How to Start Seedlings When You Live in a Cold House

It is entirely possible (and practical!) to start all of your own seedlings, even if you live in a cold, off-grid house. By adopting a few simple hacks, you can grow vigorous, robust seedlings that will thrive in your summer garden.

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For years, I've been starting all of our own seedlings. It's one of my favorite pre-season gardening projects, and I'm usually looking forward to getting out my seeds long before it's time to actually get them started.

Starting our own seedlings is what my mother always did for our large home garden when I was a kid. So by the time I was an adult with my own garden, I couldn't imagine it any other way.

The other day though, I heard from a reader who felt that starting her own seedlings for her garden wasn't option, because her wood-heated, off-grid home is so chilly during the months of February, March, and April. Those are the months when young seedlings really need to be getting started, to make many crops successful here in our northern climate.

I wanted to assure this reader that even in a really cold house, starting your own seedlings CAN be entirely successful!

My own home here in Maine has been heated with wood for the majority of the time we've lived here, and most people would probably consider my home to be pretty chilly during the winter months.

Indoor nighttime temperatures often dip into the 50s, especially in the main living areas where my seeds are starting.

You do not need a warm house, with nice even temperatures, to successfully start all of your own seedlings at home. Starting robust seedlings of all varieties does take a little extra care and strategy if your house has especially cool or uneven temps though! Here are some tips I've learned over the years for seed-starting success in a cold, wood-heated house:

1. Use mini-greenhouses

One thing that really helps carry some of the daytime warmth into the cold nighttime hours, is the use of small greenhouses. This helps to trap a bit of daytime heat around the seedlings, keeping them from getting quite so cold in the midnight hours.

A "mini greenhouse" can be anything that helps retain warmth and moisture. It can be as small as a clear clamshell package that you'd buy berries in from the store, or as large as an actual walk-in "pop-up" greenhouse that you set up in your mudroom.

A mid-sized solution that works extremely well is to set entire seed-starting flats inside large, clear Sterilite-type containers. With these, I've found that it generally works well to take the lid off once the house warms up in the morning, then replace the lid in the afternoon, well before the house starts to cool for the night.

If your house really gets cold, you might even want to consider using mini greenhouses inside a larger greenhouse.

During a couple of my early years in this house, when I was struggling with a supply of green wood, and the house was really frigid, I actually set up one of those little portable greenhouses that you can find at almost any department store in late winter and early spring.

It stood in the area that's now my office, and it was like a little miracle room of warmth and lovely green seedlings. I could not believe how much warmth it was able to capture and hold in overnight. For those starting a large garden's worth of seedlings, this might not be overkill! For me, it was worth a little re-arranging for a couple of months, so that we could very cheaply grow enough seedlings to supply our 4,000 sq. ft. garden.

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2. Don't over-water

Seedlings that are growing in colder-than-optimal conditions can be more sensitive to high moisture levels. Sitting in soil that's too damp can be a concern.

I've found that when seedlings are both too cold and too wet, they're far more likely to suffer from "damping off."

The fungi, Rhizoctonia spp. and Fusarium spp., along with the water mold Pythiumspp. are the most common pathogens responsible for damping off.

University of Minnesota Extension

If your seedlings start off well, but suddenly bend over near the soil line, with limp, translucent sections of stem, damping off may likely be your problem.

According to the University of Minnesota Extension, "The fungi, Rhizoctonia spp. and Fusarium spp., along with the water mold Pythiumspp. are the most common pathogens responsible for damping off."

These pathogens particularly thrive in cool, moist settings. Thankfully, once your seedlings get a little larger, with stronger root systems and at least one set of true leaves, they're far less susceptible to damping off.

So your mission is get your plants safely through this brief but critical time. You definitely don't want to let your seedlings get too dry, but use caution with letting them sit too wet, especially during the cold overnight hours.

Here are some key tips to keep in might when watering your seedlings:

• Water from the bottom, whenever possible, rather than the top.

• Water only as much as you think your plants will need for a day at a time, rather than really soaking them.

• Whenever possible, water in the morning instead of the evening.

If they can be spend their dampest hours during the warm daytime, then be drier during the night when the soil is coolest, this really helps to prevent damping off.

3. Make sure seedlings have enough light

To quickly grow, and establish strong roots and leaves, your young seedlings need adequate light. Helping seedlings to grow quickly past the danger of damping off, makes abundant lighting critical.

A south-facing window is usually an ideal place for starting seedlings. If you don't have much natural daylight to work with, you might want to consider investing in a grow light.

Because my house is on a southern slope, with many south-facing windows, I've never actually worked with a grow light myself. There are many styles and brands of grow lights to choose from, and some may work better for your situation than others.

4. Heat mats are game-changers

Last year was the first year that I used heat mats under my seed trays, and I really found them to be a game-changer! Seeds germinated in less time, the seedlings put out their first true leaves more quickly, and damping-off was almost non-existent in the flats grown using heat mats.

If you live in an off-grid home and are keeping electricity use to an absolute minimum, they might not be a viable solution for you. They're also about $10 per mat, so if you're starting many, many seedlings, the cost may be prohibitive. BUT, if you're starting just a few flats of seedlings, and are looking for an easy solution to the cold-house problem, heat mats are a great one! In many ways, the addition of a heat mat really can be a silver bullet, to the cold house problem.

I have found that I get the best results by plugging heat mats in at night, then unplugging them during the day.

5. Choose a high-quality, light seed-starting mix

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When other conditions (like warmth!) aren't optimal, soil quality matters a little bit more. I've found that using poor-quality seed starting soil in a cold house is a pretty good recipe for seedlings that dampen off, and that more frequently fail to thrive.

Using a high-quality, lightweight seed starting mix is a key part of having great success with starting seedlings in a cold house. It doesn't need to be expensive, just opt for a choice that's light in weight for the volume of the bag. Mixes that are high in peat or coconut coir tend to be good options.

If a "seed starting mix" seems heavy, is blackish in color, and resembles dirt from the garden, I'd go with a different option. Heavier "potting soil" type mixes can work well once seedlings are strongly established, but to get them past the critical damping-off stage, having a light and sterile mix is a better choice.

6. Adjust your seed-starting schedule

When you're starting seeds in a cold house, some plant types tend to grow more slowly than they would in a warmer environment.

I'm thinking especially of the slow-growing, heat-loving Solanaceae family. I have always found that tomato, pepper, and eggplant seedlings take longer to grow in my chilly house than they would in a warmer setting.

In fact, during the years when I had that mini-greenhouse set up in my office, I did an experiment. The tomato seedlings that I grew inside the greenhouse grew about ⅓ larger, in the same amount of time, than the ones that couldn't fit inside and had to tough it out in cooler temps.

If your house is cold, and if you're not using heat mats, you might want to consider bumping up your seed-starting timetable. I've generally found it helpful to start seedlings that require a long head start, about two weeks earlier than what's generally suggested.

I do this for the Solanaceae crops, as well as any onions, woody herbs (like sage or rosemary), and most slow-growing flowers.

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These are the most important tips I've learned, in my years of starting (many, many!) seedlings in a cold house. Please don't feel that it can't be done!

Starting your own seedlings is a joy, and it's a frugal way to start all the plants you need to supply your own garden, and perhaps even the gardens of friends and family!

With a few easy hacks, and a little extra care, your seedlings can be every bit as robust as the starts you'd buy in a garden center.

Have any lingering questions about starting seeds in a cold house? I'd love to help! Drop your questions in the comments below!

Happy gardening!