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How to Start Seeds Indoors

By February 28, 2016 Garden Planning, Uncategorized

Many UFCO customers and other Front Range gardeners have been asking lately how to start their own seeds indoors. We’ve put together this blog post to help you with all the specifics! And now is the time to start thinking about it!

Why start your own seeds indoors?

  • Learn more! Starting your own seeds is very rewarding and you get to learn more about how plants grow, from start to finish.
  • More choice! There are thousands of tomato varieties out there and your local nursery might only offer 10 or 12. When you start your own seeds indoors you get to research and choose the perfect variety for your taste and your particular growing conditions.
  • Know what you’re getting! Lots of research has shown that the first few weeks of a plant’s life will greatly determine how healthy and productive it will be months later when you’re ready to harvest. When you start and care for your own transplants, you can be sure to give them all the attention that they need so you know you’ll get a great harvest later in the season.

What equipment do you need to start?


We buy our seeds from Johnny’s Selected Seeds and Fedco Seeds, because they have lots of variety, very consistently good product, and tend to be more affordable. Some of our other favorite seed companies are High Mowing Organic Seeds, Seed Savers Exchange, and Baker Creek. Or if you saved your own seed last summer, you’re all set!

Seed Trays

You can buy seed trays online or at a local nursery or hardware store. You can also use recycled yogurt containers or any other container that you can poke a hole through the bottom. If you do use any recycled product, make sure that you wash it out well before seeding, poke a hole or two in the bottom to allow for drainage, and make sure it is big enough (about the size of a personal yogurt cup is good). We like to put all of our seed trays/containers inside a larger tray or pan that can hold water, so that you have option of self watering your seed trays from below.

Soil Medium

Buy a good, organic seed starting mix from your local nursery or hardware store. Or you can make your own soil mix by combining your local soil with about 30% compost and 30% coconut coir (available at most nurseries). Make sure to not plant in too much compost or your mix will be too “hot” and could burn the seedlings.


You’ll need to have a good south-facing window to place your seed trays so they will get enough sun. If you don’t have a good south facing window, then you’ll want to get a grow light of some kind. You can buy a growing specific light online.


Seeds also need a little warmth to germinate and grow well. Don’t put your seeds in the coldest part of your house or out on your porch. Make sure they stay away from a strong draft. The warmth of your sun-filled window or your grow light should be adequate for growing your transplants. But if you want to go the extra mile, you can also buy a heat mat


You’ll need to water your seeds and eventually plants regularly. Since this is happening inside your house, using a watering can is difficult, so we like to water our seed trays with a spray bottle. Once your seeds have germinated and you have a bunch of little plants, you can also fill the pan under your seed trays with water and let your plants self water by the roots. 


OK, I’ve got everything I need. Now how do I start these seeds?

  1. Fill your seed trays or containers with your soil all the way to the brim of the containers. Water the soil in the trays either outside with a watering can or inside with many pumps with a spray bottle. You want the soil to be fully saturated with water.
  2. Using your finger, make a little hole in the center of the soil in each container/cell about 1/4” deep.
  3. Drop one seed into each hole. Seeds are small! But trust that each seed will germinate, so do your best to drop only one seed per cell. If you drop more than one, that’s ok – you’ll just want to thin later.
  4. Once all your seeds are placed, take a fresh handful of your soil mixture and sprinkle it on top of your trays, making sure that your seeds are fully covered.
  5. Water the seeds one more time with your spray bottle to make sure that the soil on top of your seeds is also wet.
  6. Place the tray in your south facing window or under the grow light and wait. Seeds will typically take anywhere from 3 to 10 days to germinate. During that time, monitor your soil moisture to make sure that it doesn’t dry out.

On-going transplant care

Once your seeds are planted, the only thing you have to do is make sure they get enough water and light. Feel the surface of your soil and make sure it is moist, but not too wet. If your plants are starting to wilt, that usually means that they are not getting enough water. If you are watering your plants from a pool of water in the bottom tray, the surface of the soil make not ever look wet, but if your plants look healthy and upright, then they are most likely getting the right amount of water.

