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  • Writer's pictureKassi Kuppinger

Starting Seeds Indoors: A Zone by Zone Guide

Embark on your gardening journey with confidence by mastering the art of starting seeds indoors. This essential practice lays the groundwork for a successful growing season, allowing you to cultivate a diverse array of plants from the comfort of your home. To ensure gardening success, it's essential to have the right tools and supplies on hand. From seed trays and potting mix to grow lights and heat mats, these essentials provide the optimal environment for seed germination and early seedling growth. With proper care and attention, you'll soon be rewarded with robust and healthy plants ready for transplanting into your outdoor garden. Delve into the world of starting seeds indoors and set yourself up for gardening triumph with this guide for starting seeds indoors in Colorado.

up potting seedlings into larger peat pots

Starting Seeds Indoors: Essentials for Gardening Success

Gardening in Colorado comes with a plethora of challenges one must learn to overcome. From our unpredictable weather and fluctuating temperatures to our short growing season and arid climate, starting your garden plants from seed indoors is essential if you want to have a thriving and productive garden.

The Growing Season

As we just mentioned, our growing season in Northern Colorado is short. It is generally safe to start planting after the average last frost date, which is often marked by Mother’s Day or sometime around the middle of May. While the weather is generally warm enough, this date is an average and there still is a slight chance of frost. (Pro tip: It is always recommended to keep some frost cloth handy just in case freezing temperatures roll in unexpectedly.) The first average frost date for Northern Colorado is generally around the end of September/beginning of October. So, this gives Colorado gardeners just around four months of quality growing weather. For some plants with longer maturity dates, however, this is not quite enough time. By the time they start to produce a steady stream of produce, the season will be nearly at its end. This is where the practice of seed starting comes into play. Seed starting indoors allows those plants with longer days to maturity to get a head start on the season, ensuring that you will get a full season of produce from them.

Tools and Supplies for Seed Starting Indoors

Having the right tools and supplies for seed starting is imperative. It is important to use seed starting mix or pellets specifically made for seed starting. You will also want trays with clear plastic covers to help keep in moisture and create an environment similar to that of a greenhouse. Keeping your seedlings warm is also so important. Seedling heat mats keep your growing environment at the perfect temperature to help encourage germination and the growth of your plants. As your plants grow, you will also eventually have to increase the pot size. Peat pots are

seed starting supplies from local garden center

great for this, as they are biodegradable and make upsizing, as well as transplanting into your garden, a breeze. Other tools such as misters and grow lights can also make a huge difference in your seed starting endeavors. Here is a list of recommended seed starting tools and supplies:

The Benefits of Starting Seeds Indoors

Give Your Plants a Head Start

Starting your garden plants from seed indoors means that by the time the weather has warmed up enough to plant things outdoors, your garden fruits and veggies will already have had 6-8 weeks to grow, giving them a jump on the growing season, meaning that you get more produce quicker and for longer.

More Options for What You Can Grow

Another benefit to starting your crop from seed is that there are so many more options for what types of fruits and vegetables you can grow. Buying plant starts from your local garden center is an easier alternative for some, but this limits you to growing only what plants are in stock. Plus seed packets are a fraction of the cost and provide you with seeds to last multiple growing seasons.

Seed Starting is Less Expensive

As we just mentioned, the alternative to seed starting indoors is purchasing plant starts from your local garden center. However, due to the time, energy, and resources put into growing plant starts, they tend to be significantly more expensive than seed packets.

Greater Sense of Achievement

Growing all of your garden plants from seed, while not an extremely difficult task, creates a massive sense of achievement. There is nothing quite like looking out over your garden mid-season and seeing everything you fostered from seedlings into the beautiful and productive plants they are today.

How to Start Seeds Indoors in My Zone?

If this is a question you have come across, the answer is simple. If you are starting your seeds indoors, the hardiness zone you are in does not matter, because it is indoors. Hardiness zones only affect plants when planted outdoors, so the only time you would need to take into consideration the planting zone you are in is when moving your plants from inside your home to out in your garden. The first and last average frost dates will vary from zone to zone, and certain plants may grow better in some zones and not in others. The state of Colorado consists of zones anywhere from 3b to 7b depending on if you are high up in the mountains or down in the desert, though the majority of the state sits mostly in the USDA plant zone 5 and 6. So, regardless of what zone you find yourself in, the process of starting garden plants from seed indoors will be the same. What will be different is what types of plants will thrive in your climate and when it is safe to move them outside. Be sure to do your research based on what USDA hardiness zone you live in, or visit your local garden center and nursery for information on your zone and what you should plant.

If you are looking for a step-by-step guide on how to start your seeds indoors, check out our blog, "Seed Starting Basics: The Importance of Starting Seeds Indoors in Colorado", to find all the information you need to start your seeds from scratch and get ahead of your spring gardening.

Which Vegetables Take the Longest to Grow from Seed?

rack of seed packets in local garden center

Several vegetables have longer days to maturity, meaning they take a longer time to grow and produce harvestable crops. These vegetables require patience and careful planning, but the delicious and nutritious harvest they provide is well worth the wait. Some of the vegetables with the longest days to maturity include:


Most varieties of tomato seeds require around 80 days to reach maturity and start producing fruit. Generally the larger the variety the longer the days till maturity.

Winter Squash

Varieties like butternut squash, Hubbard squash, and spaghetti squash can take anywhere from 80 to 120 days to mature, depending on the variety and growing conditions.


Pumpkin seeds typically require around 90 to 120 days to reach maturity, with larger varieties often taking longer to grow.


Most pepper plant seeds also take somewhere around 80 days to reach maturity. Many varieties can be harvested early, however flavor and nutritional value will be higher if they are allowed to ripen fully.

Brussels Sprouts

Brussels sprouts are slow-growing vegetables that can take around 90 to 110 days to mature. They are often grown as a fall crop, as cooler temperatures improve their flavor.


Globe artichokes are vegetables that can take up to 150 days or more to reach maturity from seed. They require a long growing season and may not produce harvestable buds until the second year of growth.


Leeks have a long growing season and can take anywhere from 90 to 120 days or more to reach maturity. They are often planted in early spring for a fall harvest.


Rutabagas are root vegetables similar to turnips and can take around 90 to 120 days to mature. They are often planted in late spring for a fall harvest.


Garlic is another garden plant that has a rather long maturity period, taking anywhere from 120-150 days to reach maturity. This garden plant is usually planted 4-6 weeks before the average last frost and is generally ready to harvest by the end of the growing season.


While easy to grow, potatoes can take a while to reach maturity, averaging around 80-100 days depending on the variety. Plant your potatoes early in the spring for a fall harvest.


When started from seed, eggplant can also take anywhere from 100-120 days to reach maturity. Due to this long maturity period, it is ideal to start this garden plant from seed indoors 6-8 weeks before the start of the growing season.

Set Yourself Up for Success with Seeds from Bath Garden Center

At Bath Garden Center & Nursery, we are here to help with all your gardening needs! From seeds and supplies to gardening tools, plant material, and more, our Garden Center is truly your one-stop shop for all of your growing endeavors. If you have questions or need help, feel free to visit us in-store. You can also give us a call or fill out a contact form. We look forward to assisting you!


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Jun 27

Explore the realm of indoor dordle seed beginning and equip yourself for success in gardening with this guide on indoor seed starting in Colorado.

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