How to Plant Seeds in a Basic Seed Tray

Starting plants from seeds is an excellent way to prepare your garden indoors. Seed trays make the process simple and efficient, allowing your plants to develop strong roots with minimal work. By preparing your seeds ahead of spring, you’ll have healthy seedlings ready to be transplanted outdoors in no time.

Creating a Grow Area

Begin planting your seeds about 6–12 weeks before the last expected frost in your area. The exact timing will vary depending on the type of plants you’re growing. Using the local frost date as a reference helps you determine the best time to start germination.
Be sure to read the seed packet for any special instructions, such as soaking or chilling, that may be required before planting.
For region-specific planting dates, consult resources like The Old Farmer’s Almanac.

Choose a cell tray with drainage holes for a convenient and efficient way to start your seeds. These trays allow each seed to grow in its own space, preventing roots from tangling. Whenever possible, select trays with built-in drainage holes to ensure proper water flow. You can find them at most gardening supply stores.
If your tray doesn’t come with drainage holes, simply use a knife to carefully poke a few at the bottom of each cell.

Create a DIY seed tray using a cardboard egg carton as a budget-friendly, eco-friendly alternative. The individual compartments are perfectly sized for planting seeds, and you might already have one available at home. Once the eggs are gone, poke a few small holes in the bottom of each section to allow for proper soil drainage.

Set your cell tray inside a large, flat plastic tray to make watering and moving your seedlings easier. This setup encourages the roots to grow downward, as water will be absorbed from the bottom. You can find plastic trays at most gardening stores, or use a baking pan you already have at home as a convenient alternative.

Fill each cell to the top with a seed-starting mix. This sterile, lightweight medium is specially designed to encourage fast and healthy germination and is available at most garden centers or online. Don’t worry about slightly overfilling—the mix will settle once it’s moistened.
While potting soil can be used as an alternative, it’s usually coarser in texture and may not support seed growth as effectively as a fine seed-starting mix.

Moisten the seed-starting mix using a watering can until it feels evenly damp. Check by pressing your finger into the soil up to your first knuckle—if it feels moist but not soggy, it’s perfect. Any excess water should drain into the tray beneath the cells, ensuring the soil stays hydrated without becoming waterlogged.

Sowing the Seeds

Test the viability of old seeds by soaking them in water for 15 minutes. This helps determine whether they are still good for planting. While some seeds remain viable for years, others may lose their ability to germinate sooner. Seeds that float are unlikely to grow, whereas those that sink are generally still viable.

Alternatively, you can perform a germination test: place at least 10 seeds in a damp paper towel, seal it in a plastic bag, and keep it in a warm location for 10 days. If at least half of the seeds sprout, the remaining seeds should be viable for planting.

Use your finger to create a small hole about ¼ inch (6.4 mm) deep in each cell—roughly half the length of a fingernail. Press gently to avoid compacting the soil.
Keep in mind that some seeds may require shallower or deeper planting, so always follow the specific instructions on the seed packet for best results.

Place at least two seeds in each hole to increase the chances that at least one will germinate. If both seeds sprout, you can later thin them by removing the weaker seedling.

For very small seeds, plant four per hole to improve the odds of successful growth. To handle tiny seeds more easily, pour them into the crease of a folded piece of paper and use a pencil to gently drop them into the planting hole.

Lightly cover the seeds with seed-starting mix and gently press down with your finger to ensure full contact between the seed and the soil. Press softly—your goal is to firm the soil around the seed, not to push it deeper.

If you’re planting multiple types of seeds, be sure to label each variety. Create garden labels that note both the plant type and the planting date, and place them at the end of each row.

A simple DIY alternative is to use toothpicks and masking tape to make your own labels at home.

Caring for Your Seedlings

Cover the tray with plastic wrap to retain moisture and create a humid environment that encourages seed germination. Leave small gaps along the sides to allow air circulation.

Alternatively, you can use a humidity dome from a gardening store. If the dome includes an air vent, keep it slightly open to ensure proper airflow.

Pour about ½ inch (13 mm) of distilled water into the flat tray. The cells will absorb water from the bottom, eliminating the need to water from above. Check the water level daily.

Refill the tray to ½ inch (13 mm) whenever it drops below 1⁄8 inch (3.2 mm). Avoid overfilling, as excess water can waterlog the seedlings’ roots and cause rot.

Keep the plant seeding tray in a warm location. While direct sunlight isn’t necessary for seeds to germinate, it won’t harm them either. Aim to maintain the soil temperature above 65 °F (18 °C), as this supports successful germination for most plants.

You can monitor the temperature using a soil thermometer placed at the same depth as the seeds.

Once your seedlings emerge, move the tray to a bright area, such as a windowsill, where they can receive around six hours of indirect sunlight. Remove the plastic wrap or humidity cover to allow full light exposure.

To prevent the seedlings from leaning or growing unevenly, rotate the tray 180° every other day. Alternatively, you can use grow lights to ensure even growth.