How To Start Seeds Indoors

Updated Dec 27, 2022

Whether you are just starting some herbs to keep indoors or getting ready to plant your seasonal garden, there are a few important steps to follow when you are starting your seeds indoors. This article will outline the steps to get your seeds ready for transplanting outdoors when they are started from seed indoors.

Preparation

Step 1: Select Seeds - To get your garden started, you must first plan out what you want to plant. Once you know what you are planting, then you can get your hands dirty. When preparing your seedlings for planting in the spring, you will want to start most seeds 6-8 weeks before your last spring frost. You can find the approximate days to maturity on your seed packet. For flowers and vegetables that are commonly directly sown into the soil, this number will reflect the number of days to maturity from your planting date. For vegetables that require starting indoors ahead of time, this number reflects the days to maturity from transplanting. These include tomatoes and peppers. For a list of what plants do best when directly sown vs started indoors, check out the article "When Should You Start Your Seeds Indoors?"

Step 2: Select Your Container or Tray - After selecting your seeds, you will want to select the right-sized container to grow them in. Generally, it is best to start vegetables in the container they will be transplanted from. This reduced the number of times their root systems were disturbed. Flowers are often started in smaller containers to reduce the amount of space they take up during the germination process.

To start vegetable seeds, we recommend using an 18-cell insert (3.5-inch pots), 72-cell insert (12 groups of 6 connected 1.3-inch cells), 36-cell insert (6 groups of 6 connected 2.25-inch cells), or a 32-cell insert (8 groups of 4 connected 2.25-inch cells). For starting many flowers at one time, we recommend using a 288 plug tray (dibble tray). This will allow you to save space when germinating with the use of bottom heat, and to transplant seedlings that have already germinated into one of the above-mentioned inserts for continued growth. For a fun family activity, try starting some seeds in DIY newspaper pots or cardboard egg cartons.

Step 3: Select Your Soil - Potting soil is most commonly used; however, this will require you to add additional nutrients. Alternatively, you may also use Minute Soil+ Amended Coconut Coir to provide the needed nutrients to support your seedlings' nutritional needs. A simple potting soil or the original Minute Soil may be used for the 288 plug tray. Additional nutrients are not required until after your seeds have germinated, at which point you will need to transplant these plugs to a larger container anyways.

If you are only starting a few seeds, you may want to consider using our Jiffy-7 Peat or Coconut Coir Netted Pellets. These make the starting and transplanting process a breeze. Simply hydrate the pellet of soil and plant your seeds at the appropriate depth. All our inserts can be placed inside our 10x20 1-inch or 2.5-inch deep extra-strength trays for easy transportation and drainage after watering.

Planting

Step 4: Sowing Seeds - Now it's time for the fun part! When planting your seeds, you should follow the recommended seed depth printed on your seed packet. If you don’t see a depth listed, there's no need to worry. Simply plant your seeds at a depth 4 times the width of a seed. It should look like 3 seeds could sit on top of yours. If planting older seeds, or ones known to have a lower germination percentage, sow 2-3 seeds per cell. You can always go back and thin to 1 seedling per cell after germination, if needed. If you have a hard time handling small seeds, you may consider using a seeding tool. Some seeds can benefit from being soaked for 4-6 hours to soften the seed coat for germination. Generally this extra step is not as beneficial for very small seeds. If you can easily strain the seeds from the water, go ahead and give it a try.

Step 5: Add Bottom Heat - Most seeds benefit from warmer soil temperatures during the germination process. We recommend using a germination heating pad to maintain temperatures of 68-86 F. This helps to increase germination rates and prevent damping off. After germination, you usually want to keep the temperatures about 10 degrees cooler. For more specific temperature recommendations, take a look at your seed’s product page online.

Step 6: Water - The seedlings need consistent watering to thrive. Avoid watering on the leaves, but rather directly on the surface of the soil. The soil should be the consistency of a damp sponge. If the plant isn’t getting enough water, it will wilt. Until your seedlings are well-established, water is the most important growth factor. Be aware of how quickly your soil dries when on a heating mat or with increasing spring temperatures. One missed watering at the wrong time can be devastating to a new sprout. One of our favorite tools for watering is the Pump Pressure Water Sprayer Bottle.

Step 7: Lighting - After water, light is the next most important growth factor. It is important to make sure your seedlings have access to light as soon as they have sprouted leaves. This allows them to start storing and using energy outside their seed reserves. It will also help their stems to strengthen in preparation for any transplanting that will take place. When using grow lights, keep in mind it is best positioned 2-4 inches above your plant tops (running on 12-16 hour cycles). As your plants grow, adjust the grow light to maintain the 2-4 inch spacing. For growing several trays indoors, try using a growing rack with adjustable light fixtures.

Harden Off

When the weather starts getting warmer outside (above 45 degrees), you may be tempted to put your baby plants in the ground or simply leave them on the porch. It is important to gradually introduce your plants to the outdoors. This process is called hardening off. Start by bringing the plants outdoors for 1 hour on the first day, then bring them back indoors. Increase the time outdoors slowly until they are spending most or even all of the day outside before you transplant.

Plan ahead so you are not rushing this important step. Otherwise, your plant starts may die, have stunted growth, or otherwise suffer. This gentle building of time spent outdoors allows the young plants to develop a "thicker skin" suitable for protecting the plant from the elements and natural, small fluctuations in temperature.

Transplant

When your plants are strong enough and have been sufficiently hardened off, it is safe to plant your plants outdoors (according to your seeds’ planting instructions). Now you are ready to transplant! Make sure your garden soil is well prepared, and you have amended the soil if needed. Make the hole in your garden space and carefully remove your plant with its soil from the transplant container. Gently break up the root ball and put it in the ground or pot. Water thoroughly. If planting in the early spring, keep an eye on changing temperatures. If a frost is coming, be sure to lightly cover your new transplants until they have rooted out in their new location. If temperatures suddenly increase, be sure they are getting enough water throughout the day.

Other Contributing Authors:

Ashleigh Smith, True Leaf Market Managing Editor