Starting Seedlings for Beginners

When I first started flower farming, I had an image in my head that I would be out in my garden tucking each little seed into the soil. I had a rude awakening when I realized that most seeds would need to be started indoors before spring.

In fact, Erinn from Floret Farms starts 90 percent of her cut flowers from seed! Goodbye dreams of tucking each little seed into the garden outside…


If you want to know when start your seeds, you need to know your last frost date. In Lehi Utah our last frost date is around Mother’s Day. The most reliable method for pinning down your last frost date is by asking your neighbors or local nurseries.

Once you know your last frost date, count back the number of weeks your seed packet says to sow indoors.

For example, I needed to start my Snapdragons indoors. The packet says to sow them 8 to 10 weeks before the last frost of the season. Since the last frost date in my area is around Mother’s Day, I started my first round of seedlings the first weekend in March.

If you plan on succession planting, then you will also need to know your first frost date. You can find more info on succession planting in my upcoming post “How to Make a Succession Planting Schedule.” 

Homemade seed staring mix.


You could start seedlings on a south-facing windowsill in your home. However, the healthiest plants are achieved by three basic components: (1) seedling soil, (2) lights, and (3) heat mats.

Of course, a heated greenhouse is ideal, but that is not the most affordable option for us garden peasants just starting out.

I am a thrifty person and researched quite a bit before deciding on my own seed starting station to make at home. Below is a list of materials that I used:

I’ve also seen home gardeners recycle used milk jugs outside to start seeds or clear tubs! That would be the cheapest method.

Most seedlings should be germinated on heat mats since the ideal germination temperature is 70F. (There are some exceptions like Snapdragons that prefer lots of light, but slightly cooler temps.) Your house may be 70F, but your soil is actually 10F degrees or more cooler, hence the heat mats for germination.

Heat mats are not necessary after germination.

They will also need grow lights (unless it is specified that they prefer darkness to germinate). I have my setup in a room with a south facing window and I have a timer that turns the lights on for 14 hours a day starting at 7am.

The lights should hang three inches from the top of the plants (any lower and you risk burning the leaves). You will want a setup that allows for adjusting the lights as they grow.

I experimented with grow lights vs shop lights (GE Daylight T8 bulbs) and found little difference. I prefer the shop lights because they cover more area for cheaper.

You will want four bulbs across for best results (I learned this the hard way).


I started seeds indoors following the Floret Farm method found in her book or on her blog post here.  Rather than retype those instructions, I want to focus on things that were not clear and that I had to learn by experience.

One of the things I have found frustrating about starting seeds is finding an affordable and easy to find seedling soil.

I tried the basic Miracle Gro Seedling Soil first and when that failed fantastically…I tried Epsom mix and Black Gold mix. So far my results have been best with Black Gold.

UPDATE: This year I trying a homemade seed starting mix. This recipe is specific to soil blocking, but you could google others for cell trays.


You’ll find that each seed has specific seed starting instructions on the back of the packet. One may say the seed needs light to germinate, while another seed may need absolute darkness to germinate.

Quick Tip: If you want more specific instructions for a type of seedling then Google the variety + culture sheet. For example, “snapdragon culture sheet.”

To complicate the matter further, the packets will show different germination rates. This is the number of days the seed is expected to take to sprout.

You’ll want to keep seed types separate in their own cell blocks/soil blocks or at least group seeds with similar germination methods and rates together in cell blocks.

Humidity domes typically come off once 50 percent of the seeds have germinated. Once germination takes place (or once you see a set of true leaves) you can start fertilizing to boost growth.

Homemade seed starting recipe.


Below are a few of the common mistakes to avoid when starting flower seedlings indoors:

  1. Top watering: You will want to bottom water your seedlings using the trays that come with the cell blocks. A common mistake is watering seeds from the top, which will flush the tiny seed away.
  2. Shocking transplants: When you are ready to transplant your starts outside, you will need to follow the “harden off” method. This basically means you need to get the plants used to their new environment a few hours at a time before planting them outside. Set plants outdoors for a few hours, slowly increasing the time they spend outdoors before transplanting into the garden. Start this process about a week before you want them outdoors permanently.
  3. Plants becoming root-bound: This happens when your plants grow too big for their containers. I just sowed my Snapdragon seedlings in the 72-cell block size, then realized they will need to be transplanted into larger containers in 3 to 4 weeks before transplanting them outside. Make sure you read the back of the packet carefully to avoid needing to switch your starts to different pots half way through the growing process. Floret Farms says 72-cell and 50-cell flats are her go-to container sizes.
  4. Seedling soil should not have fertilizer: I guess this was my mistake with the miracle grow seedling soil. Seeds don’t need fertilizer until they have true leaves. Seedling soil with fertilizer will launch them into growth resulting in leggy plants that fall over. Many growers prefer to make their own mix for this reason. Once plants have germinated, you can start using a liquid Seaweed and Fish Emulsion fertilizer. To combat leggy plants, you can put a fan on seedlings to encourage thicker stems.
  5. Over or under watering seedlings: I am still figuring out the exact science to this. I had some beautiful eucalyptus starts that suddenly shriveled on me. I still don’t know if it was over or under watering! I am thinking under watering….

It is amazing how long it takes to write each post with two rascally kids climbing all over me. However, I do my best to include details (even if it means admitting how much I failed at the beginning). If you can, I would really appreciate it if you left a comment below. It makes me happy to know someone is out there and it gives my website a boost. Happy gardening!