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The SRSC Guide To Indoor Seeding

Ooh! Ooh! Are you itchin’ to plant some seeds? If so, you are not alone! Gardeners across the region are starting to dream of spring (even where there is still feet of snow on the ground!). So while you’re waiting for the thaw, here are some tips to set you up for success in getting a jump on the season by starting some of your seeds indoors…

Materials you will need:

Containers Truly, you can use almost anything as a pot to start seeds indoors. Egg cartons, yogurt containers, you name it! Some folks even make pots out of newspaper. If you decide to use a container that doesn’t drain, be sure to put holes in the bottom so water can drain. Drainage is important. Like you, your plants are not going to want to be hanging out in stagnant, standing water—yuck! Regardless of the pot you’re using, make sure it’s clean when you go to plant into it.

Potting Soil I’ll be honest and say that most of the seed starting supplies a garden center might try to sell you aren’t necessary for starting and growing healthy seedlings. But potting soil is a notable exception. You definitely want to start with a sterile potting mix or seed starting mix, rather than trying to use soil from your garden to start plants indoors. While garden soil is wonderful in the garden, when you bring it inside and cram it into a little pot, it isn’t happy. It is too dense and makes for crappy plants. So, invest in some sterile potting mix. Some folks use a separate seed starting mix for seeding, and then transplant their starts into bigger pots with potting soil once they’re grown, but I don’t bother doing that. I start all my indoor seeds directly into potting soil with great success. The key is to choose a potting soil that doesn’t have synthetic fertilizers added to it, as those can burn young seedlings as they are sprouting. I like Gardner & Bloome’s potting soil, but there are lots of other brands and your local nursery can help you choose one that they carry.

Light Light is another thing you can’t skimp on if you want to grow healthy plants. Even a sunny, south-facing window won’t give you enough light if you’re starting your seeds in February, when we are getting about 11 hours of daylight every day, give-or-take. Too little light and your plants are going to get spindly and leggy as they grow toward the light. This makes them weaker and less fit to thrive when it’s time to transplant them outside. The best thing you can do to grow healthy starts is to invest in a shop light or two that you can hang directly over your seed starting area and adjust its height as the plants grow. The bulbs don’t have to be anything special for growing—just plain old fluorescents are fine—but you want to get them as close as possible to the plants as they grow. I aim to put my lights no more than 6” above the tops of my plants. I wait to turn the lights on until my seeds are starting to sprout. As the plants grow taller, I raise the level of the light up inch by inch, so they never have to reach far to get to the light. I like to put my lights on a timer so I don’t have to worry about remembering to turn them on and off, and I keep lights on my indoor plants for 14 hours a day.

Water It goes without saying that seeds need water to sprout and plants need water to grow. However, I would venture to say that the biggest challenge beginning indoor seed-starters face when it comes to watering isn’t watering their plants too little—it’s watering them too much. It’s understandable…we all want to be good caretakers for our new little baby plants. However, overwatering your plants can lead to damping off, a fungus that thrives in overly wet conditions. If you’ve ever come to check on your plant babies only to discover that they’ve fallen over looking like someone has come and pinched or cut them off at the stem a half-inch or so above the soil, your plants have fallen victim to damping off. When you first plant your seeds, the soil surface should remain moist so the seeds have enough water to germinate. But once they’ve germinated, it is a good idea to let the soil surface dry out between waterings. Often the surface of the soil dries out but the soil underneath is still wet, so making sure the surface is dry before watering your plants again is a good way to avoid overwatering. This can sometimes take several days, especially when plants are small. So don’t worry! You’re not a bad plant parent if you don’t water your plants every day when they’re young! As they grow bigger, they will need more water. In every stage, let the soil surface be your guide. When it’s dry, give them some water. When it’s wet, don’t.

SEEDS! How could we forget the most important part?! The SEEDS! For a list of seeds we start indoors, including ones we start early (like Feb-March) and ones we start indoors a bit later (like March-April), check out this blog post. Follow the directions for planting on the packet. Some seeds need light to germinate, so simply press them into the top of the soil and keep them moist until they germinate. For everything else, plant at the correct depth. Planting seeds too deeply can cause them to rot before they can push their little seed leaves (cotyledons) up through all the soil on top of them. Generally, smaller seeds are planted more shallowly than bigger seeds.

Additional tips:

*Don’t start your seeds too early! I know, you’re itchin’ to get moving. But plants that are started indoors too early often don’t perform as well when they’re finally able to get outside into the ground. Folks always want to start their tomatoes in January, but then they’ve got to figure out how to keep the plants healthy inside as they grow, for over four more months before it’s safe to plant them outside! We start our tomatoes in mid- to late-March, 6-8 weeks before we transplant them outside around Memorial Day. There are plenty of seeds you can start indoors earlier, like onions, leeks, shallots, and even greens like lettuces. These cold crops are frost-tolerant and they can be transplanted outside even when it is still freezing at night, so you can tickle that green thumb itch with cold-hardy starts first, and wait until closer to your area’s last frost date to start frost-sensitive crops.

*Eschew the “mini-greenhouse-of-death” a.k.a. “seed dome” Often folks will buy indoor seed starting kits that come with a plastic dome you put over your tray of seeds so it acts like a little greenhouse. I do not recommend this, for many reasons. Now you’ve trapped the water inside this thing and created the perfect habitat for that damping off fungus to thrive. Also, you’ve now blocked your easy view of your seedlings as condensation builds up on that dome, making you less capable of recognizing problems with them at a glance as you happen by. And of course, that one extra piece of plastic is gonna push the planet over the edge into climate catastrophe, break down into microbeads that kill sea turtles, and end up in that monstrous island of floating garbage in the ocean…so save everyone the trouble and forego the mini greenhouse of death!

*Heat mats are optional A heat mat is another thing you might be sold as a beginning seed starter. And while it is true that some heat-loving crops like peppers need warm temperatures to germinate (like, soil temps above 70 degrees), most crops will germinate just fine if you’re starting them inside your house. Consider putting your pots of seeds of the few things like peppers that do need warmer temperatures to germinate on top of your water heater or refrigerator, which both generally give off a bit of heat.

*Rustle ‘em a bit! Your seedlings will be stronger if they get a bit of wind on them as they grow, to strengthen their stems and help them survive in the “real world” once they get out into the harsh out-of-doors. If your seed starting area isn’t drafty (which I hope it isn’t!), you can help toughen them up by gently running your hands over the tops of them as they grow. If you are a cigarette smoker, be sure to wash your hands with soap before touching any of your nightshade/tobacco family crops (tomatoes, peppers, eggplants, tomatillos, ground cherries), because cigarettes can transfer tobacco mosaic virus to your hands and you can spread that to these plants who are also susceptible to it.

Harden them off before transplanting outside After the relative luxury of your indoor spa, your plants are going to need to toughen up before they can survive in the garden, with its relentless sun, intense wind, and cycles of hot and cold. It is a good idea to introduce your coddled babies to the great outdoors in short spurts. For several days before you’re going to transplant them into the garden, leave them outside for a few hours, in the shade on the first day or two, and then gradually into more sun on the third day. Bring them back inside at night, or put them in a cold frame with the lid on. After a few days of doing this, they will be ready to transplant outside. 

We hope these tips bring you grand success with indoor seed starting. And if you’re feeling nervous, take comfort….even the venerable Christopher Walken is nervous about starting plants indoors...