6 Mistakes to Avoid When Starting Seeds Indoors • Gardenary (2024)

Indoor Seed Starting Is an Opportunity to Make Lots of Mistakes

If you've ever attempted to start plants for your kitchen garden by seed indoors and ended up with trays that grew only mold or seedlings that died the minute they were placed outside, you know that it can be really difficult to get it right. We have to recreate nature inside our homes, after all, and time everything to near perfection.

And if you've never attempted to start seeds indoors, then just know that it's more of an advanced gardener skill and you're wise to do some reading up on it before you begin.

It’s taken me years to develop my techniques to recreate nature inside, and even still, something goes wrong every season.

The best way to ensure success, at least in my experience, is to avoid committing one of these six mistakes.

Seed Starting Mistakes:

• Putting your seed trays in a windowsill instead of under grow lights
• Watering from the top
• Not setting a schedule and reminders
• Not thinning your seedlings
• Fertilizing your seedlings
• Waiting too long to pot your seedlings up

Keep reading to find out how you can avoid these mistakes and increase your chances of producing happy and healthy little seedlings for your garden.

Putting Your Seed Trays in a Windowsill Instead of Under Grow Lights

When I first got started, I was convinced my seedlings would be perfectly happy growing in a south-facing windowsill.Why invest in artificial grow lights, I reasoned, when I can use free solar light?

It took me a couple of seasons of seed starting and lots of experimentation to come to the conclusion that you can keep seedlings alive in a south-facing window. But you don't just want your seedlings to germinate and then stay alive. You want them to rapidly grow into strong, healthy plants that will thrive in your garden space.

And the best way to make that happen is starting seeds indoors with grow lights. Seedlings grown without artificial light tend to be leggy (or tall and narrow without many leaves) or lean over too much because they're looking for sunlight. They might also just grow very slowly. It's rare for baby plants to get enough light to be fully healthy and robust from just sunlight indoors.Seedlings like their light source very close to them, so give them what they want and grab one of these artificial light sources.

Overall, you'll find better and more consistent success with an artificial source of light.

Watering Your Seed Trays from the Top

A couple years ago, I noticed my social media feeds were full of houseplant influencers filling their sinks with water and setting their potted plants inside like they were giving them a bath. I've found it's best to apply a similar technique to your seedlings.

Watering your seed trays from the top risks disturbing or even displacing the tiny seeds you've just planted. Unless you're very careful, you can also more easily over- or underwater your trays. Bottom watering does not disturb the newly sown seeds or fragile seedlings, and the seed starting mix will only absorb as much water as it needs.

To bottom water, you'll need a non-draining tray to hold the water and then a draining tray, or a tray with holes in the bottom, that contains your seeds. (Learn more about different seed starting tray options.)

You'll fill the bottom of the non-draining tray with water and then set the draining tray inside. You don’t need to add a lot of water because your seed starting mix should still be damp from when you rehydrated it before planting your seeds. Lock in moisture by covering your trays with a dome, a piece of burlap, or a dishcloth until your seeds germinate.

Check the moisture level in your seed trays every day and add more water to the bottom tray as needed.

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Not Setting a Schedule and Reminders for Yourself

Taking care of your seedlings each day is a quick but essential part of your routine. If you're not in the habit of turning on the grow light each morning when you wake up and turning it off at night before you go to bed, set yourself simple phone reminders or alarms.

Alternatively, you could look for lights with built-in timers or remotes to simplify your life (these features are pretty standard in lights now). All you have to do is set your timer to click on every morning and off every evening. Even with the convenience of automation, make sure to check on your seedlings twice a day to make sure the timer is working and the seedlings look healthy.

Not Thinning Your Seeds

Some seeds are so small that they’re hard to separate out, let alone see where they've dropped on the soil. Even though I remind myself "a stitch in time saves nine” as I'm holding tiny oregano seeds in the palm of my hand, I often end up just sprinkling seeds over the seed starting mix, knowing I'll have to come back and thin later.

