How to Start Seeds Indoors: Everything you need for success!

Starting seeds indoors is a great way to lengthen your growing season and beat the winter blues while you wait for spring. Though not all seeds should be started inside, here are our favorite vegetables that you can start indoors today - along with tips for creating the best transplanting experience for you and your plants.

6 week old tomato seedlings in plastic potting trays

Every year, when the promise of spring starts to peek its head around the wintery corner, I start planning for the next garden. This is the time to gather seeds, prep-potting soil, and get your seedlings started!

Starting Seeds Indoors

As a gardener, there’s no better news that planting season is almost here, but if you haven’t started your seeds inside yet to prepare for spring transplanting, the time is now. After years of experimenting with starting seeds indoors, I’ve learned that there are some that simply transplant much better than others.

In addition, some vegetables are simply better suited to being started indoors, whether that’s because they need a longer growing season or are finicky when they are sowed directly into the ground.

Why Start Seeds Indoors

You may be wondering, what's the point of starting seeds inside? Is it really worth the hassle? And I used to feel the same way! Here are some of the reasons we now choose to start some seeds indoors.

Longer growing season - Even though we have a very long growing season here in 8b, having fresh food for more of the year is important to us.
Saves money on seedlings - Starting your own seedlings means that you don't have to rely on the local stores having what you need. And it saves money too!
Faster produce - Starting seeds gives you a much shorter time to wait for produce, compared to planting the seeds in the ground once the weather is warm enough.
Peace of mind - Know exactly what's in the soil and what type of seeds are being used. There is no guesswork when you start your own seeds!

When to Start Seeds Indoors

The standard line is that seeds need to be started indoors about 6-8 weeks before the last frost in your area. You can use our seed starting guide to learn more about direct sowing and transplanting in your area.

We have started seedlings up to 4 months before our last frost, so that we have very mature plants to go into the garden as soon as the weather was right. We did have to repot them into larger pots twice during that time, but as a result we had produce very quickly after transplanting.

Seedlings in various containers sitting in front of a large window.

What do you need to start seeds indoors?

While starting seeds indoors is a pretty straightforward process, there are a few things that will make it easier and will help your plants thrive before being transplanted.

Containers - This can range from reusable seed trays purchased specifically for seed starting, or even egg cartons or other cardboard pieces turned into DIY seed starters.
Potting mix - You can make your own potting mix, or you can use mushroom compost (that's what we do) so that the soil is the same as the soil it will be going into, without being too hard.
Grow lights or sunlight - Lastly, you need a good source of light for your plants to thrive. If you don't have a windowsill or greenhouse for them to grow in, you can also grab a set of grow lights for your space.

How to start seeds indoors

Like I said, starting seeds inside is a pretty straight-forward process, but here are a few things we've learned to help with germination and growing strong plants.

Follow seed packet depth - Different seeds need to be planted at different depths. So be sure to check the seed packet for the recommendations for the seeds you are using.
Label your seeds - Until you are very familiar with what different sprouts look like (and even then) it's a good idea to label your seedlings! Even different plants in the same family look the same until the fruit begins to appear.
Water in - After you've planted your seeds, place them on a tray or container without holes, then water the plants in well. A good soaking after planting will help with the germination rate, and will help your seeds thrive!
Set in a sunny spot - Finally, your new little seeds need a well lit windowsill, a greenhouse, or a grow lamp to help them grow properly.

Which Seeds are best to start indoors?

Not all seeds should be started as transplants. Some need to be planted directly into the soil, as they do not like to have their roots disturbed. Here are some of our favorite plants that can be successfully started early and transplanted.

And remember - starting seeds is a great way to get your hands in the dirt long before the snow has melted and the ground has thawed outside.

RELATED: DIY Recycled Seed Starters

NOTE: This list is by no means exhaustive, and there are plenty of vegetables you can start from seed indoors to produce a more successful harvest later on. A good rule of thumb is that any vegetables that have a longer growing season or need certain conditions early on (such as tons of heat or perfectly draining soil) are good candidates for indoor sowing.

1. Cruciferous / Brassicas

We’ll lump broccoli, cauliflower, red and green cabbages, and brussels sprouts together here. This is a vegetable family that definitely needs to be started indoors - honestly, no matter where you live.

Cruciferous vegetables takes a long time to get going, and if you wait until after the last frost to seed it, you won’t have much time before it gets hot and your heads start to bolt. These plants needs to be started when it’s still cold outside to see good results, but start it too soon, and it can be snow-killed.

