Start Seeds Indoors: A Step-By-Step How To

Why Start Seeds Indoors?

Let’s start off with the “why” in case you’re not convinced it’s worth the effort to start your vegetable garden from seed. For me, there are two main reasons I like to grow my garden from seed: Price & Diversity.

Reduce your garden costs by growing from seed

Let’s start with price. Most seed packets cost $2-$3, maybe up to $5 if you are buying an heirloom organic variety. And for many plants, each packet comes with dozens (sometimes hundreds) of seeds. Sure, you may not need that many. But you probably will only need one seed packet per variety you are planting. Compare that with purchasing ready-to-transplant starts from your local nursery. BEST case scenario, you may pay $2-$3 PER plant. In most cases probably more than that. I’m guessing you want more than one head of lettuce, one kale plant, and one pepper plant in your garden. So I think you can see where I am going with this…

Another tip is that in my experience, seeds will also last for quite a few years. I know it’s recommended to buy new seeds each year. However, I usually just keep using the ones I have for the varieties I love. If the seeds are getting on in years I will plant a few extras to germinate in case they are loosing their life. Thus far I’ve had good success continuing to use my seeds until they are used up, even if it takes a couple years. This way, once you’ve invested in your “core” vegetables, you only end up purchasing a few packets of seeds every year. This keeps your “startup garden” costs quite low each season.

Increase your vegetable diversity if you grow from seed

What about diversity? For me this is the most enjoyable reason I choose to grow from seed. The ability to try lots of new varieties of vegetables that I will never see in the grocery store or my local nursery has become one of my favorite parts of growing our own garden. Every season I try to explore a new variety or two. When we find one we love, I add it to our “faithful favorites” to be planted again the following year.

So hopefully if you were on the fence, now you are convinced that it is totally worth it to grow your garden from seed! If you’re with me on that, then the ability to start seeds indoors can be a game changer. Not only will you save money and increase your garden diversity. You can also extend your garden growing season by several months in most cases. And who doesn’t want garden-fresh produce for longer?!

Start seeds indoors if you have cold winters

You may think you only need to start seeds indoors if you live in a climate where you have cold winters. This is definitely one scenario. In this case, you can start seeds while the ground is still cold and frozen. As soon as it begins to warm up, you have transplants ready to go! If you’ve timed it right, you have probably added at least 2 months to your growing season by starting seeds early.

However, you can also use this method to extend your growing season if you live in a hot climate!

Start seeds indoors if you have hot summers

I live in the Phoenix Arizona area, and temps never drop low enough in winter for the ground to freeze. Sure, we have lots of sun and warm weather. But that means that we actually end up with a short spring growing season. It is shortened by the summer temps rising too high for plants to produce well. (Or survive at all, depending on the variety.) Getting a jump start by starting seedlings early helps me extend my spring growing season here as well! The winters and early spring are cold, and not ideal for germinating seeds directly in the ground. But once seedlings are started, there are many varieties that will grow really well in the cool weather. Early spring is the BEST time of year for lettuce, kale, chard, collards, radishes, broccoli, peas… The list goes on!

I also start seeds indoors to get an early start on our second fall growing season. When the temps “drop” to about 100F, that is the time to get started with new fall seed starts. If I were to direct sow new seeds outside, they would whither and fade away due to the still-hot temps. Instead, if I start these seeds indoors, by the time the temps drop to good growing weather (70s and 80s), I have well established seedlings to transplant. Leveraging this jump start, I can get productive growth from these plants for months! Often even well into spring for crops like lettuce, kale, chard, broccoli, etc.

What do you need to start seeds indoors?

So now the big question – where to begin? I’ve listed the essentials that you’ll need below, and I’ll go into a little further depth on each one.

• Seed starting and growing station – take a look at my full article on how to make your own
• Planting trays
• Dirt
• Seeds

Planting Trays

I use two main sizes of planting trays to start seeds indoors:

1. Small 6-cell seedling starter trays for initial germination. You can even use cardboard egg cartons for this step! This link is to a tray I have purchased on Amazon. I have been re-using them for several seasons, and they are holding up well.
2. Larger 3.5″ square pots. The exact 3.5″ pots I have are no longer available. However, there is a similar pot by the same brand available on Amazon now – these McConkey 2.75 inch square pots. Or keep any similar sized pots from the nursery to repurpose. You can even use empty (and cleaned!) quart-sized yogurt cartons!
3. Sometimes I will also use one size larger from the 3.5″ pots, if I’m not ready to put the seedlings into the garden for some reason. In this case I’ll often just use a larger pot I’ve saved from the nursery. (I save most nursery pots!) But you could purchase one size larger to have on hand as well if needed.

