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  • Writer's pictureKassi Kuppinger

Seed Starting Basics: The Importance of Starting Seeds Indoors in Colorado

Starting your garden plants from seed indoors is a necessity in Colorado. Our short seasons do not allow certain plants like tomatoes and peppers enough time to mature if grown from seed outdoors. This is also why many people purchase starter plants from Garden Centers like our own! However, starting your own plants from seed is fun, rewarding, and gives you something to do in the cooler months leading up to spring. So, let's dive into the basics of seed starting indoors!

When To Start Garden Plants from Seed Indoors

Generally, you want to start your plants from seed 6-8 weeks before the average last frost date, which is usually sometime around mid-May. That means you should start your seeds indoors sometime around the middle of March. Certain plants may have longer or shorter maturity periods, so based on this, some seeds may not need to be planted quite this early. When you are selecting your seeds for the gardening season and planning out your garden, take note of the instructions on the seed packet for guidance on how early to start your seeds indoors.

What Seeds Need to be Started Indoors

Plants that have longer maturity periods need to be started from seed indoors. Plants like tomatoes, peppers, watermelon, broccoli, cauliflower, and eggplant are just a few examples of garden fruits and vegetables that will need a little bit of a head start. Other garden plants such as lettuce, spinach, beans, cucumbers, or squash do not necessarily need to be started from seed. These plants generally grow fast enough that they mature in plenty of time to provide you with a bountiful harvest. Other vegetables such as radishes, beets, carrots, turnips, and other root vegetables should not be started from seed indoors as transplanting them outside can be difficult and is likely to disrupt their root growth. If you are ever wondering which garden vegetables should or shouldn't be started from seed, the back of the seed packet will likely have instructions or information. You can also always come into Bath Garden Center and we can give you specific information on how to grow any of the seeds we sell here in Colorado.

How To Start Garden Vegetables Indoors

While seeds do require very specific circumstances to be able to germinate and grow successfully, all of the different products and tools out there have made indoor seed starting quite simple. Follow these simple steps and get your garden fruits and veggies growing in no time!

Select A Container

There are so many different options when it comes to what container to choose when growing your garden starts indoors. Many miniature greenhouses come with biodegradable peat pots that can be replaced year after year. Others come with little peat pellets that are easy to use and replaceable. Such miniature greenhouses come in a variety of sizes from 50-cell greenhouses to 12-cell windowsill greenhouses and everything in between. The size you pick depends entirely on the number of different plants you intend to start from seed. One benefit of such containers is the biodegradable peat pots and the biodegradable netting around the peat pellets make it so that you can plant your seedlings directly into the ground without having to worry about removing the container. The peat pot will simply decompose into the soil around the plant and will not hinder the growth of roots after it is planted in your garden. Here are some popular options for seed starting greenhouses and their replaceable pots/pellets:

50-Cell Seed Starting Greenhouse with Biodegradable Peat Pots & Refills:

50-Cell Seed Starting Greenhouse with Peat Pellets & Refill Pellets:

What Soil to Use When Starting Seeds Indoors


If you choose to use a seed starting greenhouse with peat pot inserts, you will want to be sure to use the correct soil. Seed starting soil, while it may seem like an unnecessary purchase, is best for starting seeds indoors. Seed starting potting soils are much less dense, and this helps the seedlings establish strong root systems since their roots will not have to work as hard to penetrate a heavy or dense soil mixture. Such potting mixes usually also have some nutrients mixed in which also help the seedlings grow strong and healthy. Once you obtain the seed starting potting mix of your choice, moisten the soil slightly. You can do this by spraying the soil with a spray bottle before filling your peat pots. You want to soil to be evenly moist, but not soggy or oversaturated. Once you've reached this level of moisture, fill your peat pots and lightly pack down the soil.

Plant Your Seeds

Once you have all of your greenhouse cells filled with seed starting soil, it is time to plant your seeds! You will want to plant 2-4 seeds in each cell or peat pellet. Planting more than one will ensure that at least one of the seedlings germinates and begins to grow. If all of them do, then you can pull the weakest seedlings and leave the strongest one to grow. Most seeds do not need to be planted very deep, and often setting them on top of the soil and lightly pressing them into the surface is enough. Each of your seed packets will have detailed information on how deep to plant them, and every different type of seed will have different requirements, so be sure to pay attention to this detail!