If you are using a grow light, you’ll want to leave the light on for roughly 12-16 hours per day. If you are using a south facing window for light, keep an eye on your plants to make sure they are getting enough light. If your plants become “leggy” (tall and skinny like they are reaching for the light), then you don’t have enough sun in your window and you should consider getting a grow light to supplement.

Also keep an eye on your plants to make sure they don’t outgrow their cells or they will get “root bound”. If you plants become too big for their original cells, consider “bumping them up” (transplanting them) into larger pots indoors before moving them outside.

What does “hardening-off” mean?

Hardening-off is a very important part of the transplanting process! When it comes time to plant your transplants outside in your garden, you need to make sure they are adequately prepared for their life outside. You’ve grown your plants thus far in an environment free from wind, free from dramatic temperature swings and away from the full UV power of the sun. If you were to bring your plants directly outside from that environment, they would likely wilt and may die. So, you’ve got to ease them into it. About a week before you transplant them into your garden, bring them outside for short increments (slowly increasing the time) each day and then return them to their indoor home. This will ensure that your plants toughen up without wilting first.

If you need help transplanting, see our document: “How to Transplant”.

And when do I start my seeds?
Timing is everything! Here is a short list of common crops that will help you figure out when to start your seeds indoors.

TOMATOES & PEPPERS – Start seeds indoors anytime in the last two weeks of March (about 6-8 weeks before the final frost). Transplant tomatoes outside anytime after May 15th, after danger of frost has passed.

EGGPLANT – Start seeds indoors anytime in the second and third weeks of March (about 6-10 weeks before the final frost). Transplant eggplant outside after May 15th, when daytime temps are at least 65 degrees and nighttime temps are no lower than 50 degrees.

BROCCOLI, CAULIFLOWER, AND CABBAGE – Start seeds indoors anytime in the first two weeks of March for an early planting or in the last two weeks of March for a slightly later planting. Transplant outside anytime after April 15th, after the chance of a very deep freeze has passed. Plants should have 4-5 true leaves at the time of transplant.

GREENS – Greens like lettuce, kale, collards, chard, and spinach can all be direct seeded in your garden around April 15th or after, but some people like to get an earlier harvest by starting greens indoors. Start greens indoors around the middle of March. Transplant outside after April 15th, after the chance of a very deep freeze has passed.

For more info on how to plan your garden, see our Master Planting Document.


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  • Diana Nelson says:

    Great post! Found some great ideas here! I’m definitely recommending your ideas to my sister. She’s just beginning with her seed starters and I’m sure she’ll be very glad to have these useful tips on mind while working. Thank you for sharing this nice info. Happy gardening!

  • Shakti Vel says:

    Keeping the plants where it receives sufficient sunlight is very important. Thank you for the good article.

  • Raghu Kumar says:

    Plants are beautiful. No matter how depressed you are, just go and sit near the plants and you will feel better.

  • Mallory says:

    I love your website — I just read though A LOT of it. Thankful for your work and recommendations, and excited for the growing season to get here.

  • Margie says:

    Hello! Really good tips! I haven’t heard of Johnny’s Selected Seeds and Fedco Seeds yet, since few years I have been buying seeds from https://gardenseedsmarket.com/vegetables-en/ . There is also a big range of different seeds and they are really good quality. I have a small greenhouse bought in Ikea (probably you’ve seen it) where I grow my seeds. When they sprout I repot them to bigger pots. It’s amazing idea and thanks to it plants grow much more faster! I also have a special light for plants but of course natural sun is the best! Thanks for your post, hope mine ideas will be good for you too!

  • Don Davies says:

    Amazing! thanks for this! I’m planning to add some plants to compliment my Colorado Backyard landscaping. I want to add a little veggie patch so I can sustain the family with some vegetables! I think the soil there is arable and I hope I can make it work with these tips I got from you guys! Thanks again!

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