Updated: Aug 8, 2019
There are many reasons to start seeds indoors, not least of which is a way to cure spring fever! As well as an economical way to garden, you will get to witness the miracle of seed germination and it is a great teaching tool for kids. Our advice is to start with a few types of seeds; going overboard can overwhelm both your energy and your indoor space.
Getting Started The first thing you will need is seed. The seed packets themselves are full of information, from planting depth and spacing, to germination times and harvest dates. You can save leftover seeds in the packet if kept in a dark, cool and dry place. The success rate lowers the longer you keep them, we recommend that after 2 years you start fresh.
You are going to need an area where the whole process will take place. Keep in mind that the ambient temperature should be between 65 and 70 degrees. If you will be using artificial light or a heat mat, access to power outlets needs to be a consideration as well. Different seed types have different germination and growth rates. If you want to transplant your seedlings outdoors after the last frost, this means starting seeds at different times. Check the directions on your seed packets, since every type of seed has a unique set of requirements.
Clean Containers & the Right Soil It is important that the containers for seed starting be very clean. If you are reusing plastic seed flats from last year or if you are using saved food containers (yogurt cups, salad bar boxes, etc.) use a mild bleach solution to disinfect them. All containers must have holes in the bottom to allow drainage – seeds want to be moist not soaking wet, like a wrung-out sponge.
We recommend that you use a watertight seed tray with a clear fitted dome that keeps the 4 packs or pellets upright and regulates the humidity around the seedlings. We suggest using either a soil-less seed starting mix or compressed discs called peat (or Jiffy) pellets. When warm water is added to the discs they expand into netted seed pots. Both options are light enough to allow baby roots to grow and are sterile, which reduces disease in your seedlings.
Sow the Seeds Fill your clean containers with a moistened soil-less mixture, to about ¾ full, tap the container on a hard surface to settle the soil, or prepare your peat pellets by soaking them in warm water. Using a pencil point, or toothpick make one small hole in the soil and place several seeds (at least 3) in each container or cell. Check your seed packet, and follow the soil depth instructions from there. Label the pots or trays so you remember what is what. You can use something as sophisticated as plastic plant labels or something as simple as a wooden craft stick. The purpose is the same; you just want to make sure that your plants are labeled. On the plant tag, write with a permanent marker the name of plant, date planted, and, once they sprout, the emergence date. Place the seeds in a spot with moderate light – not in direct sunlight. Normal household light will be sufficient in most cases. Some seeds require darkness during germination, which will be indicated on the seed packet. In this case, simply cover the container with a piece of cardboard.
After you have sown your seeds, it is time to give them some water. This can be tricky, especially for the surface sown seeds, as they tend to float. We recommend that you use seed starting trays that come with the cell flat, a clear cover and a bottom pan that you can partly fill with water and let the moisture soak up from beneath. If you don’t have those, use a misting spray bottle and go slow. At this stage you’ll want to keep the seeds moist so check them often and keep them covered with a lid or some plastic until germination.
From Seeds to Seedlings Your seeds will germinate best if you can maintain a soil temperature of 60 and 75 degrees. Heating mats can aid in this. Heat mats provide low, continuous, bottom heat. Cover your containers with plastic wrap or use the domes supplied with seed flats to keep the soil from drying out too quickly. Check your containers once or twice a day and mist them with warm water as necessary.
When your seedlings emerge and the first leaves are opening it is time to remove the heat mat (so you don’t bake the little guys) and give them more light. They need about 16 hours of bright light each day. That means a sunny window is less than ideal since there is not enough sun during short winter days. Most gardeners find that placing the plants under grow lights works the best. Bulbs should be placed several inches above the seedlings and raised as the plants grow. If your seedlings start to get stretched and spindly, it might mean that the light source is too far away.
You may now notice that some of the seedlings are not as strong as their container mates. The weakest and thinnest need to be cut (with sharp scissors no pinching) so the stronger ones can continue to grow at full strength. There is no sense in attempting heroics to rescue the weak seedlings, as their chance of surviving the move to the garden is slim at best. Thin to 1 or 2 plants per cell.
Caring For Your Seedlings You do not need to use fertilizers during germination as all of the necessary nutrients are already in the seed itself. Fertilize after true leaves come, usually the second set of leaves. When you fertilize your seedlings you need to remember that they are babies and you cannot give them adult food. You can burn the tender seedlings. Use a diluted (50%) fertilizer that has a low N-P-K number (this number relates to how much nitrogen, phosphorus and potassium are in the fertilizer). As the seedlings get bigger they will need to be moved to bigger pots in order to keep their growth momentum going. Handle seedlings by the leaves or soil only, not the tender stems. Use potting soil mix, and gently firm the soil after planting. Water immediately and put back under the lights. In about the middle of May or when nights no longer drop below 40°, you need to prepare your plants for transplanting outdoors by hardening them off. This is to be done gradually by introducing them to the outdoor elements. Place plants outside in a wind-protected, shady place for a few hours a day. Increase to full sun over the course of a week if seedlings are to be planted in the sun. You are now ready to plant outside!