Do you ever find it frustrating that the most expensive part of starting seeds is… the dirt? Seed trays are cheap, heat mats are cheap, even high quality seeds are cheap! Don’t believe me? Here’s the actual cost breakdown from my most recent round of seed starting:

  • $16 for 10 seed trays of 72 cells each (which is overkill for most gardeners by far)
  • $24 for twelve seed packets (planted across two trays with tons seeds left over to store)
  • $6 for a seed heating mat (bought on sale, but there’s always one on sale on Amazon)
  • 0$ for water as I just catch a little extra from the shower and seed trays need very little by volume
  • $1 for a propagation tray (just a random flat plastic bin lid from Ikea)
  • $30 for two 8 qt. bags of organic seed starting mix (which I didn’t actually buy because that’s crazy)

Which is why I used a single very large, very affordable bag of organic potting soil mix from the local hardware store to fill all my seed trays instead. I even have leftovers to use for grow bag projects. With plenty of experience skipping the pricey seed starting mix, I can happily pass on that the answer to our original question is “yes, you can absolutely use potting soil instead of seed starting mix to start seeds in trays.”

There is however no denying that seed starting mix does result in a notably higher germination rate. Luckily, we can close at least some of that gap cheaply and easily. Try these two strategies for improving your potting soil first before packing it in your seed trays.

Sift Your Potting Mix

The biggest issue with potting mix for seed starting is the presence of larger materials that will obstruct your seedlings. Sticks aren’t an appropriate substrate if the goal is to maximize germination, which is why seed starting mixes are made of much, much finer soil particles.

To fix the issue, grab a coarse kitchen strainer, some hardware cloth, a section of poultry fence, or even a colander with large holes and sift the potting soil first. I’m always a little shocked at how effective this is at creating a finer mix for my seed trays with 30 seconds effort. Don’t forget to reuse the wood chips and other larger materials as mulch or fodder for the compost heap.

Mix Coco Coir into Sifted Potting Mix

The other issue with potting mix for seed starting is that it’s hard to water correctly for germination. It is not exactly fluffy stuff, which makes it easy to overwater, wash away the seeds, and dry out too quickly.

I’ve found the easiest remedy is to mix in some coco coir at a ratio of about one part coco coir to three parts sifted potting mix. Like the potting mix, coco coir is much cheaper to buy at the hardware store than online - I can usually grab a small bag (which is plenty) for a few dollars.

Happy Planting!