In addition to the pots themselves, you will need some larger trays to hold all your little pots. The classic 1020 seed starting trays work well. They make it easy to move the seedlings around to rearrange, water, harden off outside, etc. Be sure to pick a sturdy brand without holes for this part of your setup. There are lots of options to choose from for these trays. Just do a quick search on Amazon for 1020 trays, or take a trip to your local nursery!

You will also want a couple of trays that have a humidity dome. You can get your 1020 trays with domes, or choose a different size base tray with dome that can fit a number of your 6-cell trays. The trays I have are no longer available, but again these aren’t hard to find if you look around. You will use these at the outset of your germination phase to keep the soil moist and humid for germination.

Optional: Heating Pad

Lastly, depending on the seeds you are starting, you may want a heating pad. I have found that eggplant seeds almost require sitting on a heating pad to germinate. Chiles and peppers also seem to do better if you put them on a heating pad for a few days. For this, I just set the pad under the large tray where my 6-cell starts are housed. I put it on the lowest setting, and leave it on continually until the seeds sprout!

Dirt

You will need two types of dirt to start seeds indoors. First, a seed starting mix for when you first plant your seeds. I’ve tried a few varieties, and really like this Black Gold seedling mix I found on Amazon. But there are lots of varieties that will work! Just choose something that is specifically for starting seeds. These mixes will be sterile, light, and very good at retaining moisture. This is important for those first days of your seedling’s life!

The second type of dirt you’ll need is just a basic raised bed mix. You will use this when you transplant your seedlings up to a larger pot. I like something that has a compost component to it (E.B. Stone is a favorite brand that our local nursery carries). This will give your seedlings more nutrition while they continue to grow indoors.

Seeds

Most importantly are the actual seeds!!! I have a few places I have bought seeds, and have been pleased with all of them. I’d suggest you browse around to these and other sites to find vegetable varieties that you would like to try! Also check out your local nursery, and see if they have varieties you’re interested in. A word from the wise here – don’t wait until the last minute to order your seeds! I’ve found that often the seed varieties that are popular for a certain season can be difficult to find if it is right at planting time. Instead, I try to plan my garden ahead by a few months. This way I can order early to be sure to find everything I want.

Below I share the main sites that I purchase my seeds from. I like these online stores as a supplement to my local nurseries. They have a lot of heirloom varieties and other unusual options that I don’t usually see locally.

• Terroir Seeds (Underwood Gardens) – local to me here in AZ so I like to support them!
• Baker Creek Heirloom Seeds – this shop has a lot of really unique varieties! I love to browse… and usually have to limit myself to a predetermined quantity! Otherwise I would purchase more seeds than our garden can handle!
• Native Seed SEARCH – another local AZ store who carries only varieties native to our SW desert climate
• Johnny’s Selected Seeds – this shop has a really vast, comprehensive catalogue

The Timing: When to Start Seeds Indoors

In order to determine the right timing to start seeds indoors, you need to know the right time to plant transplants out in your garden.

I typically start seeds at least 8 weeks before I want to be able to transplant them in the garden. For most vegetables, you can plant them within a 6-12 week window, so you don’t have to be exact. This also gives you some flexibility to adjust with the weather if needed.

Please check out my other article on specific timelines I’ve come to use for my Arizona garden (zone 9b).

If you live elsewhere, or are growing varieties I don’t mention specifically, there are lots of great resources available. Just google your “city/state” and “planting calendar” or “garden calendar”. You can also check out this link to The Old Farmer’s Almanac as a starting point. I like to compare a couple recommendations just to be sure I have a solid plan.

Plant and Germinate

Planting the seeds is pretty simple! Moisten the seed starting mix with water and stir it up until it is evenly moist. Transfer the dirt to your 6-cell trays. Leave a little room at the top, or make a shallow hole with your finger. Add 2-3 seeds per cell, cover with a little more damp soil, and tamp down. (Note – read the back of each seed packet for recommended planting depth. Most seeds should be planted at 1/4 inch depth, but a few recommend deeper.)

Place the seed starting cells in a 1020 tray (or similar) and cover with a humidity dome. For chiles, peppers, and eggplants, I strongly recommend placing the tray on a heating pad set on low until the seeds have germinated. This will greatly speed up the germination period for these particular seeds.

