Jen carrying trays in an HMOS greenhouse

Whether you live in Washington or Maine, Arizona or Tennessee, your time has come—time to dust off your grow lights, unfurl a seedling heat mat, and soak your cell trays in soapy water. Because even if there’s still snow on the ground, frost deep down and a chill in the air, somewhere nature is making its first stirrings and the season of hibernation will soon be loosening its grip. So, in a few sections, we’ll walk through the seed starting season together. We’ll start with gathering your materials and the information you need to make a transplant plan, and then sow the first seeds of the season: alliums.

Last Frost Date and Planting Dates

The very first piece of information you need to know when getting started is the “last frost date” in your area. This is the latest date a frost is likely in your area, and you can find out yours here. Knowing this date will help you determine when to start transplants so they’re just the right size when they get planted out.

Next, take your last frost date and plug it in to Margaret Roach’s Planting Calculator. For example, by plugging in my last frost date (Memorial Day) I can see that the first crop I need to start is onions on February 23rd. However for the purpose of this article (and for the benefit of those lucky enough to live in slightly warmer climates), we’ll use May 1st as our happy medium. This moves the first onion planting date to January 23rd—so I guess we’d better get started!

Location, Location, Location

You’ll find that if you set up your grow light in a place that you walk by several times every day (such as in the kitchen or living room), you’ll be more likely to take good care of your baby plants. So, even though the basement is probably the most popular place to start seeds (and other messy projects), it’s a good idea to consider if they’ll receive enough attention there. A well-traveled location is especially beneficial for newer gardeners, because you notice right away if something goes wrong. You'll also know if your plants are comfortable—baby plants and people like similar conditions—and they will be happy in an area that is between 55-70ºF with moderate humidity. Right next to the front door or directly over a heat register would be “uncomfortable” places for you—and your starts. Whatever spot you’re considering, just ask yourself if you’re comfortable, and they will be too.

Light


Margaret Roach's adjustable light stand

Unless you have access to a heated greenhouse, you will usually need grow lights to produce your own transplants. The light coming in through a sunny window is not enough and will result in plants that are weak and “leggy” (elongated from stretching to reach the light). While you can splurge for a plush setup, grow lights don’t have to be fancy or expensive to work well and last for years. And the best news is, they now use less energy than ever before. The most affordable option is to use standard shop light fixtures available at home improvement and hardware stores. You then have the option of T12, T8, or the newest T5 bulbs. (T refers to “tube”, and the number refers to the diameter of the bulb.)

With the old T12 bulbs, you really needed to use one incandescent bulb and one fluorescent in each fixture—neither bulb produced enough of the light spectrum to produce healthy transplants on its own, and you still needed to keep the bulbs within one inch of the tops of the plants. The newer T8 bulbs are 40% more energy-efficient than T12s and plants can be up to 2” from the bulbs. Two four-foot T8 bulbs and a fixture cost around $30 in retail stores. The T5 is the newest option, also known as a “high output” fluorescent, is 9% more efficient than a T8, and is so intensely bright that plants must be at least 3 inches away from the bulbs to avoid scorching. The bulbs are also thinner and therefore more breakable.

You will need to figure out a way to raise and lower the fixture as the plants grow (most people hang them on adjustable chains), and a timer is a very worthwhile investment to make sure your seedlings receive the ideal 14-16 hours of light per day. Lots of people opt to purchase a complete seed starting set-up—like these from Gardener’s Supply—to avoid these hassles. You can also make your own, like this clever one from Margaret Roach.

Temperature

A seedling heat mat is useful (some might even say essential) for starting heat-loving crops like tomatoes, peppers, eggplant, basil and more. If you’re starting these seeds in an area that is consistently right around 70ºF, you may not need one. But generally you’ll get the most consistent germination using a heat mat, and the investment is well worth it—they last a long time and will avoid time and money lost on poorly germinated seeds. Even cold-tolerant onions and leeks germinate best at 75-85ºF. As soon as your seeds germinate, they should be removed from the heat mat and placed under lights. Note: Never attempt to start seedlings in the oven. The oven cannot provide consistent heat in the range suitable for seedlings and also generates fumes that are toxic to them (the fumes are vented from the oven during baking, but cannot escape at low temperatures).

