I’ll admit it. I’m itching to start playing in the dirt. That’s right, with spring right around the corner, this gardener is ready to play! Lucky for me, winter is pretty much gone here, and it’s time to start seeds indoors.
Starting seeds indoors is a great way to get a jump-start on your garden. Many plants need more time than what nature gives us to produce big harvests. But you can take advantage of the perfect growing conditions INSIDE your home, before it’s warm enough outside.
But how do you start seeds indoors? That’s a great question, and one that I’m going to do my best to answer for you!
Let’s start with the basics:
What plants do well when started as seeds?
While some plants do best when started in seed pots indoors, others should be direct-seeded when the weather is warm enough. It’s best to follow the directions on the back of the seed packets as to whether you should direct sow or start indoors. As a general rule, you should take into account how long the plant takes to produce a harvest, and figure out how long of a growing season you have.
To determine how long your growing season is, you can go to Almanac.com and put in your zip code in their frost dates calculator.
For example, most tomatoes need at least 100 days of growth to get a good harvest. My growing season is 149 days, but if I don’t want to wait until nearly the first frost to get tomatoes, I need to start them inside now, or start in a greenhouse soon. Some eggplants take 120 days, so the same principal applies.
Another thing you need to look at when deciding if you should direct sow or start seeds indoors is the heat- and cold-tolerance of the vegetable. Tomatoes aren’t tolerant of cold at all, so they can’t be put out until the soil is sufficiently warm (55-60 degrees), and no frosts are expected. To illustrate, if I didn’t start my tomato seeds indoors, I wouldn’t be able to plant until May 9th.
Then we have cauliflower and broccoli. They are both a cooler-season crop, and they don’t produce after late June here in my high desert garden due to the heat. Since they both need almost 100 days to grow and get a harvest, they need to be started very early. Here in Zone 7, I need to start broccoli and cauliflower from seed indoors in February or March.
When is direct sow a better option?
Root crops like carrots, beets, turnips, and radishes are best direct sown. Transplanting these may cause misshapen, stunted roots. And since the roots are the part of these vegetables that you eat, you don’t want them stunted or misshapen.
Fast-growing, cool-season vegetables like spinach and lettuce are also best direct sown. Since they grow so fast, and are quite cold-tolerant, it’s not worth it to start them as seeds indoors.
Choose your pots to start seeds indoors
You need smaller pots, or trays with multiple cells to start seeds indoors. These can be bought at any garden store, or you can get creative and use what you have. I’ve used egg cartons as multiple-cell trays for very small plants, but you could also use eggshells or toilet paper rolls. Many commercial growers use the red plastic cups for sowing tomato seeds. Check out this post for lots of ideas for creative and cheap seed starting pots.
Fashioning your own seed starting pots gives the advantage of using different size pots. This is important to think about, as some plants will get a larger root ball than others when they are ready to be transplanted.
Whatever seed starting pots you use have to have plenty of drainage. Cardboard egg cartons are naturally porous, so you shouldn’t have to do anything. But if you use plastic cups, make sure you put a few small holes in the bottom. A coffee filter over the bottom will keep the soil from falling out of the holes.
Choose your growing medium
When you start seeds indoors, you need to use a high-quality potting soil. Seedling mixes need to be lightweight but still retain water. Most have vermiculite or perlite in them to keep them fluffy, and peat moss or coconut coir for holding water. You can also just buy the compressed coconut coir pellets.
You should choose organic potting soil if possible, but even if you get conventional, it shouldn’t have fertilizer in it. New seedlings don’t need fertilizer until they have 1-2 sets of leaves.
The growing medium should be free of mold or fungus. Don’t re-use your growing medium! And never use dirt from your yard or garden. It can have pathogens that can harm your delicate seedlings.
Sow seeds at the correct depth
Some seeds need to be sown deeper than others. Make sure you read the seed packet directions when choosing how deep to sow your seeds. As a general rule, smaller seeds will need to be buried much more shallow than larger seeds. I usually try for a depth roughly equal to the size of the seed.
For example, Lettuce and spinach seeds need just a very light covering over them. Watermelon seeds, on the other hand, need to be buried about a half inch. Let the seed size and the seed packet guide you through this process.
Decide where you’ll start seeds indoors
After you sow your seeds, you want to keep them in a warm spot, but not necessarily in direct sunlight. I like to place mine in a window sill that gets mottled morning sun. If the area isn’t warm enough, you will want to get a heat mat. The soil in the pots generally needs to be nearly 70-80 degrees for proper germination. You can also set your seed pots on top of the refrigerator.
Germinating seeds need to be kept very moist. Make sure you check them daily and water as needed. Misting the pots almost daily with a spray bottle is the best way to keep them damp, but not too wet.
It’s also a good idea to cover your seed pots with a clear lid, mini greenhouse dome, or clear plastic wrap while they are germinating. This will help ensure your growing medium doesn’t dry out.
Caring for your seedlings
Once your seeds have sprouted into seedlings, and have 1-2 sets of leaves, you will want to put them into more direct light. If your windows don’t have enough light, you might want to buy some grow lights. If you have had a clear cover over your pots, you’ll want to remove that now.
At this point, your seedlings will benefit from weekly fertilizing. Dilute your fertilizer to 1/2 of what the directions say for mature plants.
When your seedlings have 2 sets of true leaves, you also need to thin your seedlings, if you have more than one plant growing from each pot. Tomatoes may also need to be transplanted into a bigger pot at this point, unless you used a larger pot (like a plastic cup).
To help your seedlings get big and strong, it’s a good idea to put a fan nearby that will gently move the plants. Another option is just to lightly run your hand back and forth across the top of them a few times daily.
Harden off your seedlings
Hardening off is the process of acclimating your seedlings to the conditions they will be facing out in the cruel world. Up until now, they have been sheltered from the harsh sun, wind, and temperature fluctuations. So before you leave them to their own devices outside, you need to toughen them up a bit.
A little disclaimer first: if you have recently transplanted your seedlings into bigger pots, you should wait a few days before starting the hardening off process. You don’t want to send them into shock too much!
The hardening off process typically takes about a week, and you will gradually be lengthening the time they are outside. It will be easiest for you if you have all your seed pots on a tray at this point.
Here is the step-by-step hardening off process:
- During the warmest part of the day, when it’s not windy, set your seedlings out in partial shade for 2 hours.
- The next day, put them in slightly more sun, and leave them for 3 hours.
- On the 3rd day, put them in full sun for 4 hours.
- Then on the next day, full sun for 5-6 hours.
- On the 5th day, set them outside in full sun all day long.
- On day 6, you can leave them outside all day and all night, as long as the nighttime temps are going to be well above freezing.
- The last day of hardening, day 7, you can transplant them in the garden!
Enjoy your new garden
Now that your seeds have become beautiful, healthy plants, you get to enjoy your new garden! Starting your garden from seeds is the best way to save money and have a more efficient garden. Don’t rely on those leggy seedlings from the store – grow your own!
Need seeds? Mary’s Heirloom Seeds has over 700 varieties of open-pollinated, heirloom, non-GMO seeds. And with great prices and amazing customer service, you really can’t go wrong!