A Guide to Starting Seeds Indoors

 

 

 

Starting your warm weather crops such as tomato and vegetable seeds indoors has many advantages. You can get a head start on the growing season, you can choose from a wide range of varieties, and you can control the quality of your plants from seed to harvest.

  

When it comes to starting seeds indoors in the spring, knowing when to start is one of the most important elements. Begin by understanding the hardiness zone you garden in. Sometimes called growing zones, USDA zone hardiness maps are based on winter temperature averages over a thirty-year period. The intent is to help gardeners make informed decisions regarding which plants will perform well in their geographical area.

 

While primarily aimed at trees, shrubs, perennials, knowing your hardiness zone is useful for your vegetable garden as well. The 5 zones represented in Colorado are 3, 4, 5, 6, 7. The mountains are predominantly Zone 4, the fruit growing area near Grand Junction is 6-7 and the Front Range predominantly Zone 4-5. Longmont Plant Hardiness Zone is 5b and Estes Park is Zone 5a. 

 

A normal growing season is 146 days (about 5 months). This number assumes that season extenders such as frost cloths or cold frames are not used. As a rule, May 15 (May 30 if you garden at altitude) is the start of our frost-free growing season. Some years we’ve been able to plant as early as Mother’s Day, other seasons it’s after Memorial Day. Last year, for example, we had our last hard frost on May 4, followed by a quick warm up. In 2022, we experienced light snow and 27° on May 22. In 2021, we had a hard frost on May 20. October 1^st is the average first Fall frost. The point is you should always be prepared to deal with our unpredictable spring weather.

 

Using May 15 and the information on the back of the seed packets you’ve selected will help determine the date you’ll want to start your seeds indoors. Example: Peppers should be started eight to ten weeks before last spring frost. Ten weeks before May 15 is the week of March 7.  

 

Begin the process by choosing high quality, fresh seeds from local suppliers. Check the back of the seed packet. There should be a 2024 date printed on it. This is your assurance that the seed is fresh. 

When you open the seed packet you should find seeds that are uniform in size and color. Selecting premium seeds will give you better germination rates and stronger seedlings.  

 

Take time to read the seed packet. You’ll find valuable information regarding planting depth, spacing and days to emerge on the outside of the packet.   

 

In addition to seeds, you’ll need containers, domes, labels, and seed starting medium. When it comes to containers, plastic seed starting trays and inserts are the more traditional method for starting plants from seed. You fill the plastic cells with seed starting mix, then plant seeds in them. This method works very well, and you can choose from several different inserts.   

 

An alternative method would be to use peat-based containers. An advantage to growing in peat pots is once your seedlings are ready to be moved to the garden, peat pots can be planted directly in the ground, which reduces transplant shock.  

 

Domes help hold in moisture and warmth while your seeds are sprouting. Domes are available in two inch and seven inch sizes. Once your seeds have sprouted and have two sets of true leaves, remove the domes to allow air circulation.  

 

It’s important to label trays, so you’ll know the variety of seed you’ve planted. Labels are available in wood or plastic, and they can follow your seedlings from the starting tray right into the garden.  

 

Now that you have selected your seed starting trays, inserts, and domes, pick up some seed starting mix. Use seed starter, not potting soil or garden soil. Seed starter mix is sterile and holds moisture well. You'll have much better results with seed germination. It's a good idea to moisten the seed starting medium before you sow your seed.  

 

For quicker germination and stronger root systems, buy a heat mat. Heat mats keep the seed starting soil temperature constantly warm, even as the grow room cools off in the evening. Keeping the soil at a constant temperature promotes faster germination, larger root systems and sturdier plants.   

 

Starting tomatoes and vegetables from seed is a great way to get the variety of vegetables and tomatoes you want. Using the best seed and seed starting supplies will help ensure better, stronger transplants when it does come to time to move your seedlings out into the garden.