Soil


HMOS Seed Starting Kit

Good quality soil is always important, and not all potting soil is created equal. At High Mowing we offer only one type of potting soil, from Vermont Compost Company because we think it is, quite simply, the best. We offer this soil as part of our seed starting kit, which includes a 50-cell plug tray, an open flat without drainage holes, a clear propagation dome to hold in moisture, and a 6 qt bag of potting soil from VCC.

Ask around for potting soil recommendations in your area—both Extension and Master Gardeners are great resources. Make sure that the soil is suitable for organic production and is used by commercial customers that depend on it—otherwise you may find that the quality is poor, nutrients are missing, or worse still that it contains chemicals like herbicides that can harm your plants. It is not necessary to choose a “germination mix” specifically. This just means that the mix is finer and larger chunks have been screened out—which you can easily do with a piece of hardware cloth or by hand.

Containers


Trays in the HMOS greenhouse

The variety of containers that could be used for starting seeds is literally infinite. Everything from cow pots to egg cartons to yogurt containers can be used, but for simplicity’s sake I recommend an ordinary cell tray (new or used). A 50-cell tray will provide plenty of room for each plant to get started, without giving so much room that smaller seeds “drown” in a large volume of soggy soil. When the roots fill the cells, the seedlings can be easily scooped out with a butter knife and planted in 4” pots. Biodegradable pots have advantages, but may fall apart before planting, and can’t be reused each year (ultimately costing more). And while you often see biodegradable pots advertised as being plantable directly in the ground, this sometimes causes problems—especially with coir (coconut fiber) pots, which degrade slowly and wick moisture away from the plant. As an alternative, you can also build simple wooden flats or try this individual paper pot maker to make pots from newspaper. If you’re going to reuse pots, flats or trays, wash them in warm soapy water and rinse thoroughly before planting to avoid introducing any diseases from last year.

Let’s Get Sowing!


Taylor filling flats in the greenhouse

Now that you’ve gotten your materials together, it’s time to sow the season’s first seeds! And they are: onions and leeks (alliums). Alliums require a very long season to mature, which is why we start them so early, 8-12 weeks before planting out. Ready? Here we go:

1)      Moisten your potting soil. Add a little bit of water and mix with your hand, and keep adding a little more water until it feels just barely moist (but not wet or soggy).

2)      Fill your tray or pots with the moist soil to within 1/2" of the rim, tamping down lightly as you go.

3)      Sow your onion or leek seeds on the surface of the soil, being careful not to crowd them – there should ideally be 2-4 seeds per cell or square inch, and certainly no more than 10 if you’re really trying to stretch your space. The more densely you plant them, the thinner and more vulnerable they will be at planting time. My goal is for them to be almost as big around as a pencil by planting day.

4)      Cover the seeds by lightly sprinkling about 1/8-1/4” of potting soil over them, then gently water in. If you have one, cover your tray with a propagation dome to hold in moisture and place the tray on top of a seedling heat mat.


Stephen seeding trays in the HMOS greenhouse

5)      Once the seeds have germinated, move the tray from the heat mat and place under lights. Water gently when the surface of the soil becomes dry to the touch.

6)      As the plants grow, gradually raise the lights so they are 1-3” from the top of the plants. When the plants reach 5” tall, use scissors to trim them back to 2” as this will encourage them to grow thicker and stronger (and the onion trimmings are delicious in sandwiches & soups!) At this point, you can begin hardening off your onion starts for transplanting.

Stay tuned! Next week we’ll cover starting your next batch of crops, plus some pointers on that all-important period of “hardening off”.

Check out our previous posts, Budget Seed Starting on a Small Farm and When to Plant (& Succession Plant): Using Margaret Roach’s Planting Calculator