Starting Seeds Indoors – Your Ultimate How-To Guide

If you’re getting ready for spring and the garden, you’ve most likely ordered some seeds or picked some up from the local garden or home improvement store.  In a previous post I talked about garden planning and the pros and cons of seeds versus live plants.  Assuming you went the seed route for at least some of your garden like I did, now what?  Depending on the types of plants you want to grow, you will either be starting seeds indoors or waiting until it gets warmer to plant outdoors.

If you’re getting ready for spring and the garden, you’ve most likely ordered some seeds or picked some up from the local garden or home improvement store.  In a previous post I talked about garden planning and the pros and cons of seeds versus live plants.  Assuming you went the seed route for at least some of your garden like I did, now what?  Depending on the types of plants you want to grow, you will either be starting seeds indoors or waiting until it gets warmer to plant outdoors.

Starting Seeds Indoors - The Ultimate Guide






What should You Plant Indoors vs Outdoors

Your seed packet is usually pretty helpful in determining if the seeds need to be started inside or can wait until it gets warmer outside.  Tomatoes and peppers, for example, prefer warm weather, but also need extra time to grow, so they’re generally started indoors.  Carrots and lettuce are a bit hardier (i.e. don’t mind cooler temperatures), so they will wait until it gets a bit nicer and get planted directly outside.

Another factor in determining who gets planted where is the Last Frost Date.  Plants are generally not a fan of freezing cold temps (though there are a few exceptions), so this date let’s you know when there is a good chance of avoiding frost/freezing temps.  It also helps determine how long your outdoor growing season is (i.e. shorter season = more seeds planted indoors, longer season = more seeds planted outdoors).  I am located in Brooklyn, NY, so my last frost date is around April 17th.  To find the last frost date for your location you can google ‘Last Frost Date‘.  There are numerous resources by zip code, city, or zone and I find that all are good options.

When Should You Start Planting Indoors

Once you’ve figured out where the seeds will be planted, label the seed packet with an I (inside) or O (outside).

Labeling seed packets for indoor or outdoor planting
Labeling Seed Packets For Indoor Or Outdoor Planting

As you can see, I have a lot of veggie, herb, and flower seeds, so labeling quickly helps me see what I need to look at now and what I can set aside until after the last frost date.  After the packets have been labeled, move the Os to someplace dry to wait out the next few months when you can start them outside.  Whew!  And the pile gets smaller!  Now, take a look at a calendar and the seed packets you have left.  Each packet will generally tell you when to start planting (ex. 6-8 weeks or 3-4 weeks).  This is the number of weeks before that last frost date you looked up earlier.  I tend to start plants earlier, so the 8 or 4 weeks in the example, but you can plant them anytime in that range.

What Supplies You’ll Need For Starting Seeds Indoors

Now that you know what you’ll plant indoors and when, it’s time to get the supplies needed.  If you have a very sunny window with lots of light throughout the entire day, you can start your seeds indoors without grow lights.  If you’re like me and don’t have a sunny window you’ll need to create your own light source (grow light) for the seeds.  We’ll get back to that in a bit.  First, lets chat about what everyone who grows seeds needs.

Seed Starting Supplies
Seed Starting Supplies


  • Seed Starting Mix – There are a number of seed starting mixes out there, from the loose soil in bags (like the one pictured above) to compact pellets that expand when given water.  After years of working with both I can say that the Best Seed Starting Mix I’ve found starts as loose soil.   Seeds generally want soil that’s light and not compact.  With the loose soil, you can better control how dense each pot is.  I have also found that some of the pellets never fully expand, even after adding water and trying to break up (which is really annoying).  This leads to water getting trapped in the soil and never drying out (a.k.a. mold and dead plants).
  • Seed Starting Trays – For seed trays/pots, I prefer ones like you see above from Home Depot or these ones from Amazon.  They are:
    • Inexpensive
    • Include a tray (to hold water) and clear cover (for when seeds are germinating)
    • Contain separate cells/pots for many types of plants to grow
    • Recyclable (At least the plastic, for when you are finished with the seed starting)
    • Less likely to get moldy like the peat pots can
  • Planting Trays – I am also a BIG fan of the plastic planting trays from Gardener’s Supply!  I provide more details in my favorite gardening tools post, but basically, these trays are super durable, last forever, and catch any spills when watering the temporary seed trays or any pots with holes for drainage.  This is especially useful if you have small hands that like to help water!!

