Get a jump start on your vegetable garden by starting seeds indoors. Here’s what you need to know to successfully start your plants indoors so you will be ready to dig in when spring arrives.
Starting seeds indoors allows you to enjoy gardening months before the planting season begins. Herbs, such as basil, mint, and thyme, can be easily started indoors. You can use herbs in the kitchen long before it’s warm enough to plant them in the garden. Microgreens are some of the easiest and fastest plants to grow indoors. You can harvest microgreens in just a few days after germination. In addition, there is a vast selection of seeds to choose from. Expand the diversity in your garden and grow fun and unusual vegetables, such as green eggplant or orange cauliflower.
Some Seeds Need A Head Start
Northern Illinois has a short growing season. The last frost date for our area can be as late as Memorial Day weekend, and the first frost date is as early as the last week of September. Slow-growing tender annuals, such as tomatoes, peppers and eggplants, need to be started indoors so they are ready to harvest during our summer months. Slow-growing, cold-tolerant vegetables such as broccoli, cauliflower, cabbage and celery need a head start indoors so they can be transplanted in early spring and harvested before it gets too warm.
Seed packets indicate the number of weeks before your last frost date to start planting indoors. To look up your average frost dates, you can enter your zip code here. Some seeds should never be started indoors, and their packets will usually advise you if it’s not recommended. These include vegetables such as radishes, carrots, beets and corn. They generally do not transplant well into the garden and are best sown directly into the ground based on your frost dates.
What You Need to Get Started
You can buy new seeds every year. If you have seeds from last year, use them! Last year’s seed packets will still contain viable seeds as long as they were stored in a dark, cool, dry location. After a year, the number of viable seeds will decrease over time and varies greatly based on the type of seed.
You can also save seeds from the best plants in your own garden by drying and storing the seeds at the end of the season. Tomatoes, peppers, beans and peas are the easiest to save because they are self-pollinated, so they don’t need a male and female flower to produce fruit. Pumpkins, squash, cucumbers and corn cross-pollinate easily with other plants by insects and wind so it is not recommend that you save seeds from these plants.
Viability Test for Old Seed Packets
• Place ten seeds on one half of a warm, damp paper towel and fold the other half over to cover, making contact with the seeds.
• Place them in an open container to store in a dark, warm location. Spray the paper towel regularly to maintain moisture.
• Count how many seeds sprouted within the germination time frame on the seed packet.
• If 8 out of 10 seeds germinated, that’s an 80% germination rate, which is quite good.
Soil & Containers
Use a sterile, soilless medium that contains no field soil or fertilzers. You can use a seed starting soilless mix or our TGP Choice Potting Mix will also work just fine. The growing medium needs to stay damp but not soggy. It’s important to use a container with sufficient drainage holes. You can purchase seed growing kits, or use items you have around the house. Add some drainage holes to plastic cups or yogurt containers and set them on a cookie sheet or aluminum tray to make your own seed starting kit. Thoroughly sanitize your containers before adding your soilless medium.
Peat pots, paper towel rolls and homemade newspaper pots are great for plants that are more sensitive to transplanting. These containers can be planted with the seedling directly in the soil as the material will decompose without disruption to the root system.
Light & Heat
Seeds need a dark, warm location until they germinate. Tomatoes and peppers germinate better in warm soil. Heat mats placed under your seed trays will keep the soil warm warm, but average home temperatures are warm enough for successful germination.
Once your seeds have sprouted, it’s important that they receive sufficient light. A sunny south-facing window is not enough for these young plants. You will end up with very weak, leggy seedlings like the ones pictured below. It’s best to place a bright, white light directly over your seedlings for 14-16 hours each day. You can purchase light kits specifically for seed starting or you can create your own set up with a simple shop light and shelving. Whichever you decide to use, it’s important that the height of the light can be adjusted as the plant grows. Keeping the light 1-2 inches above your young seedlings will result in strong, sturdy stems.
Seed Starting Tips
Follow the directions on the seed packet with regards to the depth of the seed. Planting your seeds too deep or too shallow can result in poor germination. Each seed is different depending on the size and variety of the seed. Some seeds need extra steps to aid the germination process and are usually indicated on the seed packet instruction. Cold stratification is the process of exposing seeds to cold, damp conditions to encourage germination. Seed scarification is the process of weakening the seed coating by scraping or nicking it to speed up germination.
Covering the newly planted seed with a clear plastic cover, such as plastic wrap, will help retain heat and moisture to create a greenhouse effect that is ideal for germination. As soon as your seeds have sprouted, remove the plastic covering and place under your lights. The first leaves you will see are called cotyledons. These long smooth leaves are the seed leaves and not the true leaves of the plant.
It’s best to water your seed starts from the bottom. We recommend placing your containers in a tray and add a little water to fill the bottom of the tray. The water will be absorbed from the bottom of the container through the drainage holes. Be careful not to add too much water. You don’t want your containers to be sitting in water for days either.
Once a few true leaves have formed, it’s a good time to thin out weaker seedlings if you planted more than one seed in the same container. Never pull out the seedlings when thinning as it can disrupt the new root system that is developing. Instead, cut them at the base with clean pruning scissors. Thinning is necessary to allow more room for the seedling to grow and prevent disease.
Repotting & Fertilizing
If you start to see roots coming out of the bottom of the container or your seedling is roughly twice the height of the container, you will need to repot your seedlings into larger containers. This is also when you can introduce a standard garden or potting mix that contains some nutrients for the plant. Wait two to three weeks after repotting before introducing a liquid fertilizer. Too much fertilizer at this stage could damage your young seedlings, so dilute to half the strength and apply only once every other week.
Hardening off is the transition period plants need to acclimate from their indoor growing conditions to the outdoors. Over the course of a week, gradually increase the amount of time your seedlings spend outdoors to get them acclimated to the fluctuating temperatures, sunlight and wind. This is an important step that will help your plants thrive once planted in the garden.
The Winter Farmhouse Popup at our Aurora location is open every Friday, noon to 4pm, and Saturday, 10am to 2pm throughout the month of February where you will find a wide selection of herb and vegetable seeds as well as plant labels and other seed starting supplies.
Join us for a free virtual class on February 25 at 11 am where one of our veggie experts, Cynthia, will help you maximize your veggie garden production with layout tips, the benefits of different soil amendments, which veggies do well in our area and how to take care of them. No registration is required. Link to free virtual class here.