Starting your own plants from seed is one of the most rewarding and cost-effective ways to grow a garden. Whether you're planting vegetables, herbs, or flowers, learning how to start seeds indoors will give your plants a strong head start before they transition to the outdoors. By starting seeds indoors, you can extend your growing season, control the conditions your plants grow in, and enjoy a wider variety of crops that might not be available as young plants at garden centres.
This guide will walk you through everything you need to know about indoor seed starting, from choosing the right seeds to ensuring your seedlings grow into healthy, thriving plants.
Why Start Seeds Indoors?
Starting seeds indoors provides several advantages for home gardeners. Firstly, it enables you to initiate the growing season early, guaranteeing a strong foundation for your plants before they transition outdoors. By the time the last frost has passed, your seedlings will be strong and ready to thrive in your garden.
Another benefit of starting seeds indoors is that it saves money. A single packet of seeds costs significantly less than buying fully grown plants, and with proper care, one packet can yield dozens of seedlings. Additionally, growing from seed allows you to choose from a wider selection of plant varieties, including heirloom and specialty plants that may not be available as seedlings in stores.
Lastly, by controlling the environment, you can ensure that your plants grow in optimal conditions. Seedlings started indoors are often healthier and more resilient than those grown in less controlled outdoor conditions.
What You’ll Need to Start Seeds Indoors
To start seeds successfully indoors, you’ll need the right supplies. Begin by selecting high-quality seeds suited to your climate and garden. Some of the best vegetables to start indoors include tomatoes, peppers, eggplants, broccoli, and lettuce. Flowers such as marigolds, petunias, zinnias, and snapdragons also grow well from seed. Herbs like basil, parsley, oregano, and thyme are excellent choices as well.
Next, gather seed trays or small containers for planting. You can use specialized seed-starting trays, small pots, or even repurposed items like egg cartons. Fill these containers with a light, well-draining seed-starting mix rather than regular garden soil, which can be too heavy for delicate seedlings.
Providing adequate light is essential for seedling growth. If you have a sunny, south-facing window, that may be enough, but most seedlings require 12-16 hours of bright light daily. Grow lights are a great investment to ensure strong, healthy plants. You’ll also need a spray bottle or watering tray to keep the soil evenly moist and humidity domes or plastic wrap to retain moisture during germination. Finally, label your trays to keep track of what you planted.
Step-by-Step Guide to Starting Seeds Indoors
1. Choose the Right Seeds for Indoor Starting
Not all seeds need to be started indoors. Some plants, like carrots, beets, and peas, grow best when directly sown outdoors. However, crops that require a longer growing season, such as tomatoes, peppers, and eggplants, benefit from being started indoors.
2. Prepare Your Seed Trays and Soil
Before planting, make sure your seed trays or containers are clean to prevent disease. Fill each container with a moist seed-starting mix, ensuring that it is neither too dry nor too soggy. Lightly press the soil down but avoid compacting it, as this can inhibit root growth.
3. Plant the Seeds at the Right Depth
Each seed has a recommended planting depth, which is usually indicated on the seed packet. Generally, you should plant seeds twice as deep as their size. For example, tiny seeds like basil should be placed on the surface and lightly covered with soil, while larger seeds like tomatoes should be planted about ¼ inch deep. After planting, gently mist the soil with water.
4. Provide Adequate Light for Seedlings
Seedlings require plenty of bright light to grow strong and healthy. If you are using grow lights, keep them 2-4 inches above the plants and adjust them as the seedlings grow. Without enough light, seedlings may become leggy and weak, making them more susceptible to disease and poor growth.
5. Maintain Proper Moisture and Humidity
Water is crucial for seed germination, but overwatering can be harmful. Keep the soil evenly moist but not soaking wet. Using a spray bottle or bottom-watering method helps prevent overwatering. Covering the trays with a humidity dome or plastic wrap can help retain moisture during the early stages of germination. Once the seeds sprout, remove the cover to prevent mold and allow air circulation.
6. Keep Seeds at the Right Temperature for Germination
Most seeds germinate best in temperatures between 65-75°F (18-24°C). Some seeds, such as peppers and tomatoes, benefit from additional warmth and may germinate faster with the use of a heat mat. Once the seedlings emerge, they can be moved to a slightly cooler location, ideally between 60-70°F (15-21°C).
7. Thin Out Weak Seedlings
Once your seedlings begin growing, you may notice multiple sprouts per cell. To prevent overcrowding, thin them out by snipping the weaker seedlings at the base, leaving only the strongest plant. This ensures that the remaining seedlings receive enough nutrients, light, and space to develop properly.
8. Start Fertilizing After the First True Leaves Appear
After seedlings develop their second set of leaves, known as true leaves, they require additional nutrients. Begin feeding them with a diluted liquid fertilizer at one-quarter strength every one to two weeks to support healthy growth.
9. Transplant Seedlings When They Outgrow Their Containers
If your seedlings start to outgrow their trays before they are ready to be planted outdoors, transfer them to larger pots to give them more space to develop strong roots.
10. Harden Off Seedlings Before Planting Outdoors
Before transplanting seedlings into your garden, they need to be gradually introduced to outdoor conditions. About a week before planting, start placing your seedlings outside in a sheltered location for a few hours each day. Gradually increase their exposure to sunlight and outdoor temperatures while bringing them indoors at night. This process, known as hardening off, helps prevent transplant shock and prepares the seedlings for life in the garden.
Common Mistakes to Avoid
One of the biggest mistakes new gardeners make is overwatering their seedlings. Too much water can cause damping-off disease, a fungal condition that kills young plants. Additionally, insufficient light is a common issue that results in weak, leggy seedlings.
Another mistake is skipping the hardening-off process before moving plants outdoors. Sudden exposure to sun and wind can shock young plants, causing them to wilt or struggle to adapt. Lastly, failing to thin seedlings properly can lead to overcrowded plants that compete for nutrients, leading to stunted growth.
Final Thoughts
Starting seeds indoors is a fun and rewarding way to take control of your garden and ensure a successful growing season. By choosing the right seeds, providing proper lighting and moisture, and following good planting practices, you can grow strong, healthy plants that will thrive when moved outdoors.
Whether you're growing vegetables, flowers, or herbs, taking the time to start seeds indoors will give you a significant advantage. Visit your local garden centre to pick up supplies and get started today.