How To Plant The Seeds

1. Once you’ve gotten your supplies and are ready to start planting, add the seed starting mix to the pots/trays.  I find it easy and quick to dump a pile on the tray and then smooth across with your hand. It also keeps the soil from getting too compacted.

Adding seed starting mix to planting tray
Adding Seed Starting Mix To The Planting Tray

2. When all of the cells are filled with soil, you should figure out what will be planted where.  This is especially important if you have seeds that need to be planted later and will need space held for them.

3. I learned this nifty trick to help me remember to hold space (and actually plant the seeds later).  With my basket shears (another favorite garden tool), I cut a popsicle stick in half and write the plant and date to plant on it.

Labeling the seed markers
Labeling The Seed Markers

4. Create as many as you need for placeholders and stick in the appropriate cells.  Be SURE to use permanent ink as I’ve forgotten in the past and could barely read my writing!

Adding placeholder markers to planting tray
Adding Placeholder Markers To The Planting Tray

5. If you have an extra popsicle stick, you can measure and mark a depth line for how deep to plant the seeds.  This comes in handy when planting a lot of seeds.  To find out how deep you should plant your seeds, follow the instructions on the seed packet.

6. So, how many seeds should be planted in each cell?  This really depends on how many plants you want to grow and how many seeds you have.  I try to grow 1 plant per cell and, knowing that not all seeds survive, I usually add 4-5 seeds.  For large seeds, like squash, beans or peas, I only put 2 in a cell.  Occasionally, like my geraniums last year and my petunias this year, you’ll receive a very limited amount of seeds, like 10.  In this case, I usually put 1 seed per cell and cross my fingers!!

7. Once all of the seeds are planted, its time to water!  Be sure to give everything a good soaking as it helps with germination.

TIP:  The first time you water the seed starting mix, the water may just sit on top.  To get it to sink in and not disturb the seeds, poke the soil with a toothpick or needle.

Soaking Overnight

There are some seeds that require soaking overnight to help the seeds soften and germinate.  An easy way to do this is to soak a paper towel in water and squeeze out the excess.  Lay the paper towel flat and spread the seeds out on it.  Cover with another wet paper towel and lay it on top of the tray (with the clear plastic lid on) overnight.  Plant as usual.

How to Make Your Own Grow Lights

There are many beautiful, but pricey, grow lights on the market.  If you have a budget for some, I’d take a peek at Gardener’s Supply.  There are a number of options that are on my wish list!  If your budget is tighter, like mine, I’ve found an economical way to make my own grow lights.  Definitely not as pretty, but they get the job done.

  • Fluorescent Lights (I bought ones like these at Home Depot)
  • Bookcase (or anything you can hang the lights from)
  • Wire, Twine, Ribbon or Chain for securing lights

I have made many iterations of these grow lights over the years, hanging them in a large fish tank or on our mantle.  After years of temp solutions, I finally bought a metal bookcase from Ikea last year and it has been my grow lights area ever since.  Once you’ve figured out where to hang the lights from, you’ll need to actually hang them.  I have a ton of wire at home, so I wrapped it around both ends of the light making it easy to hang.  Ribbon or twine will also work as the fluorescent lights do not get that hot.

The last and really critical piece about grow lights is the ability to raise and lower as the plants grow.  Using ribbon, I can easily untie and re-tie whenever I need to by just tying a bow (like tying your shoes).  For whatever you choose (ribbon, twine, chain, etc), just don’t tie anything permanent that you cannot undo and adjust!

Hanging adjustable lights for seedlings
Hanging Adjustable Lights For Seedlings


  • If you need to setup grow lights, I would suggest getting figuring that out before you start planting seeds.  This way the plants will have light the moment they are ready (rather than racing to get it done).
  • Once the seeds are planted, move them to their final destination before watering (as they will become heavy very quickly and can turn into a watery/muddy mess in transit).
  • After watering the seeds for the first time, place the clear plastic lid on top.  This will hold moisture in while the seeds start to germinate.
  • Hang the lights low, so they are just above the lid.  This will prevent the plants from bolting, reaching towards the light and not filling out properly.
  • Add more water to the tray when the water level gets low, but not dried up.  The goal is to keep the soil moist, but not too wet or dry.  If you check everyday or so, you’ll figure out what works for your home.


