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When and How to Start Seeds Indoors: A Complete Guide

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Have you been wondering when you should start your seeds?  Or exactly how you should go about it?  If you answered yes, you’re in luck!  This post is dedicated to telling you exactly when and how to start your seeds indoors so you can have the garden of your dreams.

Table of Contents

Why You Should Start Your Seeds Indoors

There are a lot of benefits to starting your seeds indoors, rather than directly planting them in your garden.

  • Starting your seeds indoors gives you a head start on the growing season.
  • If you live in a cooler northern climate, it allows you to grow warm season crops that normally wouldn’t have enough time to mature.  In warmer climates, it can give you time to get a whole second harvest in.
  • Starting your own seeds indoors can save you money – you won’t have to buy expensive transplants from your local nursery.
  • Buying and starting your own seeds opens up a whole new world of possibilities for plant varieties.
  • You’ll know how your plants have been raised – organically rather than bathed in chemicals.

When to Start Seeds Indoors

As a general rule of thumb, you’ll want to start your seeds six weeks prior to your last frost date.  If it’s a cold spring, you may want to delay a little so your soil has enough time to get up to a proper temperature for transplanting.

Starting your seeds will also depend on how long it will take your plant to mature.  The easiest way to figure this out is to read your seed packet.  Typically it will tell you something along the lines of “Start indoors 8-10 weeks before the last expected frost date in your area”.  You can look up your last frost date using the Almanac’s First and Last Frost Dates tool.  Then just count backwards to figure out when you should start your seeds.

What Seeds Should Be Started Indoors?

Not ALL of your seeds should be started indoors.  Some vegetables prefer not to be transplanted, and depending upon where you live, it might be easier and better to directly sow them into your garden.  

We’ve provided a table below that will give you a guideline to what crops are typically started indoors and which are directly sown into your garden.  But remember that this is not a hard and fast rule.  At the end of the day, you should consider what you are growing and where you are growing it.  And remember that experimentation will ultimately tell you what works best for your garden.

Plant
Start Indoors (Prior to Frost Free Date)
Start Outdoors (Direct Sow)

Artichoke

8 to 10 weeks

Arugula

X

Beets

X

Broccoli

4 to 6 weeks

Brussels Sprouts

4 to 6 weeks

Cabbage

4 to 6 weeks

Carrots

X

Cauliflower

4 to 6 weeks

Celery

10 to 12 weeks

Collards

4 to 6 weeks

Corn

X

Cucumbers

3 to 4 weeks

Eggplant

8 to 10 weeks

Green Beans

X

Kale

X

Leeks

8 to 10 weeks

Lettuce

4 to 5 weeks

Onions

X

Parnips

X

Peas

X

Peppers

8 weeks

Potatoes

X

Pumpkins

X

Radishes

X

Spinach

X

Squash (Summer & Winter)

X

Sweet Potatoes

X

Swiss Chard

X

Tomatoes

6 to 8 weeks

Turnips

X

Watermelon

X

What Really Matters: Soil Temperature

While it is easiest to start your seeds indoors by counting backwards from the last predicted frost date, what this is all really based on is soil temperatures, because that is what matters to your plants.

If your soil temperature is too cold, even after the last predicted frost date, transplanting your plants could end up killing them.

So if you want to get down to the nitty gritty and be really accurate on when to transplant your seedlings outdoors, or when you should direct sow your seeds, head on over to your local garden center and pick up a soil thermometer.

Best Soil Temperature for Starting Seeds

Chart for determining the best soil temperatures to start seeds.

How to Start Seeds Indoors

To start your seeds indoors, all you really need is seed starting mix, containers, and a strong light source.

1. Choosing a Starting Mix

There are many different opinions on what kind of soil mix you should use to start your seeds.  The best and most basic mix you can start off with is a seed starting mix.  As you gain more experience in your garden, you can start experimenting to see what works best in your garden.

The only thing you should NEVER do is use soil from your garden to start your seeds.  Your garden soil could contain pests or diseases that would thrive in the indoor growing environment you’ll provide.

It’s also recommended that when you add water to your starting mix to initially hydrate the mix before potting, you use boiling water.  Starting mix can sometimes contain fungus gnats, and using boiling water will kill these eggs before they hatch, avoiding a potentially very annoying problem.

2. Choosing a Container

It really doesn’t matter what kind of container you use, provided it gives you seedling enough room to grow.  I don’t actually use a typical container for starting my seeds, I prefer to use soil blockers that I then put on trays.  If you’re interested in learning more about this technique, I highly recommend that you read the book Nourishing Homestead.  In it, the author outlines in detail how he starts his seeds using this method.

You could also use the standard seed starting trays, or you could use recycled containers such as yogurt cups, plastic muffin trays, or even eggshells.

3. Sowing Your Seeds

Once you’ve chosen your starting mix and your containers, it’s time to sow your seeds!  Make sure that you have adequately hydrated your mix beforehand (preferably with boiling water that you then let cool).

Fill your containers with soil, tamp it down slightly to settle it, then sow your seed to the depth indicated on your seed packet.  If you want to get technical, there are tools that will allow you to sow to the exact depth indicated, but that’s not really necessary.  Seeds want to grow, so as long as you have them approximately where they want to be, they’ll grow.

Also make sure to read your seed packet to see if your seed needs any special attention when sowing, such as scratching the outside of the seed beforehand.

And don’t forget to label!  Use something waterproof (I learned this one the hard way, when the first year I used popsicle sticks labeled with marker.  The first time I spritzed my seedlings with a water bottle, all of my writing disappeared and I had absolutely no idea what was what).

Water your pots carefully, preferably from the bottom if you have your containers resting in a tray.  Place them under your light source, and you’re good to go!

Conclusion

And that is everything you need to know to start your seeds indoors!  Well, maybe not everything, but at least it’s a good primer to get you started.  There are a million and one amazing gardening books out there, don’t be afraid to go pick one up and start expanding your gardening knowledge.  You’ve got this.

Are you looking for some ideas on how to organize your seed packets or seeds you’ve saved?  Check out our post: How to Organize Your Seeds

Do you want to start a garden, but you live in an apartment or a small space?  Check out our post: Unleashing Your Inner Farmer in Limited Space

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I’m a mom to two kids, and I am super passionate about sustainable, clean living.  My husband and I are building our dream self-sustaining homestead, while homeschooling our kiddos.  Have a look around my site for ideas for your homeschool or homestead, or find some new delicious homestead-friendly recipes.  You can also check out my About Me page to learn more about me and my website.

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