How To Start Plants From Seed

Starting plants from seed can be a rewarding and cost-effective way to grow a diverse variety of plants for your garden. This method allows you to choose from a wider selection of plant varieties and harvest your crops earlier than if you were to plant seedlings. Here, This Old House landscape contractor Roger Cook shares expert tips and techniques for successfully starting plants from seed.

*Unless otherwise noted, costs in this article reflect an average of prices that our team found from hardware stores like Lowes and Home Depot, and on Amazon.com.

Benefits of Starting Plants from Seed

Starting plants from seed offers several advantages over purchasing seedlings from a garden center:

• Cost-effectiveness: Seed packets are significantly cheaper than potted seedlings, allowing you to grow more plants for less money—one packet of seeds often only costs $1–$5.
• Earlier harvest: By starting seeds indoors, you can harvest your plants weeks earlier than if you planted seedlings outdoors.
• Greater variety: Seed catalogs offer a much wider selection of plant varieties than what’s typically available as seedlings at garden centers.

Beyond cost and variety, seed-grown plants can actually be more vigorous than store-bought transplants. As This Old House Magazine notes, starting with seeds “often results in more robust plants, since there’s no risk of damaging fragile root hairs during transplanting.” Many experienced gardeners use a hybrid approach — starting heat-loving crops like tomatoes and peppers from transplants while planting most other varieties from seed. Root vegetables, such as carrots, don’t transplant well, so they are best started from seed.

Choosing Containers for Seed Starting

Selecting the right container can influence the success rate of your seeds, and you have several options. Recycled containers are economical and environmentally friendly. Biodegradable pots help reduce transplant shock and can be directly planted into the soil. Divided-cell trays offer organized planting, while open-style trays allow for mass planting of seeds. Each type of container has its benefits, so consider what works best for your gardening needs.

• Recycled containers: Almost any container can be repurposed for seed starting, such as milk cartons or plastic tubs. Just be sure to punch drainage holes in the bottom.
• Biodegradable pots: These can be planted directly in the garden without removing the seedlings.
• Divided-cell trays: These have individual compartments for each seed, making it easier to separate seedlings when it’s time to transplant.
• Open-style trays: These allow you to plant more seeds in a single container, but may make it more challenging to separate seedlings later.

Pro Tip: Roger Cook, This Old House landscape contractor, recommends using plastic cell packs over decorative pottery for seed starting: “I want as sterile an environment as I can get.” He advises filling the six-packs with soilless mix, pushing it down firmly, then adding more and leveling it off to the top. The key distinction: you want the mix firm, not tight.

If you’re reusing containers from previous seasons, take care to avoid exposing seedlings to pathogens. Clean used containers with hot, soapy water before filling them, and opt for a sterile soilless mix rather than garden soil. As noted in This Old House Magazine, seeds will germinate in any container with drainage — from peat pots to plastic cell packs or even yogurt cups with holes punched in the bottoms.

Preparing the Soil Mix for Your Seeds

The right soil mix is important for successful seed starting, and preparing the soil mix correctly ensures that seedlings have the best possible start. The lightweight and free-draining nature of the sphagnum moss and vermiculite mixture provides the ideal growing environment for young roots. Here’s how to prepare it:

1. Use a mixture: Combine sphagnum moss and vermiculite instead of garden soil, which is too heavy for seedlings.
2. Blend well: Ensure the mixture is even by thoroughly combining the sphagnum moss and vermiculite in a small plastic bucket.
3. Hydrate the mix: Add water to the mixture and blend thoroughly with a garden trowel.
4. Fill containers: Once hydrated, fill your chosen containers with the soil mix.

Planting the Seeds

Proper planting techniques are essential for good germination rates, so you need to ensure that the seeds are at the right depth and have good contact with the soil. Follow these steps to plant your seeds:

1. Create planting holes: Make a hole in the soil that is two to three times the size of the seed.
2. Place seeds: Drop the seed into the hole and cover it with soil.
3. Ensure contact: Gently press down on the soil to ensure good contact between the seed and the growing medium.
4. Plant in trenches: For open-style trays, create shallow trenches, sprinkle in the seeds, cover with soil, and press down.

Pro Tip: Use a sterile soilless mix of sphagnum moss and vermiculite rather than garden soil from your yard. As demonstrated on Ask This Old House, garden soil is too heavy for delicate seedlings to push through, while a sphagnum-and-vermiculite blend provides the spongy, free-draining environment that seeds need to germinate and grow strong roots.

Seed Watering and Maintaining Moisture

Maintaining the right moisture level is just as important for seed germination as proper planting. Too much or too little water can hinder the process, so regular monitoring is key. Here are some tips for proper watering:

1. Use a mister: A light mister helps to water the soil surface gently, avoiding washing away the seeds.
2. Wick up water: Place water in a solid tray without drainage holes and set the planted tray inside to allow water to wick up from the bottom.
3. Cover the tray: To maintain moisture and prevent evaporation, cover the tray with a clear plastic dome.

Providing Heat and Light for Your Plants

You’ll need adequate heat and light to keep your seedlings sprouting strong, since seeds require warmth to germinate and light once they sprout. The right conditions can significantly influence the success rate of your seedlings—warmth triggers germination, and sufficient light ensures sturdy, healthy growth. Here are some ways to optimize heat and light for your seeds:

• Use a heating pad: Place the seed tray on an electric heating pad to encourage germination.
• Move to a light source: Once seedlings emerge, move the tray to a sunny window or under grow lights.
• Adjust grow lights: If using grow lights, position them close to the tray and raise them as the plants grow taller.
• Provide adequate light: Ensure seedlings receive 14 to 16 hours of light per day for optimal growth.

Hardening Off and Transplanting Seeds

Hardening off helps seedlings adjust to the harsh conditions of outdoor life. It’s an important step for ensuring their survival and continued growth. Before moving your seedlings outdoors, they need to be gradually acclimated to outdoor conditions:

1. Wait for the right time: Wait at least a week after the last frost date in your region before transplanting.
2. Start hardening off: Begin the hardening-off process by placing the seedling tray outdoors for two to three hours, then bringing it back inside.
3. Gradually increase exposure: Repeat this process for several days, slowly increasing the seedlings’ exposure to outdoor conditions.
4. Transplant carefully: When ready to transplant, gently remove the seedlings from their containers and plant them in your garden.

Pro Tip: Roger Cook, This Old House landscape contractor, explains the importance of timing: “You need to know the date of the last frost in your region because if we put these outside and there was a frost, the chances are they’d all be killed. So, obviously, go beyond the last frost. How far beyond? I would say at least a week, if not two.”

Common Challenges and Solutions When Starting Plants From Seed

Starting plants from seed can present some challenges—knowing how to identify and address common problems can make your seed-starting efforts more successful. Stay vigilant and adjust care practices as needed to mitigate any issues. Here are some common issues and how to address them:

• Damping off: This fungal disease can kill seedlings. Prevent it by using sterile soil and containers, providing good air circulation, and avoiding overwatering.
• Leggy seedlings: Insufficient light causes seedlings to stretch. Ensure they receive adequate light and rotate trays regularly for even growth.
• Uneven germination: Some seeds may sprout faster than others. Be patient and provide consistent moisture and warmth for best results.

Our Conclusion

Starting plants from seed is an economical and rewarding way to grow a diverse garden. With the right techniques, materials, and care, you can successfully nurture seedlings into healthy, productive plants. By following these steps and tips from Roger Cook, you’ll be well on your way to enjoying a bountiful harvest from your homegrown plants.