When To Tilt/Remove The Lid

Once you planted your seeds, added water, and placed the clear lid on top, you’ve created this warm humid greenhouse that’s great for most seeds to germinate (become cute little seedlings).  The telltale sign that there’s enough humidity is that water droplets will form on the inside of the clear lid.

Once seedlings start to pop up, however, they will want some fresh air.  The circulation will also reduce the chance of unwanted mold or fungus growth.  If only some of your seedlings have appeared, tilt or angle the lid to start allowing air in.  When most of your seedlings have appeared, remove the cover all together, so everyone can get some fresh air.

Humidity inside seedling planter
Humidity Inside The Seedling Planter

How Much And Often To Water

As was mentioned earlier, ideally the soil should be moist, but not too wet or dry.  Check the soil everyday to see if any water needs to be added.  In the case of one of my trays last year, I actually over watered and there was a lot of water lingering in the bottom of the tray for longer than I’d like.  If this happens, you’ll need to pour that excess water out like I did.  Either carefully remove the group of cells and empty the tray OR bring a bucket close by and tilt the tray (with the plant cells still inside) gently.  I strongly recommend getting a second set of hands to help if you are going with option two.

Remember To Finish Planting The Rest Of The Seeds

If not all of your seeds were planted at the same time, like my tomatoes and squash, be sure to remember to plant those as well.  If you wrote the dates on your markers, then it makes remembering even easier.  Since these late starters will want that warm humid climate too for germination (and you may have already removed the lid), you can place some plastic wrap on top of those cells.  Once the seedlings start to pop up, just make sure you remove it.

When To Swap Out Or Remove The Markers

This tip is really a personal preference.  Ever since I put in placeholder markers (those popsicle sticks we chatted about in the last post), they’ve been soaking up moisture.  This is especially true when they were sitting under that warm, moist greenhouse (a.k.a. lid) that we created.  By the time you and I are ready to actually plant in those cells, the markers are quite soggy and a good place for mold/fungus to begin growing.  To avoid that, I either remove them all together, or in the case of my tomatoes, since I have 4 varieties to tell apart, I swap them out for new dry markers that I can label with each type.

Seedling Markers
Seedling Markers

How To Thin Out Seedlings

If you are fortunate enough to have multiple seedlings in one cell, you will eventually want to remove all but one seedling.  This will allow enough space for the seedling’s roots and light for its leaves.  There are a few exceptions, however, such as onions which grow straight up and can handle multiple seedlings in a crowded space.


  • Wait until the seedlings are at least 3/4″ – 1″ tall.  You want to pick a strong seedling to keep, so it will be easier to see once they grow a bit.
  • If you have several strong seedlings to pick from, keep one that’s close to the center of the cell.  This will allow it the most amount of growing space in the cell.
  • Use a toothpick, needle, or something else small and thin to hold the seedling at the base, so you pull out only that seedling and as little soil as possible.
Thinning out seedlings
Thinning Out The Seedlings

    Can I Move Seedlings To Vacant Cells?

    There is generally a cell or two that didn’t have any luck in growing seedlings.  And that’s ok!  As part of the thinning process, you can take one of those strong seedlings that didn’t make the cut and give it a new home in that vacant cell.  Be sure to dig a big enough hole for the roots with that toothpick/needle.  Also, ease the soil back to just cover the roots, so it doesn’t get too compacted.

    When To Raise The Lights

    The last tip for continuing on this seed starting journey is about your lighting.  Be sure to raise the lights as the plants grow.  Ideally, about an 1″ above the plants, so nothing is touching the lights and they aren’t reaching towards the light because it’s so far away.

    I hope these tips and tricks help your seedlings continue to thrive as we creep closer and closer to spring and that beautiful garden!

    What are you growing indoors?  I’d love to hear about it in the comments!

    Until next time…happy gardening!    Nikole

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