7 Indoor Seed-Starting Tips for Faster Germination and Healthier Plants

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Key Takeaways

Before starting seeds, familiarize yourself with all the specific requirements of each seed.
Plant seeds at the right depth in pre-moistened soilless seed-starting mix.
Water regularly so the growth medium never dries out during the germination process.

Seeds need the right conditions to break out of their protective seed coat. Coaxing those green shoots to sprout depends on the type of seed's temperature, light, and moisture requirements. If conditions are not spot-on, seeds will languish in the soil for weeks or may not germinate at all. Here's how to create the optimal environment for seed-starting, plus straightforward tips for increasing your germination success.

1. Study the Seed Packet

The most valuable information about how to germinate a particular seed is usually found on the seed packet. These info-packed envelopes include sowing depth, days to germination, special preparation techniques (from soaking seeds to nicking the coat), and light and water needs. Before starting seeds, carefully read the seed packet.

If you don't have a seed packet because you were given seeds by a friend or neighbor, search for it online. The websites of seed companies and Extension Services provide reliable information for seed starting.

Take a photo of the seed packet with your phone. The photo will be a handy reference for transplanting seedlings and plant spacing in the garden.

2. Sow at the Right Depth

How deeply a seed is buried impacts germination. Follow the planting depth recommendation on the seed packet. As a general rule, the larger the seed, the deeper the planting depth. Planting a seed deeper than recommended can delay or even prevent germination.

Watering newly sowed seeds with a watering can from above can disturb the soil enough to cause the planting depth to become too deep or shallow. To ensure seeds remain at the proper depth, water from below. Set the pot or seed-starting tray in a shallow tray of water for 30 minutes or so.

3. Prep the Growth Medium

For best results, use a soilless seed starting mix designed to provide the ideal environment to germinate seeds and promote strong root development of the seedlings. Before filling your containers, thoroughly moisten the dry mix by slowly adding water and incorporating it as you go. A properly moistened mix should have the consistency of a wrung-out sponge.

When filling pots or seed trays with the seed starting mix, stop ½ to 1 inch below the top of the vessel. The extra space will prevent soil from spilling over the top of the pot or tray when watering the seedlings.

4. Treat the Seed Coat If Needed

Some seeds need a helping hand to break through their tough seed coat. Morning glory and sweet pea seeds, for example, germinate best when nicked with a nail clipper, just enough to break the seed coat so moisture can enter more easily. If the seed packet suggests a seed treatment before planting, take the extra time to perform the treatment. You’ll be rewarded with speedier germination.

Some seeds need a cold period called stratification to germinate. A few weeks in the refrigerator will usually get the job done.

5. Add Heat If Needed

Many seeds will germinate at average room temperature, but some seeds require consistent warm soil temperatures between 70°F and 75°F around the clock. Immediately after sowing seeds, place containers on a seedling heat mat or, as a no-cost alternative, on top of a refrigerator or near a radiator. After the seeds have germinated, remove the seedlings from the heat source. They grow best when day and night temperatures fluctuate by a few degrees.

6. Provide Plenty of Light

Some seeds, such as tomato seeds, germinate under the soil in darkness, whereas others, such as coleus, need light to germinate. The seed packet will provide light details. Seeds that require light to germinate are scattered on top of the growth medium or lightly pressed into it, but not covered. If light is not explicitly mentioned but planting depth is detailed, you can safely assume the seed germinates in darkness.

After the seeds germinate, all seedlings need 12 to 16 hours of bright light every day. Use a grow light to supplement any natural light your indoor space gets.

7. Water Well

Sufficient moisture is critical at all stages of germination. It's especially critical once the germination process has started; if the seeds dry out once they've sprouted, even for a few hours, they usually don't recover. The opposite, overwatering, is also detrimental because the seeds may rot.

Plant seeds in moist but not soggy growth medium. Then mist the soil surface with water from a spray bottle, never a watering can. Cover the pot or seed tray with plastic wrap or a humidity dome. As soon as the seeds germinate, remove the covering to encourage air circulation and prevent mold. Getting moisture levels just right gets easier with practice.