Starting Seeds Indoors

Starting seeds indoors under fluorescent lights

Starting seeds indoors is the best way to shorten your time to harvest. You will shave several weeks off the wait for that first juicy tomato if you start your own seeds indoors, and for those with very short growing seasons it may be necessary. Besides, starting our own seeds indoors gives us bored winter gardeners something really fun to do while it's still too cold to go out and get our hands dirty! Below the link boxes are complete instructions.


Seedlings need very bright light to keep from growing spindly and weak. Contrary to popular belief, a windowsill is not a good place for starting seeds indoors because the seedlings will grow sideways and spindly trying to reach the light, even if you turn the tray around every day. Also, the cold air coming off a window at night will slow germination and growth. 

Start seedlings under bright fluorescent lights. If you're do-it-yourselfer, you can use an inexpensive metal shelf unit and hang fluorescent lights from small chains between the shelves. Or you can build a shelf unit out of 2x2s (for the uprights) and 1x2s (for the shelf supports and slat shelves).

If you want to purchase one ready-made, I highly recommend the SunLite Garden. It's attractive, has lights that are very easy to adjust, and comes in several different sizes to suit your needs.

Give your seedlings 12-16 hours of light per day, but no more than this – they need a dark cycle, too. The lights should be adjusted so that they stay within 2-4” of the top of the seedlings. Raise the lights as the plants grow, and put the lights on a timer so you don’t forget to turn them on or off at the right time.


One of the biggest challenges to starting seeds indoors is finding a place that is warm enough, because most seeds need temperatures between 65˚and 80˚ F to germinate.

If you have a furnace room or other warm place, set your seed-starting shelves nearby. 

A terrific alternative is to use a seedling heat mat, which keeps seeds and seedlings warm, greatly speeding germination and growth and encouraging strong healthy plants. This is especially helpful for really slow-growing seedlings like peppers and parsley. Don't use a heating pad - even on low they get too hot for seedlings and are not built for wet environments. If you don't have a warm place or a heat mat, just start your seedlings a couple of weeks earlier.

Pots and Potting Mix for Starting Seeds Indoors

There are many different pots and trays to choose from for starting seeds indoors. If you're short on cash you can sometimes get  2" or 4” square plastic pots in flats from the recycle bin at your local nursery (ask first). Sterilize them in a mild bleach solution (1 part bleach, 10 parts water) before reusing them to prevent damping off fungus and other diseases from attacking your seedlings. You'll need the flats that the pots go in, too.

The best seed-starting trays I have ever used (and the ones I currently use) are Deep Root Seed Starting Trays. They are very durable and are reusable forever, and you can even get them with an optional self-watering mat and grow dome. I use a variety of sizes, because some plants, like onions (from seed), do well in the 40-cell size, but some plants need more room, like collards and chard, which I start in the 28s and later transplant up into the 15s as they get bigger. I will never have to buy seed starting trays again, because these will last forever.

Don't forget that the space on your shelves is at a premium, so it pays to optimize the number of plants you can fit there by using the smallest cell size possible, at least until it's time to transplant up. The 40s, 28s and 15s are all the same outside dimensions, and 3 of them fit perfectly into a boot tray, available from Lowe's or Home Depot.

I have also used newspaper pots, which work well too! There is a handy little paper pot maker tool that tucks the newspaper under at the bottom, and it's fun to make these in front of the TV in the evening. The newspaper breaks down quickly in the garden (and sometimes a little too soon indoors - but the roots tend to hold the soil together by that time), and once you have this tool, you'll never have to buy seed-starting pots again.

do not recommend using any of the disposable plastic systems that have to be replaced every year. Besides added expense, they aren't recyclable (and we're gardeners after all). I also don't recommend "compostable" or "plantable" peat or cardboard pots. They are quite slow to break down in the soil, and in the meantime they impede seedlings' roots from freely spreading out in all directions, which decreases overall plant size and harvest. Might seem hard to believe, but in 2011 I did a side-by-side comparison and my yields of peat-pot grown peppers was 30-40% less than that of the free-root transplants grown in the deep root seed starting trays. 

Planting the Seeds

The back of your seed packet will tell you how deep to plant each variety of seed that you have. A rule of thumb is to plant them about 3 times the diameter of the seed, but I have found it is generally better to plant seeds a bit shallower than recommended when starting them indoors..

Plant at least two seeds in each cell or pot as insurance against poor germination. If both seeds sprout and grow, snip off the smaller one to let the other grow strong without competition. Snip instead of pulling it out, so you don't damage the root of the one you're keeping.

Beginning gardeners sometimes have a hard time killing these little beautiful little seedlings, but your garden will be much stronger if you do this. (I always say a silent "thank you" to the one I’m culling, and either eat it or add its little stem to the compost, out of respect.)

Hardening Off and Transplanting

Our pampered little indoor seedlings need time to adjust to the great outdoors. They have to adapt to strong sunlight and wind, both of which stress plants and thereby make them strong.  DO NOT GET IMPATIENT NOW AND PLANT THEM OUT WITHOUT HARDENING THEM OFF FIRST. (Does that sound like the voice of experience? "But it's so nice out!")

About 10 days before you transplant your seedlings out, set the seed flats outside during the warm part of the day, in the shade at first, for a an hour or so. Every day for the next 10 days, increase their time outside and their exposure to sun. They will gradually adjust their “sunlight antennas” and strengthen their stems until they can take a full day of sun and wind without burning up or blowing over. 

Transplant them out at the recommended spacing on the seed packet. I always grow a few extra in case I need to replace any that don’t make it. (Sometimes they get eaten by birds or snails, or otherwise mysteriously disappear overnight).

Starting Seeds Indoors: A Matter of Timing

To figure out when to start your seeds indoors, find your average last frost date. Look this up on the internet, or check with your local state extension service.

Download the free "Starting Seeds Indoors Planning Chart" to figure out when to start different crops indoors. Click on the box above for the free chart (instructions for use are at the bottom of the chart).

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