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Indoor Seed Starting Tips

Moisture control, proper containers, and good potting mix are key to starting seeds.

Seedlings and SoilIt’s early March and we’re smack dab in the middle of the seed starting season, or maybe just getting ready to start in more northern climes. It seems like a good time to review some tips for starting seeds indoors and growing seedlings ahead of outdoor planting. And while the basics of seed starting are pretty simple, there are always some tried-and-true tricks as well as some timely reminders to make your seed starting experience a worthwhile one. First time seed starter or someone who just wants to review the basics? Try here.

Important Tip: The one thing we’ve found to be most important among many important things when germinating seeds indoors? Moisture control. This means not only controlling the moisture in your starting mix, but providing the proper drainage. And, in the circular, everything-is-related-to-everything-else world of gardening, this means using the right starting mix.

Of course you can buy a good, organic starting mix. We don’t like to use potting soil mixes unless we blend in some of the ingredients — like perlite, charcoal, or coconut coir (we prefer using coir because, unlike peat moss, it’s a renewable resource) — that facilitates good drainage. You can also make your own starting mix. There are several good recipes that involve leaf mold, compost, garden soil, sand, and other drainage facilitators. We usually avoid garden soil. It has a tendency to compact (bad drainage) and may harbor diseases. Of course you can sterilize the soil before you use it, but that will also kill the beneficial microbes and other organisms that will help your plants get off to a good start. And it might make for kitchen smells your family isn’t used to.



Vegetable Seeds

All heirloom seeds offered by Planet Natural are non-treated and non-GMO.

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Planet Natural offers heirloom garden seeds — not the sort you’ll find in box stores — that are non-treated, non-GMO and NOT purchased from Monsanto-owned Seminis. Need advice? Visit our vegetable guides for tips and information on growing specific types.

Best is to make your starting mix with your own compost. A good quality compost — be sure to screen it first — helps with drainage and only gets better as you add other drainage inducing ingredients. Some recipes suggest equal parts compost, vermiculite/perlite, and coir or sphagnum moss, but we like to up the compost ante to three and even four parts compost to one of drainage material. Here’s a simple recipe that’s easy to make. Using compost has the advantage of not having to use fertilizer in a seedling’s early, tender stages when they’re particularly sensitive to burn. And because compost is usually well-balanced, you don’t have to worry about too much nitrogen keeping certain seeds, such as lettuce, from germinating.

Another component of good drainage is the container used to start your seeds. An acquaintance recently remarked about starting seeds in egg cartons, one seed per egg spot. Not only does this make for bad moisture control conditions, it also doesn’t allow proper room for root growth. Make sure your seedling have enough space, both in depth and between plants, for good growth. And make sure your containers have holes in the bottom for drainage. If you’re starting something that will be in its container for a while, say tomatoes (though they’re easy to transplant), you might even want to put some broken pottery shards or pea-sized gravel at the bottom of the container to make a place for extra moisture to drain through.

Once your seeds are planted, covering the flat or container with plastic wrap will help control moisture levels until seedling appear. But don’t overwater!

Keep Records

It’s important to know how far in advance to start your seeds ahead of the date they’ll go out into the garden. The best way to do this is to keep records from year to year. Sure, there are charts that can give you guidance — here’s one designed for zones 5 and 6, with suggestions on how to convert for warmer and cooler zones. Record not only when you start seeds indoors but the dates of last frost and when plants were hardened off and set out. You’ll be glad you did. And don’t forget to label starting pots and flats as to which seeds they contain. Those little seedling will often look a lot alike and you might not be able to identify them until it’s too late.


Once your seedlings emerge they need light. We’ve found that a window sill, even a sun porch, doesn’t provide enough light to grow strong, healthy, compact starts. Use some form of artificial lighting– we especially favor the T5 fluorescent bulbs for the quality of their light, the simplicity in using them, and relative low expense to purchase and operate. Once seedling emerge bring the light as close to the plants as possible. Keep a close eye on growth and move the lights up as they progress. We give our starts 12 hours of light a day.


Seeds need warmth to germinate. That’s why we’ve always recommended a heating mat. But a young, grade-school friend of ours once recommended that we put our overflow tray on top of the refrigerator. He’d been studying energy usage and had discovered that the energy used to cool a refrigerator made for warmer temperatures on his top. It worked! It’s also a good place to let bread dough rise during the cold days of winter.

Once seedling our up and growing, don’t be afraid to touch them. A gentle brushing across the top will result in sturdier stems and hardier plants.

Need more information? Here you go. And here you go again (PDF). Have any tricks, suggestions, or special techniques? Please share them with us and our followers. We’d like to know!

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