Yes, it’s that time of year.
For those who haven’t tried it before, starting your own seeds indoors is time consuming (as opposed to buying starts at the nursery), but it offers great benefits, including money saved, virtually limitless choice of varieties and the joy of watching live things sprout while the landscape outside is still covered in snow.
Here are some tips that will help produce the most successful seed starts possible.
When to start: Smaller, generally cold-weather plants (lettuces, greens and brassicas) should be started about four weeks before you plan to put them outside. Larger warm-weather plants (such as tomatoes and peppers) generally need six to seven weeks.
Calculate the outdoor transplant date (therefore, your indoor starting date) based on the last frost date in your U.S. Department of Agriculture plant hardiness zone (https://planthardiness.ars.usda.gov). For times from starting seeds to transfer, refer to http://go.uvm.edu/growingvegetables.
You can put the plants outside four to six weeks earlier with the use of simple low tunnels. For instructions on how to build a low tunnel, check out http://go.uvm.edu/lowtunnels.
Growing medium: Seed-starting mixes are generally made up of sphagnum peat moss and vermiculite. If you start with one of those, you will need to fertilize soon after the seeds emerge or pot up your plants in a growing mix containing more nutrients.
Nurseries sell special seed-starting mixes that contain mycorrhizae, a fungus that helps young plant roots access water and nutrients to become established more quickly. A 50/50 mix of compost and peat moss also will work fine and save you some money.
Don’t use regular garden soil. It will work, but the more compacted, less nutritious soil will likely lower the seedling growth rate, plus you’re importing whatever pathogens are in the soil, as opposed to starting with a clean mix.
Lighting: Avoid starting seeds in windows, as they will grow tall and spindly. As bright as it might appear to us, even a south-facing window is a pale imitation of the ambient totality of outdoor sunlight. The only time I’ve seen this work other than in a greenhouse, is in a southeast corner that had large unobstructed windows facing in both directions.
For artificial lighting, use cool-white fluorescent bulbs. Avoid incandescents, which skew too much to the red side of the spectrum and produce heat that can harm or kill young plants.
Advances over the past 20 years have led to bulbs little thicker than pencils, but whatever thickness you use, get bulbs that produce the maximum amount of lumens. Bulbs designed specifically for plant growth are commercially available and cost more.
Typically, 14-18 hours of light a day is considered optimal (timers help). Some seeds germinate best in the dark, while germination for other seeds is stimulated by the light. Seed catalogs and packets often will indicate the seed’s germination preference.
When planting light-stimulated plants, don’t bury the seeds. Just cover them lightly with peat moss, so they are able to get the light required to germinate.
Keep the lights as close to the tops of the plants as possible, preferably 1-2 inches. The light diffuses quickly as they get further away.
Watering: When first planting, it helps to pre-moisten your medium before placing your seeds, especially if you use peat moss, which initially repels water. I use a spray bottle, so as not to disturb the seeds too much. After that, water from the bottom, adding water to the tray holding the seed cells.
Your medium should be moist, never dry, but not so wet as to encourage mold or stem rot, also known as damping off. Add 1/4 inch of water in the tray when it is empty.
While covering trays with a plastic dome or plastic wrap can help keep soil moisture even, this may lead to surface mold from trapped moisture if left in place too long. So be sure to check seed cells often, and remove the plastic as soon as the seedlings emerge so they get enough light.
Follow these simple steps, and you should get healthy, vigorous starts for your garden.
Gordon Clark is a UVM Extension Master Gardener from Burlington.