Starting seeds indoors is a fun and rewarding activity for gardeners of all levels. With a little bit of planning and care, you can grow healthy, strong seedlings that will thrive in your garden. It’s a great way to get a jumpstart on your garden and extend your growing season. It's also a fun and rewarding activity for gardeners of all levels.
Grow Strong, Healthy Seedlings
Starting seeds indoors is one of the most satisfying ways to get a head start on your garden—and it’s easier than you might think. This post will walk you through every step: from selecting seeds to preparing soil, to caring for your seedlings—and finishing with “hardening them off” before planting outdoors. Deep Roots uses a 1:! mix of our microbe-rich compost and worm castings as our potting soil, not shown in this video.
Why Start Seeds Indoors?
Whether you're growing tomatoes, peppers, herbs, or flowers, starting your own “transplants” (another word for seedlings) can save you money, expand your variety choices, and give your garden a healthy early boost.
By starting seeds indoors in early spring, you can give summer crops like tomatoes and peppers the head start they need to be productive all season long. It’s a great way to extend your growing season and get hands-on with your garden early in the year.
Follow These Simple Steps
Step 1: Choose the Right Seeds
Not every plant needs to be started indoors. Focus on varieties that need a longer growing season and benefit from transplanting, such as tomatoes, peppers, many herbs, and flowers. Choose seeds that are fresh, high quality, and well-suited to your growing conditions. You can buy them from local nurseries, trusted online seed retailers, or even seed swaps with other gardeners.
Step 2: Gather Your Supplies
To get started, you’ll need a few essentials. These include containers to plant in, such as seed trays or small pots with drainage holes. For an eco-friendly option, consider biodegradable pots made from materials like peat, coir, or paper—these can be planted directly into the garden without disturbing the roots. Your potting mix should be rich and alive; we recommend a blend of half microbe-rich compost and half worm castings. You’ll also need a light source—grow lights work best, since windows typically don’t provide enough consistent sunlight indoors. Keep a spray bottle or watering can nearby to keep the soil moist.
Step 3: Plant Your Seeds
Fill your containers with the compost and worm casting mixture, leaving about a quarter inch of space at the top. Gently press down the soil to remove any air pockets. Follow the seed packet instructions, but a general rule is to plant seeds about a quarter inch deep and place two to three seeds per cell or pot. Cover the seeds lightly with more soil and water gently. Be sure to label your trays so you know which plants are which.
Step 4: Provide Proper Light
Most seedlings require 12 to 14 hours of light per day to grow properly. A grow light is your best bet to provide this kind of steady illumination. While it might seem convenient to use a sunny window, it usually doesn’t provide strong or consistent enough light to keep your seedlings healthy. Without enough light, seedlings may become weak and leggy.
Step 5: Care for Your Seedlings
Once your seeds have germinated and begun to grow, keep the soil consistently moist but not soggy. As they get taller, thin them out by snipping the weaker seedlings and leaving the strongest one in each pot. Eventually, your seedlings will outgrow their starter pots. At that point, transplant them into slightly larger containers filled with fresh compost and worm castings. This gives their roots more space to grow and prepares them for life in the garden.
Step 6: Harden Off Your Seedlings
Before you plant your seedlings outdoors, you’ll need to harden them off. This means gradually getting them used to outdoor conditions like wind, sun, and changing temperatures. Start this process about ten to fourteen days before you plan to transplant them into your garden.
On the first day, place the seedlings outside in a shaded, sheltered spot for one to two hours, then bring them back inside. Each day, increase their time outdoors and gradually expose them to more sunlight. Always bring them indoors at night unless the temperatures are very mild. This slow transition toughens up your seedlings and helps prevent transplant shock, giving them the best chance to thrive when they go into the ground.
Step 7: When Are Seedlings Ready to Go Outside?
Before moving your seedlings to your outdoor garden beds, it’s important to make sure they’re mature and sturdy enough to handle the transition. A good rule of thumb is to wait until your seedlings have at least two to three sets of “true leaves”—the ones that grow after the first small seed leaves (called cotyledons). At this point, the plant is photosynthesizing and growing on its own.
Your seedlings should be about 3 to 6 inches tall, with strong, thick stems. If they are tall and wobbly, they may need more time under the grow lights or better airflow to strengthen their stems. The roots should be well-developed and hold the soil together when gently removed from the container. If the roots are still fragile or fall apart easily, give your seedlings more time indoors. However, if the roots are circling the pot tightly (called rootbound), it’s time to transplant.
Step 8: Planting Dates
Depending on where you live, the growing season can be limited, and it can be challenging to extend it. Know which crops are cold tolerant and which need warmth to thrive. Know how to protect your seeds and seedlings from unexpected temperatures. Learn more details about planting dates in the Chicago area in our blog post on planting calendar for Zones 5b & 6a.
The average last frost dates for Chicago and its surrounding suburbs, including Oak Park and River Forest, in 2025 are typically April 21 to 30. However, it's important to note that this is just an average, and there's always a chance of frost occurring before or after these dates.
Gardeners not in the Chicago area can ask their local university ag extension or a botanic garden for a planting calendar and average frost dates for their climate zone.
Final Thoughts
Starting seeds indoors is a simple and deeply rewarding practice that lets you take control of your growing season. It’s a fun way to engage with your garden long before outdoor planting begins. With a little planning, care, and patience, you’ll grow strong, healthy transplants that are ready to flourish the moment they hit the soil.
You can also use Winter Sowing techniques to start some seeds outdoors - see the blog linked below.
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Beautify Your Garden with Our Cedar Raised Beds!
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Deep Roots Supports Gardeners
We provide our gardeners with the best products for success – like cedar raised beds, microbe-rich compost and microbe-rich worm castings. Check our online store. Always talk to our customer support team before placing your order online. If you need help or have a question contact us at support[at]deep-roots-project.org and 708-655-5299.
Deep Roots Online Store
See our online store for details about prices, ordering and delivery of raised beds, planter boxes, microbe-rich compost, worm castings, leaf mulch and more. We don’t sell traditional soil, since we use 100% compost as our growing medium. Our online store has 2 sections – (1) raised beds and planter boxes and (2) compost, worm castings, fertilizer.
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