Seed Starting and Planting

How do I know when to start seeds indoors? Some plants germinate and grow faster than others, and the best time to transplant them outside also varies. For example, tomato seeds are usually planted indoors 6 to 8 weeks before the average last frost. Pepper seeds typically need 10 to 12 weeks of indoor growing time, but because they thrive when transplanted 2 to 4 weeks later than tomatoes, tomato and pepper seeds can be sown at the same time. It may seem complicated, but with a little experience it will become easy.
How long does it take for seeds to germinate? Germination rate varies by plant and with climatic conditions. Most seeds planted in a controlled indoor environment will germinate within 7 to 10 days. Pepper seeds can take longer; placing these in a warm area (on top of a dryer, refrigerator, or seedling heat mat) will speed up the process. Outside, soil temperature is the biggest predictor of germination time. The same bean or squash seed planted in spring soil that is 70° may take a week to germinate, whereas a succession planting in summer soil that is 85° could germinate in 2 to 3 days.
What should I do to keep  my  indoor  seedlings  healthy? Do not overwater; roots need oxygen, too. Turn on a gentle fan to help strengthen seedling stems. Above all, keep plants within a few inches of a grow light. If you find your seedlings growing tall and thin (known as “leggy”) and stretching toward a light source, your plant is stressed for light. This is the most common seed-starting mistake I see, and sadly, once a plant is stressed this way, it’s hard for it to rebound. Prevent this by ensuring your seedlings get plenty of light.
Will my seedlings stay in the original  containers  until  I  plant  them  outside? As a general rule, if the height of the plant doubles the height of the container, the plant needs more room. If this happens and it’s not yet time to transplant, you can “pot up” the plant, which means transplanting it into a larger container. If you used shallow seed-starting trays, you can pot up to a plastic cup with drainage holes.
When potting up, it’s good to use a potting mix instead of a seed-starting mix because plants at this stage can use the extra fertilization a potting mix provides.
If I’m planting in containers, can I start seeds indoors in those containers and later move them outside? In theory, yes, though the size and weight of most containers (and the limitations of indoor grow light space) might make this impractical. Small pots of herbs or lettuce are good options if you want to skip transplanting.
Should I add anything to the  planting  hole  when  transplanting? A common recommendation for years was to add extra fertilizer and compost to the planting hole. A better plan is to ensure the entire planting medium is full of organic matter. This encourages roots to grow deeper and wider, which results in stronger, more resilient plants.
All my seeds germinated! I planted more than I needed; now what do I do? You need to cull extra seedlings. We all hate to do it, but if you skip this step, seedlings will compete for water and nutrients and none will thrive. Take scissors and snip the weaker plant at soil level so you don’t disturb the delicate root system of the remaining seedling. This is necessary for both indoor and outdoor sowings.

Resources

Find your average frost date

The Old Farmer’s Almanac, https://www.almanac.com/gardening/frostdates

Find your local cooperative extension service by zip code

Gardening Know How, https://www.gardeningknowhow.com/extension-search

Find soil-testing labs by state

Gardening Products Review, https://gardeningproductsreview.com/state-by-state-list-soil-testing-labscooperative-extension-offices

Garden tools

Gardener’s Supply Company, https://www.gardeners.com

Seed and plant suppliers

Baker Creek Heirloom Seeds, https://www.rareseeds.com

Seed Savers Exchange, https://www.seedsavers.org

Southern Exposure Seed Exchange, https://southernexposure.com

Territorial Seed Company, https://territorialseed.com

References

Bradley, Fern Marshall, Barbara W. Ellis, and Deborah Martin. The Organic Gardener’s Handbook of Natural Pest and Disease Control. New York: Rodale, Inc., 2009.

Bradley, Fern Marshall, Barbara W. Ellis, and Ellen Phillips. Rodale’s Ultimate Encyclopedia of Organic Gardening. New York: Rodale, Inc., 2009.

Bradley, Fern Marshall, and Jane Courtier. Vegetable Gardening. White Plains, NY: Toucan Books, 2006.

Cool Springs Press. Gardening Complete. Minneapolis: Cool Springs Press, 2018.

Damrosch, Barbara. The Garden Primer . New York: Workman Publishing, Inc., 2008.

Harrington, J. F. “Soil Temperature Conditions for Vegetable Seed Germination.” University of California at Davis. Accessed October 18, 2019.

https://extension.oregonstate.edu/sites/default/files/documents/12281/soiltemps.pdf .

McCrate, Colin, and Brad Halm. High-Yield Vegetable Gardening . North Adams, MA: Storey Publishing, 2015.

Reich, Lee. Weedless Gardening . New York: Workman Publishing Co., Inc., 2001.

Southern Exposure Seed Exchange (blog). “The Major Plant Families in a Vegetable Garden.” Accessed October 22, 2019. http://www.southernexposure.com/the-major-plant-families-in-a-vegetable-garden-ezp-190.html .