6 Tips for Successful Indoor Seed Sowing

by Maria Kreidermacher

One of the things that gets me excited at this time of year is seeing something green, especially seedlings. Of course, the greenhouse is the ideal condition to grow plants, but if you want to grow some early cold hardy veggie seeds to start your garden before you can get into Pork & Plants, you can start some seeds in your home.

Ideally Early to mid-March is the key time in Minnesota to start many cold-hardy veggies but all the way to mid-April works. Look at the crop time on the seed packet to determine when to plant your seeds. For example, many onions are 100 days after transplant, so early March sow, while broccoli can be 50-60 days, so mid to late March. Arugula can be as fast as 40 days, which more often you can direct seed outdoors once the nights are above 40’F but it can be started indoors for an earlier harvest to enjoy that fresh taste of spring.

Heat-loving veggies like tomatoes and peppers are best started in April when it’s warmer and days are longer OR save yourself time and buy larger plants in May from the greenhouse, along with another batch of cold veggies, so you have multiple harvests in the garden!

Without a greenhouse, starting seeds indoors is easiest if you have grow lights and heat mats, like Mom (Joyce) did when we were kids back in the 70’s. Joyce would take heat mats and fluorescent lights out of the hog barn and set them up in our “sewing room,” so that she could start growing veggies for the 1-acre summer garden. We would reuse waxed cardboard milk cartons as seedling trays, which nowadays people online recommend egg

cartons or empty toilet paper rolls. By the early 80’s, it was a family winter project of taking all the milk cartons saved over the year and cutting them off to make plant containers, as you can see in this 1983 picture of me with petunias in milk cartons(on their side) in our first wooden greenhouse Dad (Ed) built.

You too can grow basic veggie seedlings with minimal supplies, as long as you have these key things:

1. Seeds- preferably use organic seeds, especially with vegetables, since you will eventually be eating them and want to know that there’s nothing to worry about. If you’re interested in old heritage varieties, Seed Savers Exchange (Decorah, IA) is a great source.

   
   

   

   
   

2. Soil-less mix- not all soil mixes are the same. Since many seeds can be quite small, typically you want to look for soil mixes specially labeled as germination mix.

   
   

   

   
   

3. Light- an LED grow light for plants is ideal but can easily cost over $200, since the light wavelength is specially geared to plants (often looks pink like our lights in the greenhouse). Typical fluorescent lights are cheap and can be used, but they can cause seedlings to stretch since the light wavelength isn’t specifically for plants. A big southern window can work in a pinch, especially as our days getting longer now.

   
   

   

   
   

4. Heat- ultimately you want the soil warm, which is why heat mats are ideal. If your seedling containers are black, the sun will warm the soil in the container. There are lots of seed starter kits for sale, such as this Burpee kit I bought years ago and keep reusing with new soil. When I need more space for larger pots, I also use a clear plastic tote, placed upside down with the plants on the lid this acts as a mini greenhouse trapping in heat and humidity during the day. The plastic cover/tote can heat up too much during the day, especially with full sunlight, so I crack the lid or take it off entirely once the seedlings are growing. Once the seedlings have multiple leaves, they will stretch less if the plants get colder temps at night 35-45'F. (For cold hardy veggies)

   
   

   

   
   

5. Moisture - Seeds need a moist environment to germinate but read the seed packet for specific recommendations. Rainwater is ideal, but distilled water is the best substitute, because the chlorine, fluoride, etc., from city water could be detrimental to the seedlings. Make sure to keep the top of the soil moist until the seeds are sprouted, a spray bottle works great for this.

6. Food- Since the seed contains all the nutrients it needs to germinate and start growing you will only need plain water. Once the seedlings are up and have leaves, the soil won’t have anything to feed it, which is why you’ll need to add fertilizer to the water. We usually recommend 1 tsp Nature’s Source (all natural) fertilizer per gallon water, but with seedlings, they don’t need as much feed yet, so you should use ½ tsp per gal.

   
   
   
   

Once the seedlings have multiple leaves and roots reaching the sides of the container, they can be transplanted to larger containers indoors. Just make sure to use a fork to gently lift the soil/root ball out of the pot in the new container. Once the nights are above 40’F, you can start “hardening off” the plants outside to prepare them for the garden. To do this, you gradually introduce them to the outdoor conditions by placing them where they get just a few hours of direct sunlight in the morning and shade/filtered light the rest of the day. Then increase the sun a few hours each day over a week's time. If it’s an especially warm day, make sure they are watered in the morning and give them shade over the middle of the day when the sun is the hottest, otherwise, you risk them getting sun scalded or dried out.

If the plants have a long stem between the soil and the first leaves, most veggies can be buried in the ground up to the leaves, which will actually make them stronger, since roots will develop along the stem. Water them in with some fertilizer, so the plant has food to get them growing.

Whether you’re sowing seeds for your garden or as a project with a newbie gardener

(child/grandchild), enjoy the miracle of life!

For more information, check out:

University of MN Extension

Minnesota State Horticultural Society