The #1 Seed Starting Mistake: Using Garden Soil Indoors

Garden soil is great for your plants once they’re actually in your garden. It’s a completely different story when you're indoor seed starting. Using garden soil for your indoor seed starting operation is certainly tempting. Why not put all that free soil sitting in your garden to good use? A few shovel fulls is all it would take to fill up those seedling cells. Resist the temptation. There’s no better way to ensure your garden fails before it begins than by filling your tray of seedlings with garden soil. We spoke with Amy Enfield, a senior horticulturist at Miracle-Gro, to learn why garden soil is such a bad choice for indoor seed starting and to find out what you should use instead.

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Compaction Suffocates Seedlings

Garden soil is dense and heavy, which is fine when it's in an outdoor garden. But when you put garden soil into a container it compacts into a brick like state, losing pore space, the pockets of air in soil that seedlings need to breathe and grow. Without those pockets, seeds often fail to even germinate and those that do struggle to grow in the hard soil. "Garden soil is too dense for delicate baby roots," says Enfield. "Even regular potting mix is often too coarse in texture for good seed germination."

Weeds, Fungi, and Pests, oh my..

The soil in your garden is teaming with little baddies that want to destroy your garden, according to Enfield. "(Garden soil) often contains pathogens like fungi and bacteria or weed seeds," she says. It’s hard enough for mature plants to fight off these attacks. Seedlings have no chance. By using garden soil, you invite all of these threats into your indoor seed starting setup, giving your delicate seedlings little hope of survival. 

Poor Drainage Drowns Your Seedlings

Garden soil is designed for an outdoor environment where the wind, sun, and earth all help control drainage and moisture retention. In the climate controlled confines of your home, garden soil quickly turns into a sloppy mess that drains poorly, leading to mold and fungi growth and the dreaded damping off that will quickly kill off your seedlings.

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The Smart Alternative 

Seed starting mix is a far better option than garden soil. Note that it’s called “mix.” That’s because seed starter mix is not soil at all. It consists of equal parts coconut coir (or peat moss) for moisture retention, perlite for aeration, and vermiculite for moisture and nutrient retention. Enfield explains why it’s a much better choice for your seed starting cells than garden soil:

• Superior Aeration: Where garden soil compacts like a brick in a container, seed starter mix stays light and airy. This loose consistency allows oxygen to more easily reach seedling roots while giving them room to spread. "(Seed starter) has a fine-grained, fluffy texture and is free of clumps and twigs so young seedling roots can grow easily," Enfield says.
  
• Optimal Hydration: Seed starter mix has peat moss or coco coir, which act like a sponge, giving seedlings the right amount of moisture they need without drowning them. "It holds moisture while allowing excess water to drain freely rather then leaving the soil wet and susceptible to mold and fungi growth," Enfield says.
  
• Sterile Environment: Seed starter mix is also sterile, meaning it contains no fungus, pests, or weed seed, minimizing the risk of such diseases as "damping off," according the Enfield.

Buy It or DIY It

You can purchase a commercial seed starter at your local home improvement store, or you can make your own on the cheap by buying compressed blocks of cocoa coir, vermiculite, and perlite and mixing them together in equal parts. You can use peat moss in place of cocoa coir to bring down the price even more, but we recommend paying a few extra bucks for cocoa coir. It tops peat moss thanks to its neutral pH, longer lifespan, and superior aeration. 

Using old seed starter is also a no-no unless you sterilize it between plantings by cooking it in the microwave. Unless you don’t mind your kitchen smelling like swamp, skip this step and start with fresh starter soil each year.