Also, don’t forget to label your trays! If you are starting multiple varieties, it can be difficult to keep track of which is which, at least until they are bigger. If you’ve made a garden plan, you want to be able to track the varieties. This will ensure you plant them in the right places in the garden when the time comes.

One more tip for planting seeds – I usually start a few extras of each variety. This way, if any of them don’t make it for some reason, I still have plenty to fill my garden. Once you have established starts you don’t necessarily need to keep these extras going, especially if you are tight on space! You can just add them to your compost pile, and they will continue benefiting your garden in that way 🙂

Grow the Seedlings

Once the seeds have germinated, you can remove the humidity dome and turn your grow lights on. You will want the grow lights on for 12-16 hours a day. If not all the seeds in a tray germinate at the same time (and they rarely do!) I will leave the humidity dome on, and turn on the grow lights. This gives the seeds that have sprouted the light they need, but keeps the conditions good for the rest to germinate.

I have so far come across one plant variety that requires light to germinate, although there may be more! Lettuce seeds require light, so you will want to put them under a grow light from the get-go.

Once the seedlings have their first or second set of real leaves, I plant them up from the 6-cell trays to the 3.5″ pots. Once there, I grow them for another 4-8 weeks before transplanting outside. When planting them up, you will use the raised bed mix that has compost in it. This will give the seedlings some initial nutrition, before you start feeding them regularly.

Feed the Seedlings

You will also want to feed the seedlings every 2-3 weeks while they are growing indoors. I feed them for the first time once they have been growing in the larger pots for 2-3 weeks. Keep an eye out for the leaves starting to yellow, as that is a sure sign they are ready for a nutrition boost! I like to use a dilute organic liquid fertilizer like fish fertilizer. (Fish fertilizer is smelly, as you can imagine! I feed them outdoors and let them “air out” in the shade before bringing back inside.)

Transplant the Seedlings

Once the temperatures are right for planting your seedlings, you can get them ready to go outdoors. You’ll want to harden them off for a few days up to a week (depending on how extreme the outdoor temps are). If its still relatively cool, or warm, then I give them longer to acclimate before transplanting them into the garden. If you are planting them into moderate temperatures without low dips at night, you won’t need to harden them off for long. Test it out for a day or two and if they seem unphased, you are good to transplant!

Before transplanting, I usually amend some all purpose fertilizer into the garden bed the week or two before the transplants will go in. This refreshes the soil and ensures the needed nutrients are present. I will also sprinkle a little of this same fertilizer into the bottom of each new plant hole when I am ready to plant out the seedlings. For an all purpose fertilizer, I like this granular EB Stone Organic All Purpose Plant Food. It has worked really well for us in our garden!

To harden off your seedlings:

1. Ensure they are well watered before taking them outside.
2. Put them outside in the shade for a couple hours a day, for the first couple days.
3. Add some time in the sun, keeping an eye on them in case they get super wilty.
4. Gradually increase the amount of time they are outside.
5. Once the seedlings are doing fine outside for 6-8 hours at a time, they are ready to transplant into your garden!
6. If the nights are still cold (40s or below) consider covering them with a light row cover. This will help them acclimate to the cooler nighttime temps a little better.

Enjoy Your Homegrown Vegetables!

To grow a healthy garden throughout the season, keep it consistently watered, and fertilize at least once a month. I like to use that same organic fish fertilizer at standard strength to give the plants a regular boost. We also feed the fruiting vegetables like tomatoes, eggplants, and chiles every 6 weeks or so. For them, we use an appropriate granular fertilizer mixed in around the base of each plan to ensure a productive harvest. This EB Stone Organic Tomato and Vegetable Food has worked really well for us.

Since our summer temperatures can get quite warm, we also like to mulch the top of our garden beds. We use a couple inches of straw to help keep the soil cool and consistently moist. We’ve used “EZ-Straw” as our mulch and it has done the job well.

Lastly, this may seem silly to point out, but don’t forget to regularly harvest and enjoy the vegetables you have put all this work into growing! For most varieties, the more you pick the more they grow. So, once they start producing a little extra, don’t be shy to pick and prune. They will keep growing and give you more!

Need some ideas for how to build raised garden beds?
Read my article on how we built ours here!

Resources mentioned in this article

seedling starter trays

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McConkey 2.75 inch square pots

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Black Gold seedling mix

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EB Stone Organic All Purpose Plant Food

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EB Stone Organic Tomato and Vegetable Food

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EZ-Straw

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