Best Time to Start Seeds: How to Start Seedlings

One of the keys to starting seeds is to know the date you plan to transplant outside into the garden. This will need to be after the danger of frost has passed and after the soil has warmed, usually about two weeks after the last frost date.

Plant your seeds indoors five to seven weeks before that date. There is no need to get the seeds started earlier. Doing so will likely result in leggy plants which aren’t desirable.

What you need to start seedlings

• Seed-starting mix, which will give your seeds the best start. Potting soil or soil from the garden can be too heavy. Garden soil may contain pathogens that aren’t good for the seeds.
• Cell trays, small seed pots, or flat containers. You can buy seed-starting cell trays, shallow containers, or small biodegradable pots in varying sizes, or you can repurpose small plant or other containers you may have on hand.* 
• A tray cover or plastic wrap
• A warm spot or a heat mat, and a light source such as a grow light or a South-facing windowsill
• Spray bottle for water
• Seeds

*Wash your containers with a bleach solution (1-part bleach to 9 parts water) or with a disinfecting household cleaner to remove any pathogens. Make sure to punch drainage holes in the bottom. If you wish to grow only a few plants, small biodegradable pots can be a good option. You simply plant a seed or two in each and then can transfer directly to the garden when it’s time. To plant many seeds, cell packs or shallow trays may be useful. Simply start the seeds and then separate and transplant into larger containers as the seedlings grow.

Sowing seeds, step-by-step

1. Dampen the soilless mix and fill containers to within ½- to ¾-inch of top.
2. Plant a couple of seeds in each 2-inch pot or cell. Plant ¼ inch deep.
3. Cover with the soilless mix.
4. Mist lightly with water. Don’t let the soil mix dry out.
5. Cover with tray cover or with plastic wrap; this creates a mini-greenhouse effect.
6. Place in warm location.
7. Keep soilless mix moist.
8. When the seeds germinate and the seedlings appear in 7 to 10 days, remove the tray cover or plastic wrap.

Taking care of seedlings

When the first set of leaves appear (called cotyledon), this is the time to place the trays or containers under grow lights that are about 2 inches above the plants. If you do not have grow lights, place in a South-facing window. Plants will grow toward the light, so plan on rotating your plants every day so they will not lean heavily in one direction.

Water from the bottom. This is easy to do if you set your cell packs or small recyclable containers in a tray that holds water. The plants will soak up the water. Adjust water level as needed so that pots don’t sit in water for a long period of time.

As real leaves appear, after the first set, fertilize with a liquid fertilizer that is diluted to half strength. Follow label directions. Apply every two weeks.

Hardening off plants

When your plants reach about 6- to 10-inches tall, they are almost ready to transplant outdoors, but there is an important step you will need to take first. Even though your plants may have had grow lights or have felt the sun through a window, moving them outdoors can be a shock to them. They need to acclimate to the sun and cooler temperatures over a period of a few days. This is called hardening off and will take 7 to 10 days.

Start by setting your plants outside for only about 30 minutes the first couple of days. Then gradually, over the next 7 to 10 days, incrementally leave them outside for an extra 15 minutes or so each day. Spring temperatures may still be chilly, but the sun is strong, so this step is essential. Spring winds can result in wind burn to plant foliage, so protection from wind is important. Shady areas around your house can be good spots to get them used to outdoor temperatures and light. Another option is to use shade cloths. Shade cloths are available in varying levels from minimal to dense protection from UV light.