If you’re planning to grow a garden this summer, odds are you intend to start at least some of your plants from seed. Here in Colorado, with our short growing season and unpredictable weather (such as the 70 degree drop last week), it’s worthwhile to start a lot of those seeds indoors.

I’ve written a lot of posts about growing plants from seeds, and I don’t want to repeat myself, as you can still read them (check the category list at right), and I hope you will. But of course not everyone reads my blog! Every day on my Facebook gardening group, I see frustrated would-be gardeners with weak, floppy seedlings, wondering what they did wrong. I realized it’s usually one of four things.

They started too early. It’s a bit of an art, knowing when to start your seeds. Last year, we had a huge snowstorm at the end of May. Other years, frosts give way to warm weather at the end of April. There’s a bit of guessing, but it can be an educated guess. Know your average last frost date. Look online, and then ask some experienced local gardeners what they think. Your county master gardeners are another good source of information. (I checked several websites and found huge discrepancies for my zip code—from May 4 to June 16! That’s probably because the elevation of Colorado Springs varies by over 1,000 feet from the south end to the north end.)

Some flowers and vegetables are able to shrug off a bit of frost, while others die at temperatures in the mid-30s. Don’t rush things—once a plant is overly chilled, even if it survives, it will never live up to its potential. Know what temperatures your seedlings will be able to handle. I plant cool-season species (cabbage family plants, onions, lettuce, violas, etc.) right around my average last frost date, and wait another two weeks before setting out the more finicky warm weather plants, such as basil, tomatoes, and squash.

Once you know what date you intend to transplant your seedlings into the garden, count backwards to know when to start the seeds. Most veggie transplants take 6 to 8 weeks—peppers a little longer, squash and cucumbers much shorter. I’ve put together a summary of planting dates for the Pikes Peak region, but it can be adapted to other parts of the country by adjusting according to your local frost dates.

They kept the seedlings too warm. While most garden seeds germinate best from 70° to 80° F., it’s better to grow the seedlings at cooler temperatures. I keep mine in the basement. It’s heated, but it’s the coolest part of the house, averaging around 60° to 65° F. Warm seedlings grow too quickly, and end up as wimps.

They didn’t provide enough light. Windowsills are convenient, but it’s hard to find one with just the right amount of sunlight, especially since the glass windowpane magnifies its intensity. If your seedlings have bleached leaves, it’s likely they’re getting too much direct sun. If the plants are leaning toward the outdoors, the light level is insufficient.

I much prefer to use artificial light. Now that shop lights have LED bulbs, they’re the perfect solution. I use two fixtures, placed next to each other, which provides space for two standard seed trays underneath. I use a timer to turn them on and off, giving them about 13 hours of light per day. (Longer “days” can program my lettuce to bolt.) Keep the growing plants as close to the light source as possible.

They didn’t let the seedlings move. Plants would normally be exposed to breezes ruffling their leaves. This movement of their stems and leaves tells them to toughen up a bit, and they’ll grow stronger and stockier. My basement doesn’t have a breeze, but I do own a fan. I’ve aimed mine at my light set-up, turning it on low—just enough for a gentle zephyr.  Another alternative is to frequently “pet” your plants, lightly running your hands over the tops. I was surprised what a difference movement makes.

One last note: you’ll notice that many of the seedlings in these pictures are rather large, considering that I won’t be planting them outside for a while yet. Yes, I started them early. That’s because I’m willing to keep moving them into larger pots as they grow, and then at some point start hauling them outside every day that the weather cooperates, bringing them back indoors for most nights. That’s a lot of work, but I consider it worth the effort.