PRO TIP: Don't forget to label your cells! It is very easy to get to planting and forget which seeds you planted where, and when they are just sprouting, it is very difficult to tell the difference between them! So, pull out some popsicle sticks or plastic plant labels and write down what you are planting as your go.

Where To Keep Your Seedlings


Now that your seeds are planted, it will be very important to keep them somewhere warm. The seeds you planted will need soil temperatures around 70 degrees Fahrenheit in order to germinate. Some people place their seed starting tray on top of their fridge or in a warm window. Our suggestion is to purchase a seedling heat mat. These mats are usually the same size as many popular seed starting greenhouses and are easy to use. Simply plug them in and set your seed starting tray on top of it. This will ensure that the soil stays at the perfect temperature to trigger germination and will help the roots of your seedlings grow strong and healthy.

How To Water Seedlings

It is best for the soil to stay slightly moist. Like with anything, super soggy or oversaturated soils can cause the plant to die. Similarly, soil that is overly dry will cause your seedlings to shrivel up and die also. Many seed starting greenhouses come with a dome or cover that helps to keep in moisture. Especially in Colorado where the climate is very dry, we highly recommend this! We also recommend watering with a spray bottle. This allows you to water more consistently and also avoids your seeds or seedlings from being displaced by a heavy stream of water. So, if you notice your soil is looking a little dry, give each cell a spritz or two of water and keep your plastic dome covering your seedlings to keep in warmth and humidity.

How Much Light Do Seedlings Need?


Your seeds will not require a lot of light right after you plant them. However, after they begin to sprout, your seedlings will require at least 8 hours of sunlight in order to grow strong and healthy. Placing your seed starting tray in a sunny window is best, though if you do not have a south or west-facing window, you can provide supplemental light in the form of a grow light. Maintaining this amount of light for the entirety of their time growing in your home will be very important if you want big plants. Keeping your seedlings on a seedling heat mat will also continue to be very helpful in stimulating strong root growth.

Increase Pot Size Periodically

As your seedlings grow, they will very quickly outgrow their original containers. When this happens, it will be necessary to up-pot your seedlings into larger peat pots so that their growth is not restricted and they can continue to grow big. You will know when it is time to repot your seedlings if you begin to see roots poking out the bottom drainage holes of any peat pots you used. This is a sign that your plants are searching for more space to grow. In general, you will want to go up by just one pot size. Planting in too large of a pot can bring about issues with overwatering. Keep a close eye on your plants and up-pot them as needed. Your plants may need to be up-potted 2-3 times before they are ready to be moved outside. If you choose to plant your seedlings in biodegradable pots, your seedlings do not need to be removed from their current pot to be planted in a larger pot. Simply place the seedling, peat pot and all, in the next size up and fill in any extra space with soil. That is the beauty of using biodegradable peat pots!

When To Plant Seedlings Outside

It is usually safe to plant any frost-tender garden vegetables or fruits outside after the average last frost date. This is usually around Mother's Day or early to mid-May. The average last frost date is just an average, though, and this does not mean that there is absolutely no chance of experiencing a late frost. So, keep an eye on the weather and be sure to cover any plants if low temperatures are in the forecast. It is also never a bad idea to harden off your plants before you plant them in your garden outside. Such an abrupt change could cause the plants you've worked so hard to grow from seed to go into shock. Harden off your plants by placing them outside for a short period of time each day. Increase the time they are outside by a small amount each day until they are outside for a full day. This will greatly reduce the amount of shock they experience when they are transplanted into your garden.

Seed Starting Questions

If you have any questions about how to start seeds indoors, what grows well in Colorado, or any other questions pertaining to gardening in Colorado, let us know! We are always happy to help. If you need some ideas in terms of what to plant, check out our blog on The Best Vegetables for Your Colorado Garden, or you can shop seeds and seed starting supplies in-store or online!


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