Therefore, windowsill planting is a good idea. Start it inside about eight weeks before your last anticipated date of frost. It likes to be kept cool, so keep the sown seeds in an area where temperatures rise no higher than about seventy degrees. Leave the seeds covered with plastic until they germinate, and then thin your seedlings for maximum growth.

Once your plants are ready to go outside, I recommend planting in the Back to Eden gardening method. This will allow you to have better control over weeds (cruciferous plants hate competition), drainage, and soil composition - factors to which this plant is quite sensitive.

2. Summer Vegetables

Tomatoes, cucumbers, melons, and zucchini are another set of crops that are perfect for starting indoors. While your seed packet might say that the plants mature in sixty or seventy days - that’s not counting the time to fruit. Tomatoes, for example, usually take about sixty-five days….plus an additional six weeks. That’s a long time if you’re dying to get some fresh produce after all long winter!

Instead, start your seeds indoors about six weeks before the last predicted frost. Unlike cruciferous, summer vegetables don’t like to be cold, so you need to make sure your soil is toasty and that temperatures where you sow your seeds don’t drop below 50 degrees. This is why summer vegetables are prime candidates for indoor seed starting!

Use large pots so that you don’t have to transplant from smaller cells later on. I recommend using a heat mat and covering the pots with plastic to ensure good germination rates. You can remove the plastic once the seedlings emerge and thin once the plants have leaves. And remember, always harden off your plants before moving them outside.

Also check out our full guide on growing tomatoes from seed to harvest!

3. Eggplant

I absolutely love eggplant, but up until a few years ago, I was terrified to make an attempt at growing it. Lucky for me, I’ve got a foolhardy sense of humor and finally gave it a go. I quickly learned that eggplant is much easier to start indoors than to direct sow outside.

You need to sow your seeds at least eight weeks before the plants themselves are ready to be planted - meaning eight to ten weeks before your last expected date of frost, as eggplant likes the heat. I should also note that eggplant seeds should be soaked in warm water for 24 hours before sowing - a task that you will likely have much more time for in February compared to May.

4. Peppers

Peppers are a lot like tomatoes in that they absolutely LOVE the heat. I’ve had a lot of success transplanting pepper seedlings into soil that is warmed with a sheet of heavy black plastic - and that’s after waiting until June to sow!

Starting pepper seeds indoors is a great way to increase the likelihood that these cold-sensitive plants will be successful outdoors. You should start them in a location that is roughly 75 degrees Fahrenheit during the day and receives plenty of sun for best results.

5. Peas

While most people recommend starting peas outdoors, you can start them indoors, transplant carefully, and have great results!

Starting peas indoors lets them get a jump-start on the growing season, benefiting from cool (yet moderated) temperatures indoors, before they need to be planted outside. Once outside, they can get a couple of solid months of growth and production before the summer heat kills them off.

A word of caution, though - when transplanting peas outdoors, you need to be careful not to damage the fragile root ball. This isn’t one to let the kids help you on! Instead, disturb the ball as little as possible and place the seedlings about six inches apart in well-drained soil.

Hardening off

So you have your beautiful seedlings and you can't wait to get them in the ground! But first thing's first. Before you can transplant your seedlings, it's a good idea to harden them off so that they can handle the shock of going from tray to ground.

Here are a few things that you can easily do to harden your seedlings before transplanting:

Only warm weather plants - Fortunately, you don't need to harden ALL your seedlings, instead only summer plants really benefit from the experience. Cold weather plants are fine with hardening.
Mimic wind - To help prepare them for the transfer into an unprotected environment, you can mimic the wind to help them strengthen their stems and roots. Do this by installing a small fan, or by simply running your hands over them in a different direction each day as they grow.
Slow temper the plants - Just like eggs being added slowly to a hot mixture, you need to slowly introduce your seedlings to the outside temperature. Take them outside into a shaded area for an hour or two for the first day, then bring them back inside. Do this in increasing amounts, and with less shade until they can handle the full sun all day/night. Then they are ready to plant!

When to transfer seedlings

Your plants are hardened off and you are ready to get them into the ground! So, let's talk about when and how to transfer them into their outdoor homes.

There are two factors that determine when you can transplant your seedings:

Weather conditions - For warm weather plants, you want to wait until the soil has warmed up to a nice 60-70°F. Whereas for cool weather crops (such as cruciferous) you can transplant them as soon as the soil is at least 50°F and the last frost date has passed.
Age of the seedlings - While cool weather crops can be transplanted as soon as the weather is right, even as young as 3-4 weeks old, warm weather crops are different. For warm weather crops such as tomatoes or squashes, waiting until they are at least 6 weeks old will help them establish better into the new soil.

How to Start Seeds Indoors