How to Start Seeds Indoors

A tray of tomato seedlings

How to start seeds indoors without a greenhouse

This post was updated in January 2022

I want a greenhouse. A greenhouse or a high tunnel, either one. Or a sunroom attached to the south or west side of the house, somewhere I can start seeds early in the season. And to sit in during the winter when it's cold and I want to be "outside."

I've even collected a few windows here and there, and the glass door that we replaced on our home a few years ago, but I don't have enough to build my own greenhouse.

This post contains affiliate links. Read my disclosure here.

I'm even jealous of the cute home-built greenhouse that came with the house our youngest daughter and son-in-law bought. But instead of growing things in it, it houses their kids' outdoor toys.

"No, no!" my heart cries out. "You need to have plants in there!" Oh well, maybe in the future when the children are older she'll discover that she likes growing things. Or maybe not.

If you're greenhouse-less too, you'll be glad to know that you can start seeds inside your home instead. It really isn't that hard, although you might have to rearrange the furniture.

We just have to be be a little more creative when it's time to plant seeds indoors. Let's brainstorm about seed-starting locations, seed starting supplies, and talk about how to start seeds.

Near the bottom of this post I also have some unusual greenhouse ideas that my friends have used, as well as suggestions on how to heat a small greenhouse structure.

In case you're wondering, the high tunnel in the photos in this post belongs to a friend of mine. She got it through an NRCS grant program.

Grow your own garden plants from seed even if you don't have a hoop house or greenhouse.

Starting seeds indoors

Start by assessing locations inside your house that might work.

For instance, we have house cats, and one feline in particular likes to munch on green things. And knock over containers. And dig in the potting soil. 

I used to grow seedlings on the kitchen counter, out of reach of the plant-munching cat, but I had to find a new location when the youngest cat Thor came to live with us. He's not allowed on the counters but I regularly find him up there. (And I'm not happy when I find him up there!)

Which means my seed starting containers have to live in one of the extra bedrooms, where the door is closed to keep the cats out.

Hopefully you don't have plant-munching cats that narrow down your possible seed-starting locations. Lucky you!

Seed-starting containers

You can plant seeds in just about any container, including reused small plastic pots, recycled yogurt cups, homemade newspaper pots, or toilet paper tubes filled with soil. Just be sure to wash reused containers well with a diluted bleach solution.

The containers need to have holes for water drainage, but you can poke holes in the containers if there aren't any.

Small seedling pots made from peat or pots made from coir are also available. These biodegradable pots can be planted in the garden when your seedlings are old enough to transplant, to minimize transplant shock.

Or fill seed starting trays with seed starting mix, and plant your seeds directly in the tray. 

These seed starting kits include plastic containers and humidity domes to go on top. Sprouting seeds love humidity!

Broccoli sprouts growing in a plastic tray

Prepare your seed starting mix

Dirt from your garden or from established containers can contain diseases that may prove fatal to your tiny, vulnerable seedlings. Instead, plant in a sterile seed starting mix to get your seedlings off to the best start.

Before adding the seed-starting soil to your containers, pour it into a clean bucket, add a small amount of water and mix with your hands or a clean trowel. You want the medium to be damp, not soggy, so add water a little at a time, adding more until the mixture is damp enough.

Fill the containers with the soil, leaving about half an inch of space at the top. Tap the container gently on the table to help remove air pockets.

Using peat or coir pellets to start seeds

Instead of containers and soil, you can use peat or coir pellets or discs.

Peat pellets are hard, flat discs that are soaked in water until they swell, then planted with seeds. You can plant several seeds in each disc, or one seed for larger plants such as tomatoes.

Peat pellets are then planted directly in the garden when the plants are large enough, rather than removing the plant and soil from a container and planting in the ground. Using the pellets can minimize transplant shock. 

Some gardeners prefer to use coir pellets made from coconut fiber, which is a sustainable alternative to peat.

Fill a tray or bowl with warm water and soak the flat pellets according to the directions included with the product. When the pellets have swelled completely, remove from the water and let them drain a bit, then plant your seeds in the center hole.

Sowing your seeds

Check your seed packet for the recommended planting depth for each type of seed you are planting. 

Poke holes in the soil-starting medium with a pencil or skewer. Add a couple of seeds, then pinch the soil back over the seeds. Press lightly so they'll have good contact with the soil. 

Label each container with the type of seed and the date you planted them. Don't kid yourself that you'll remember which container holds what, because believe me, you won't!

Mist the soil lightly. 

Cover your planted containers or pellets with a humidity dome, such as the one included with this seed-starting kit, or make your own by placing the containers inside a plastic bag and tie the end shut, or recycle a deli container tray with a clear lid.

