Farmhouse Flower Farm, Redemption Seeds, and The Flower People.

(Article coming soon on soil blocking, a method of growing healthy seedlings without traditional cell trays)

The Location

Generally speaking, growing in a sunny area indoors - like near a south-facing window - is the best choice. The supplemental light from the LED grow light will then provide the extra boost your plant babies need. Certain varieties, though, like delphinium, sweet peas, and pansies, thrive in cooler conditions. If you happen to have a greenhouse for these cool-weather loving plants, that’s the best choice, but a garage or cool basement can be a good option, too - just be sure to have a grow light that provides ample lighting.

The Timing

Here in Greater Philadelphia (Zone 7a, where our last frost of the spring typically occurs in early May), the majority of summer and fall flower seeds will get started in the month of March. Popular tender annual favorites like cosmos, celosia, zinnias, most herbs, strawflower, most ornamental grasses, will all get started in March, about 4-6 weeks before transplanting them to the field.

Some varieties, though, get started earlier - especially slow-growers like lisianthus or cool-weather flowers that thrive during the springtime, like sweet peas, stock, and group 1-2 snapdragons. Many biennials or short-lived perennials get started earlier (typically in late January or February), like foxglove and delphinium.

As always, be sure to read package directions to determine the best timing for your climate.

The Process

First, fill your cell tray with a quality seed starting mix. Seed starting mix is a blend of lightweight substrates especially designed to promote healthy growth in seedlings while maintaining proper moisture levels - it’s technically not soil at all! We prefer to make our own, or use Organic Mechanics’ peat-free version.

While most seeds need to be covered with a thin layer of the mix, other varieties - like foxglove and pansies - actually need light to germinate, so be sure to read package directions to determine how deep to plant the seeds. We typically add two or even three seeds per cell, just to ensure a higher likelihood of each cell germinating. For the tiniest seeds, like snapdragons, it might be helpful to use a toothpick to place them properly.

We then water them generously using a misting bottle (this is recommended over a traditional watering can, as that can result in a heavy pour, displacing the tiny seeds). Almost every flower seedling needs to stay moist during the germination process, so they may need to be watered multiple times per day. A humidity dome (a clear covering, usually plastic) can be used to keep moisture levels higher, but they’re typically not necessary - and should be removed once most of the cells have germinated.

We typically keep our LED grow light on for about 12 hours per day and keep them in the sunniest space possible. Most seeds germinate within 4-14 days.

An Important Note

Not all flower seeds transplant well. As a result, it’s best to “direct sow” certain varieties, meaning plant the seeds directly in the garden and, if this is the case, the seed packet will make mention of it. This is typically because they’re highly sensitive to root disturbance. Sunflowers, for example, are never recommended to start in cell trays.