If you end up with two or three seeds trying to grow in one cell, that forces young seedlings to compete for resources.You'll need to thin your seedlings (basically, pluck all but the strongest-looking one) when multiple seedlings have germinated in the same cell.

Some gardeners just can't stand pulling something that's already growing, and if that's you, then try your best to place just one seed in each cell. Of course, by planting this way, there is now a higher chance that some of your cells won’t produce plants. You can always sow a new seed in that cell and try again if that's the case.

Adding Too Much Fertilizer to Your Seedlings

Seed starting mix is light and fluffy, which is ideal for tender plants that need an airy space to push roots into, and it’s also largely empty of nutrients. Because of that, I often see people adding things to their mix to deliver more nutrients to their seedlings.

Here's the thing: Each seed contains enough food to feed itself during its initial growth. You could compare the stored nutrients inside a seed to the placenta that serves as a feeding channel for a baby mammal growing in the womb. (I've said it a thousand times before, but I'll say it again: Seeds are pretty incredible.)

That simple bag of organic seed starting mix you buy from the store is the perfect medium for your seedlings to grow in. To add fertilizer is to risk overfeeding your seedlings. A couple of years ago, I added a fish-based fertilizer to a tray of healthy shoots, thinking I was doing the right thing. I ended up burning all of my seedlings. Burning basically means overstimulating or giving too much of certain kinds of nutrients to a plant.

Your plants will only need extra nutrients once they’ve produced their first true leaves. For many of the plants you'll start from seed indoors, this is also the ideal moment to move them to the garden, where they'll encounter lots of nutrients they'll need to adjust to their new home and grow larger.

That means you only need to worry about fertilizing seedlings that need a longer time to grow indoors, such as eggplants, tomatoes, squash, or cabbages. Start a 7-day free trial of our membership program, Gardenary 365, to watch our Seed Starting course and get tips on how to feed seedlings that need more time to grow indoors.

Waiting Too Long to Pot Your Seedlings Up

Your seeds were meant for bigger things than a small cell in a seed starting tray. When I started my first tomato seeds indoors, I kept them in their tiny cells for way too long until I could move them out to the garden, and very few recovered from having their roots so stunted.

There are about as many differing opinions on when you should transplant your seedlings as there are gardeners in the world. Some gardeners believe you should move your seedlings to a larger space as soon as they sprout. Basically, when your plant pops up, it’s time to pot up.I prefer to transplant after the first true leaves appear.

Potting up is especially important for those large and lengthy plants that will spend a long time growing indoors before being moved outside. Think broccoli, brussels sprouts, tomatoes, and eggplants. If these little guys outgrow their containers but still need more time inside before they're ready to be transplanted to the great outdoors, their growth can be halted.

Because these plants need so much space, some gardeners start large and lengthy plants in four-inch pots instead of cells to avoid transplanting them so soon after germination. It might take you a couple of rounds of seed starting to learn your preferences on whether to pot up after the true leaves appear or just start in larger pots.

Get All the Gardening Tools You Need to Grow Your Seedlings in the Garden

As soon as you're ready to move your seedlings outdoors, you'll need a hori hori, an essential planting tool for the kitchen garden, and, of course, labels to mark which seedlings you're planting where. Don't forget pruners to help you harvest from your seedlings in just a couple of weeks!

Find More Indoor Seed Starting Tips and Resources Here at Gardenary

There are so many more mistakes you can make while starting seeds indoors, and you better believe I've probably made them all. The number of things you can do wrong and the number of things that can go wrong are the reason that seed starting indoors is considered an advanced gardening skill.

But you shouldn't let that discourage you. Each failure is a lesson. Do your best to figure out what went wrong, change something up, try a different solution, and try, try again. You’ll continue to learn each gardening season and eventually refine your technique.

Your efforts will be worth it in the end, I promise. Seed starting indoors can offer you so many incredible advantages over the gardener who never makes the effort.

We've got lots more lessons and tips waiting for you in our Seed Starting course inside Gardenary 365. Our goal is to help every gardener have the confidence and skills needed to start their own seeds indoors, so we're constantly releasing more resources.

Thanks for being here and growing with us!