Watering your seeds and seedlings

Even watering is necessary for seeds to germinate well, but overwatering encourages mold and will kill your seeds and tiny plants.

Misting with a spray bottle is the safest way to water seeds and seedlings. Adjust the bottle to the finest spray possible, and moisten the surface of the soil. Check your seeds daily to check for germination and mist if the top of the soil has dried out.

Keep your seeds warm so they'll sprout

Warmth is more important than light when you first start your seeds, so find the warmest spot in your home for your seed starting containers.

The top of your refrigerator is a good spot for this first phase of seed-starting.

If your seed-starting location is a bit on the cool side you can purchase a seedling heat mat to use underneath the seed-starting trays.

That dome or lid that you covered your containers with, or the bag you put them inside, provides the humidity that sprouting seeds appreciate. 

While seeds don't need light at first, as soon as the sprouts appear they'll start reaching toward the light, so you'll need to move them to the sunniest spot you can find. 

Once they've sprouted, remove the humidity dome or plastic bag. Too much humidity can cause mildew or fungal problems.

From now on, water the containers from the bottom by adding water to the seed starting tray underneath, or setting the containers in a tray of water. Don't overwater, which can cause mold to form on the surface of the soil.

Plants growing inside a hoophouse

Find the brightest light for your seedlings

If you have a south- or west-facing window - and no plant-eating cats around - plan to house your seedlings there. I moved a card table in front of my southwest-facing bedroom window to hold my seed starting trays.

Of course, if you live in the southern hemisphere, you'll want to use a north-facing window instead.

Seedlings require a lot of light to keep them healthy and prevent them from becoming leggy. If you need more light, you can augment what you have with mirrors. Thrift stores and yard sales are great places to buy inexpensive mirrors, by the way.

Simply place a mirror behind the plants, so that the window is in front of the plants and the mirror is in back, with the plants in the middle. The mirror will bounce the light around and illuminate the plants from both front and back.

Additional mirrors could be placed on either side, so that the plants are surrounded by mirrors on three sides with the window on the fourth side. Or cover sheets of cardboard with shiny aluminum foil if you don't have enough mirrors available.

To keep your seedlings strong, let a fan blow on them at low speed. The fan simulates wind and will help your seedlings grow thicker, stronger stems. 

Using grow lights

If you have a less-than-perfectly-placed window, you can use grow lights to boost the light.

Regular shop light fixtures with fluorescent bulbs will provide plenty of light, or you can buy grow light bulbs.

Start with the lights about two inches above the tops of your seedings. You'll need to raise the lights as the plants grow upward. 

If the height of your light fixtures isn't adjustable, you can adjust the plants' height instead. When the plants are tiny, place the containers on top of something to bring them up closer to the lights. Then move the plants down as they grow taller instead of moving the lights higher.

You can learn more about building a grow light system in this post from Hidden Springs Homestead.

Hardening off your seedlings

Before transplanting your seedlings outdoors, you'll need to harden them off. 

Before moving young plants from a warm, bright environment right to the garden where they are subject to direct sun, wind, rain and other weather extremes, help them to adjust gradually. 

Over a period of a couple of weeks set your seedlings outdoors in a protected place, increasing the time they spend outdoors gradually. Bring them back inside at night and when you're expecting high winds, hail and other inclement weather.

Each day let them remain outdoors for a longer period of time, moving them from shade to sun until they are accustomed to the outdoors. And finally, they are ready to be planted in their new home in your garden.

Unusual DIY greenhouses and heating methods

Still wishing for a greenhouse? Maybe it IS possible.

Over the years I've found some innovative ideas for home-made greenhouses, hoop houses and other structures, as well as how to keep the plants inside them warm.

My gardening friend with the drool-worthy hoop house in these photos uses a heated above-ground swimming pool to provide warmth for her plants. (And for an occasional winter swim too!)

Other methods of heating include:

  • Composting inside your hoop house
  • Housing chickens or rabbits inside a hoop house
  • A concrete or brick floor to capture the sun's heat during the day and release it at night
  • Water barrels (often painted black) inside the greenhouse will also capture and release thermal heat

Another homesteading family I know built a lean-to greenhouse on the south side of their home. The structure was made of 16'x4' wire cattle panels (also called utility panels) with a short end on the ground and the other end attached under the eaves of their home, then covered with greenhouse plastic. The ends were built with wood.

The panels are sixteen feet long, so they were bent into a curve. They were attached to each other along the long sides, and formed a "room" alongside their home. It was sort of "half a hoop house" or a half dome shape.

By opening the windows between their house and the hoop house in the winter, these homesteaders took advantage of their wood stove's heat to keep their plants warm.

