Seed starting indoors is a great way to get a jump on the season and enables us to put small plants in the ground once we are past the last frost date in our area, resulting in flowers earlier than if we had waited to directly sow the flowers instead. This is especially important for growing flowers that have a longer time between planting and harvesting. In addition to getting a jump on the growing season, there are also lots of seeds that either require light to germinate or are really small and could easily get washed away with a heavy spring rain. Planting these seeds indoors gives us much more control over the growing conditions and gives us a substantially better germination rate. Each year I generally start seeds indoors around the first week of February, but begin the majority of my seeds around March 1. Seeds that I sow indoors include: snapdragons, feverfew, rudbeckia, marigolds, hibiscus, statice, jewels of opar, scabiosa, and gomphrena.

Soil Blocks vs Trays

Over the years I have used 50-cell and 72-cell trays, as well as soil blocking to start seeds indoors. Both have their pros and cons, and the approach we take varies from year to year. This year we will primarily use soil blocks, but I will still plant several fast-growing varieties in trays so I don’t need to pot them up before planting out.

Soil-blocking - I did this for the first time last year, and like a lot of things about it.
- Pros: Space saver! This was a MAJOR reason I tried this out in the first place. I can fit 180 plants in a 10”x10“ tray. The soil blocks are also very quick to transplant out in the field.
- Cons: Making the soil blocks takes a lot more time then simply filling a tray with soil. I also found that some of the varieties I planted, like Hibiscus, grew so quickly that they had to be translated into 50-cell trays before getting planted outside. If I had initially planted them in a 50-cell tray, I could have saved myself the time it took to move them up to a larger container before planting them out in the field.
50-Cell or 72-Cell Trays - These trays are 10”x20” and great for planting out larger plugs or being used with fast growing plants
- Pros: These trays are very fast to fill with soil and I don’t have to worry about transplanting plugs to a larger size cell before they are ready to be planted in the field.
- Cons: Each tray is 10”x20”, which means that a 50-cell tray takes up the same amount of space as 360 soil blocks. I would need 7x more space if I solely used 50-cell trays as opposed to soil blocks. Additionally, trays cost money and are a less environmentally friendly option.

Indoor Growing Setup

When I first started growing seeds indoors, I was overwhelmed by trying to figure out what type of lights were needed and how expensive it would be to get enough specialty “grow” lights and heat mats. However, with some experimenting, I realized that an indoor grow setup didn’t have to be expensive or require lots of fancy equipment. Our current grow setup is simple and fits in a 2’x4’ footprint in our unfinished basement. To start our seeds indoors we use:

4’-wide metal shelving unit
4' LED lights with an optional on/off timer
Thermometer/Humidity Gauge
Soil blocker and Cafeteria Trays or 50-cell trays
Labels and Markers
Water sprayer/Mister
Sterile Seed Starting Mix
Seeds
Vermiculite (optional)

Starting Seeds Indoors

The first thing to do before getting those seeds started is to find a place to keep them while they are growing. I try to find a spot in the house that averages around 68 degrees and has access to electricity. Pre-kids this was our dining room table. Last year we moved this to the office behind a closed door to keep the trays safe from little hands, and this year it is down in the basement. We have a 2’x4’ metal shelving unit with four shelves. Above each shelf we have a 4’ LED light that we bought from the hardware store and have it hung 6” above the trays. If you use CFL or other types of grow lights, those will need to be hung 2” above the trays. Once setup, it’s time to start seeds.

I prep all my soil blocks or 50-cell trays in one go using moist seed starting mix. I drop 1-2 seeds in the center of the cell or soil block and sprinkle with vermiculite. Everything gets a good mist of water and is then placed under the grow light. I keep the grow light on for 12-14 hours a day. Last year I decided to put the grow lights on a timer so I didn’t have to remember to turn them on or off every day and am definitely doing that again this year.

Once the seeds are sown it’s important to keep the soil moist until the seeds have started to germinate. I also aim to keep the humidity around 70% throughout this process. Some do this by covering trays with plastic domes or plastic wrap. I have also run a humidifier in the room to maintain the humidity too. I check the soil blocks twice a day to make sure everything stays moist. Once the seeds have germinated, I remove any coverings to allow for better air circulation. As the seedlings get bigger and we are closer to transplanting to the field, the trays are set outside during the day to harden off. Once the weather is sufficiently warm, the seedlings are planted out in the field.

Seed Starting Indoors