Tips for Starting Seeds Indoors

Timing

Find out the average or typical last frost date in your area and count back 8-10 weeks depending on what you want to plant. Sometimes starting too early can result in root bound plants that can require more space than you can give them inside, and starting too late can result in a short to non-existent harvest.

Tomatoes: 6-8 weeks

Peppers and Onions: 8-10 weeks

Squash, Zucchini, Cucumbers, and Pumpkins: 3-4 weeks

For root crops like carrots, radishes, parsnips, etc., it is best to sow directly 2-4 weeks before the last risk of frost.

Soil

A sterile soilless mix like Pete or a coconut core base is best for seed germination, as opposed to a garden soil that can be too heavy for sprouts to find their way to the surface and can also contain pathogens that could be harmful for a vulnerable seedling. Pete pellets or jiffy cubes are a great sterile option. I like using these because they do not restrict or stop root development as fast as a small container. I like these for plants with delicate taproots that don't love to be transplanted. Recycled containers like yogurt and egg cartons are also good, but you have to make sure that they are clean and add drainage holes to prevent them from being oversaturated.

Light

Seedlings require lots of light (14-16 hours of light per day). While a large south-facing window that receives full sun can be efficient sometimes, more often than not, you need to supplement your plants with a grow light. Full spectrum LED lights are a great option. Place them 2-4 inches above the plants canopy to prevent them from reaching for the light and becoming leggy or weak-stemmed. If you are using a south-facing window, make sure to rotate your plants daily.

Heat

A heat mat can be very beneficial for germination, especially for warm climate plants like tomatoes and peppers. Ideal temperatures range from 20 to 27 degrees for consistent germination. Even if you are using a sunny window, you still need to make sure that your room temperature is at least 20 degrees and your window isn't getting too cold or getting a draft from outside.

Humidity

Seeds need high humidity for germination. A humidity dome, plastic covering, or plastic wrap can be an easy way to increase your humidity. The humidity dome should be removed once seeds have sprouted to increase airflow and prevent them from damping off. For germination, most seeds like 70%-100% percent humidity. Once they have sprouted, reduce your humidity to 35%-60%.

Sowing Your Seeds

You should water or moisten your seed starting mix before planting your seeds. As a general rule, you can plant your seeds 2x as deep as the seed is wide. Some smaller seeds like thyme and lettuce can be pressed into the surface instead of being buried. Some bigger seeds with hard or wrinkled coating can benefit from being soaked before planting to soften the exterior and speed germination.

Watering

For germination, you need the seed starting mix to be very moist or wet, but once germinated, you want to allow the soil to begin to dry, but you should never let it dry out between watering. Bottom watering or a spray bottle is key when germinating. Top watering can wash out delicate seeds and often leads to oversaturated soil that can cause damping off or root rot.

Fan

Once the seeds have sprouted and developed true leaves, you can introduce a fan to mimic the wind and help strengthen your stems and prevent them from getting leggy. This will also help with airflow and circulation that will keep your plants healthy and prevent unwanted pests.

Hardening Off

This is a very important final step to get your seedlings ready for the real world! This step often gets overlooked when the risk of frost is over and people bring their healthy babies outside in full sun or into the greenhouse. Hardening-off is when you slowly acclimate your future vegetables or flowers from inside to outside. This requires introducing your plants to the sun and wind slowly over the course of 1-2 weeks. Start by placing your plants in a sheltered area outside without full exposure to the sun for 1-2 hours. Each day increase the time, wind, and sun exposure by an hour or two until night temperatures are consistently above 10 degrees and when your babies are ready for full sun exposure and wind.