I bought a goat from another homesteading family who built an in-the-ground greenhouse attached to their storm shelter.

They'd excavated right next to the half-in-the-ground tornado shelter and poured concrete for the floor and walls that went several feet deep into the ground, with concrete stairs at one end.

This "hole in the ground" was topped with a metal frame and glass windows that let the sun shine in. The greenhouse addition was the same size and height as their concrete tornado shelter, which made it attractive as well as functional.

Plants lined the shelves they'd built along the back wall. On particularly cold nights they used heat lamps (the kind used to keep chicks warm) to keep the space above freezing.

Even without a greenhouse you can start seeds early in the season. No need to buy transplants when it's time to plant.

Starting seeds outdoors

Can't you just start seeds outdoors instead? Sure, depending on what plants you want to grow and where you live.

Cold weather crops can be planted directly in the ground and most of them can withstand a light frost.

You'll find some ideas and inspiration in this post on how to grow food in as little as 3-4 weeks and in this post on growing looseleaf lettuce.

If you need to buy seeds, keep reading for the source I use and recommend.

Cold weather crops 

In general the following seeds can be planted outside around the time of you last average frost date (but check your seed packets for specific details):

Brussels sprouts
Chinese cabbage
Collard greens
Mustard greens
Onions *
Swiss chard

*Onions are usually planted as sets or as plants.

Warm weather crops 

These vegetables are best started indoors as seeds. They can be planted outdoors after all danger of frost has passed. In general, wait until the temperature is above 70° to plant these seeds outdoors or to transplant them into the garden.

Corn *
Sweet potatoes **

*Corn doesn't transplant well and should be planted directly in the ground.

**Sweet potatoes are grown from slips, not from seeds, but the timing is still the same: plant the slips outdoors after all danger of frost has passed. Learn how to start sweet potato slips at home, to transplant outdoors when it's warm enough.

Warm weather vegetable plants take much longer to mature and bear fruit (or rather, vegetables), which is why many gardeners start their seeds indoors as much as six weeks before the ideal planting date - or buy already-started transplants from the nursery.

If you live in a place with a short growing season, you might not have time for some of these plants to produce before your first frost arrives, so choose short-season varieties and/or start your seeds indoors so you'll have a harvest before your season is over.

Frost protection

If you're expecting a late spring frost and have already transplanted your seedlings outdoors, you can cover them to help keep them warm. 

  • Turn a glass canning jar over each plant if they're small. Plastic gallon-size milk jugs can also be used by cutting off the top and turning it upside-down to cover each plant, or cutting the bottom off and setting the top portion on top of the plant. These are called "cloches."
  • Build a cold frame over the plant bed by surrounding the bed with straw bales, then cover the top with re-purposed windows or plexiglass.
  • Cover the plants with a "low tunnel" of frost-resistant fabric, which is also called floating row cover or frost blanket. I made the low tunnel in the photo below from scraps of fencing bent into arches, and covered with fabric. (In the photo I used insect-resistant mesh to prevent cabbage worms but floating row cover can be used instead.)

Homemade low tunnel covered with blue fabric

If you use any of these methods, be sure to uncover the plants before the temperature warms up so you won't "cook" your young plants inside. The heat will build up in there quickly.

Where to buy seeds

Seeds are selling out everywhere this spring. Gardening is enjoying a resurgence in popularity and I am thrilled! I love to see people interested in getting back to the basics and learning old skills.

However this means that the major sources of seeds are selling out online and in stores, and it's harder and harder to find seeds right now. 

By the way, did you know you can save extra seeds that you have left over this year for planting next year? You can!

Smaller seed sellers might be the best way to find what you're looking for. I recommend Mary's Heirloom Seeds, a small company that carries over 700 varieties of open-pollinated, heirloom, non-GMO seeds. I've always been happy with the service and the quality of seeds I've purchased from Mary.

If you'd like to learn more, Mary wrote a guest post here on Oak Hill Homestead. You can read more about Mary's Heirloom Seeds here.

Need more resources?

If you'd like more information on starting a vegetable garden, here's how to build a raised bed garden and how to decide what you should plant

You can test the viability of your seeds with this easy seed germination test to do at home.

Here's where you'll find all of my gardening posts (including some growing guides for specific vegetables).

For more self-sufficient posts like this, subscribe to my weekly-ish newsletter "The Acorn" and join me on FacebookInstagram and Pinterest. I'd love to see you there!

You might think all is lost if you don't have a greenhouse. Here's how to find the best location for starting seeds inside your home, plus some DIY greenhouse alternative ideas.

This post contains affiliate links. Read my disclosure here.

This post has been shared at some of my favorite blog hops.


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