How to Start Seeds Indoors

Lettuce in deck boxes, May 27

For northern gardeners, many plants cannot be grown from seeds planted directly in the garden. Our growing season is simply not long enough. So, if you want to grow tomatoes, peppers, or other longer season crops you have two choices: Buy the plants as transplants or start seeds indoors.

When to Buy Transplants

If you are growing just a few plants, starting seeds indoors may not be worth the time and expense. In that case, wait until May (even late May) and buy plants from a reputable nursery, the farmers’ market, or get them from a friend who starts seeds indoors. Then, you can plant them directly in the garden or a container and wait for the magic to happen.

Seed Starting Set Up

Unless you have a really sunny south/east facing window, there is probably not enough natural light in your home (especially in Minnesota!) to start seeds without lights. The picture is of my set up: a wire shelf and two florescent light fixtures with regular bulbs set up using S hooks and chains so they can be raised as the plants grow. Your set up does not need to be fancy. However, you will be a much more successful seed starter if you add to your set up a timer, so the lights go off and on at the same times every day, and a small fan set on low. The breeze from the fan helps prevent fungal diseases and it mimics the kind of air movement your plants will experience outdoors. I have never used one, but other expert seed starters recommend a heating mat under the seeds during germination. If your seed-starting location is cold, this might be a good idea. For a few more tips on seed-starting, check out this post or this one from my blog.

Containers, Soil, Seeds

You will also need containers, sterile potting soil, and — of course — seeds. I buy a good soil mix specifically for seed starting. For containers, you can collect yogurt cups, buy peat pots, make your own containers using newspapers, or buy a tray with lots of cells for plants. I use a mix of recycled materials, peat pots and a tray with cells. As long as the containers have holes for water to drain through, they should be fine. Also, it’s worth the effort to organize your seeds according to when they should be started. My system is a simple plastic container with markers for when the seeds need to be started.

Germination and Timing

You want to start your seeds with enough time for them to be sturdy seedlings when it is the right moment for them to go out in the garden. Your seed package will tell you how many weeks before or after your “last frost date” you should plant your seeds. In Minnesota, figure May 15 for the last frost date, and you will be safe.

When it is time to start the seeds, dampen your potting soil. I put some in a bucket and get it pretty wet, then add more potting soil until it’s like a wrung out sponge. Definitely wet, but not soaking. Put the soil into your containers, and add the seed according to package directions. Some seeds just need a little soil on top of them, others need to be an inch or so under the soil. All seeds benefit from soil contact so give them a little shove so they are touching the soil.

Next, cover the tray or cups with loose fitting plastic wrap and put them under the lights with the lights just an inch or two above the tray. Set the lights to be on about 15 hours a day. In a few days to a couple of weeks, you will see little seedlings emerging. Take off the plastic wrap as soon as the seedlings are up.

Monitor the Seedlings

Now comes the fun part — watching your little baby plants grow. As your seedlings grow, you will need to do just a few things: put the fan on for breeze, raise the lights as the plants get bigger keeping the lights 2 to 3 inches above your plants, and depending on the kind of seed-starting mix you used, add a bit of fertilizer. If your seed-starting mix has fertilizer in it, don’t add any. Your seedlings should be fine.

Potting Up

After three or four weeks, some of your seedlings may need to be “potted up.” That simply means moving the plants to a larger container. Plants such as tomatoes and peppers benefit from a little extra room for their roots. I usually use 4 inch pots for potting up. To pot up, put a little damp seed starting mix or potting soil in the bottom of a 4-inch pot, gently remove your seedling from its first container or seed cell (a baby spoon works well or just squeeze the seed cell to release the plant). Place it carefully in the pot, and gently add additional soil around it. Tamp the soil lightly to ensure good contact between the roots and the soil.  Put the new pot back under the lights.

Hardening Off

Eventually, the days will warm up and it will be time for the plants to go out in the garden. But since they have been indoors, a sudden adjustment to bright sun, outdoor winds, and cool nights would be a bit of a shock. So, the idea is to gradually acclimate your plants to the outdoors over a period of a week to 10 days. Start by setting your plants out in a sheltered location (I use our open front porch) for a couple of hours, preferably on a cloudy day.  Gradually, increase their exposure to light and wind before transplanting them in the garden. An alternative to hardening off is to set plants in a cold frame or use a product such as Wall-o-Waters to protect them. Because wind is a big issue where I live, I sometimes plant transplans out with a cardboard milk carton (cleaned, top and bottom removed) around it. This keeps them from fainting in the wind as they get their roots established.

Don’t Rush It

One last thought on seed starting in the North: Don’t rush plants into the garden. I’ve had much better luck with tomatoes planted out on June 1 than those planted on May 1. Weather in Minnesota in spring is unpredictable at best — 80 one day, 40 the next — give your seedlings the benefit of a few more days under the lights rather than rushing them into the great garden unknown.

9 thoughts on “How to Start Seeds Indoors

  1. Hi Mary!! Did I read somewhere that you are from Lonsdale, MN? I live in Lonsdale and I was intrigued by your blog. I am not new to gardening but have always been a terrible gardener. I have recently stumbled on a “new” way of gardening and I am looking for clean hay. I loved your hay bale idea and want to try it. Just a few weeks ago, I was thinking of diminshing my garden now I want to convert most of my yard into one big garden!!! I have never been so excited about this!! I would love any tips you can give and if you are a fellow Lonsdalian, I woul dlove to meet you and see your garden. Michele 🙂

  2. I live in Vermont and picked up a greenhouse frame at my local “transfer station” ( town dump) for free. Had to save through the winter last year to buy the plastic sheeting to fit it but it was worth it to grow tomatoes and peppers like I have never grown before. : ) My questions are about using the greenhouse all year to grow dwarf fruit trees like cherries, pears and black currants. Our intention is to leave them in there all year as we are renters for the moment and don’t want to permanently install fruit trees for my landlord LOL. We get below zero here in zone 3 for a few weeks in January and below freezing for most of the winter. We have tracked the temp in the greenhouse to be at least 20 degrees higher than the outside, mostly due to the lack of wind in there. What are our chances of success? Dwarf fruit trees are not cheap so any help you can give us? thanks : )

  3. Dianne — You are a little past my experience level with this question. There are cherry, currant and even pear varieties that can survive in zone 3 outdoors, so they should have no problem getting through the winter in a greenhouse. If you left them in the greenhouse all year, I would be concerned about whether they would get pollinated properly (though I’ve seen examples of trees in containers on wheels that go in and out of protected areas.) I would check out your idea with a local nursery that carries lots of trees and see what they say. You also might want to find Lee Reich’s books on growing fruit. (He’s a regular contributor to Northern Gardener and a very reliable source of information.) Good luck!


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