March is a great time for seed starting for many annual vegetables for most of the US! With seeds you have greater choice of the variety as well as the preparation and care of the plants used to generate your seeds at less cost than purchasing seedlings at a local nursery or farm.

There are a few key things to consider when starting seeds. The first is timing! How long do plants take to germinate and grow into a seedling that can be transplanted? When can your plants go in the ground in relation to the last frost date in your area and how long will they take to mature? Working in a spreadsheet or notebook can help you keep track of timing of when to start seeds, when to begin hardening them off, transplant and harvest times, as well as notes about how that worked each year helping you learn as you grow! There are many great calculators online to help you determine best starting dates for the plants you want to grow. Some of my favorites include The Old Farmer’s Almanac (includes planting timing based on moon cycles as well as frost!) and  Johnny’s Seeds

Once you have selected what to grow and when to start seeds you need to decide how many of each plant you want to grow based on the amount of harvest needed and space available. Most seed packets come with information on how much plants produce, seed starting timing, spacing in the garden and other valuable information. Sometimes its nice to look at tables with this information to cross reference multiple plants without needing all the seed packets on hand! Planting guides online are helpful for this task. Living in New England, I like Maine’s Fedco Vegetable Planting Guide and Oregon’s Territorial Seed Company Planting Guide which have information on a wide variety of commonly planted vegetables. If you live down south you might consider checking out Southern Exposure Seed Exchange for planting guides and calculators more suited to warmer climates

Finally you need to choose a method of starting seeds. Traditional seed trays are made of plastics which are challenging to recycle. Try purchasing compostable materials that can be planted with the seedling (great for transplant sensitive seedlings), making your own pots with black and white newspaper, reusing plastic containers like yogurt cups or strawberry clamshells or skip the container all together and try soil blocks! Soil blocks are a great way to start seedlings, providing quality nutrients to the seedling while air pruning roots, helping to prevent transplant shock all while eliminating the need for plastic pots! You can purchase a soil blocker and special soil mix but you can also mold wet soil mix you make yourself with your hands!

Eliot Coleman, who has pioneered the use of soil blocking for organic market growing in the US has a simple recipe to make your own seed starting mix at home. To make 1/2 bushel (~4 dry gallons) of soil mix, more than enough for most home gardeners getting started use a 10 cup measure (I use my large 8 cup pyrex filled to the brim) and mix :

  • 3 parts peat moss (or use Coconut Coir or PittMoss to avoid Peat!)
  • 2 parts coarse sand or perlite
  • 1 part garden soil
  • 2 parts compost
  • 1.5 cups fertilizer (Coleman suggests mixing equal parts blood meal, colloidal phosphate and greensand, you can also purchase a general organic fertilizer like Espoma Garden Tone 3-4-4 or Down to Earth Vegetable Garden 4-4-4)
  • 1/2 cup lime

Mix all ingredients together in a wheelbarrow. Soil blocks need excess moisture for forming a block, add 1 part water gradually to 3 parts mix until it forms a putty like substance which you can form in a ball in your hands. For regular seed trays add a bit less water so soil is moist.

Using your soil mix and notes on timing begin starting seedlings indoors. Plant seeds at the depth directed on the seed packet and keep soil mix moist to germinate seeds.  When you are just getting started with gardening, setting seedlings in a window can be sufficient. As you progress to growing more plants by seed consider using inexpensive and energy efficient LED grow lights on a timer to provide more targeted light to the seedlings for longer during the day. More consistent light for 12-16 hours a day, a gentle breeze from a nearby fan, and stable colder temps (once germination is complete!) such as in a basement, can provide good conditions for strong seedlings and preventing tall leggy stems.  Most plants will grow in their original pot or soil block until they are ready to be hardened off and transplanted. Tomatoes, peppers and larger plants started earliest in the season might need potting up to a larger soil block or pot to enable continued growth.

To harden off your seedlings, about a week before planting outside begin placing plants outdoors for a couple hours longer each day, avoiding direct sunshine in the heat of the day. Work up from 2 hours out in the morning light to a full day outdoors in partial sunlight over the course of the week and then transplant plants into their garden beds, watering well.