9 Tips for Better Seed Germination Rates This Season

If you’re tired of planting seeds that never seem to germinate, you’ll be glad to know that a few simple fixes could revolutionize your seed-starting process. Many gardeners make simple seed starting mistakes that can be avoided if you plan ahead.

Poor seed germination can cost you time, effort, and money, ultimately setting back your spring gardening efforts by weeks or even months. The best way to boost germination is to optimize the 3 factors for successful seed germination:

1. Temperature
2. Moisture
3. Light

Let’s dig into how you can perfect these conditions using science-backed tips for better seed germination!

Don’t Let Your Soil Dry Out

Both dry soil and soggy soil are among the quickest killers of germinating seeds. These opposite ends of the moisture spectrum can be catastrophic for seeds of all types, but especially for vegetable seeds that are germinating in seedling trays:

• Too little water can halt the germination process.
• This will cause the seeds to shrivel and die.
• Too much water can lead to seed rotting.
• It can also lead to compacted soil, hypoxic (low oxygen) conditions, and damping off disease.

Seeds are robust enough to fly through the wind and stay stored in containers all winter long. But once they break dormancy and start germinating, seeds become as needy as a newborn baby. They need a constant source of moisture because they haven’t developed a root system to scavenge the soil for water. Remember:

• Dry seeds hibernate
• Moist seeds germinate
• Soggy seeds rot

Maintain continuous soil moisture by monitoring your seeds on a daily basis. Some seeds can last a few hours to a day without sufficient moisture, but it’s best to prevent this stress. Water stress can cause stunting and poor plant vigor down the road. Check your babies regularly!

For indoor seed starting, check both the surface soil and the soil near the drainage hole of the seedling tray. If it looks dull or dry, it’s time to water. When irrigating, water your trays until water pours through the bottom holes, then stop.

Provide Enough Light

While the initial germination process happens in the darkness of soil, all plants need light once they reach the surface. If your seedlings aren’t getting enough sunlight or artificial light, they are unlikely to succeed. Weak, leggy, or spindly baby plants are most often the result of low-light conditions.

For better seed germination indoors, consider investing in a supplemental lighting setup or a mini nursery greenhouse. You can also place seed-starting containers as close as possible to a bright, south-facing window.

Outdoor seeds should be sown in an area that isn’t shaded out by plants or structures. The sunlight will do the work for you as long as deep mulch or shadows don’t get in the way.

Use a Soil Thermometer

Soil thermometers are the most underrated tools for seed starting. When it comes to germination, the ambient (air) temperature is not nearly as important as the soil temperature. Seeds respond to specific underground conditions that determine their germination rates (how many seeds come up) and germination speed (how long it takes).

Invest in a quality soil thermometer and use it to monitor the soil temperature of both seedling trays and outdoor garden beds. Because soil is naturally “insulated”, it is naturally buffered against extreme temperature fluctuations. This means that a drastic change in weather won’t change the soil temperature as quickly.

Instead of planning your seeding dates based on weather, start to seed when the soil temperature is in the right range. 

Soil Temperature Cheat Sheet

This cheat sheet was adapted from reputable scientific research at the University of California. These numbers don’t necessarily mean that your seeds won’t germinate at higher or lower temperatures, but the optimum range is shown to produce the most consistent germination results. A soil probe thermometer is the most reliable way to gauge your seeds’ chance at success.

Use a Heating Mat

If you don’t have the ability to create a fully climate-controlled greenhouse, a heating mat is the easiest (and cheapest) way to skyrocket your germination rates for warm-weather crops like tomatoes, peppers, cucumbers, and squash.

These waterproof electric mats are easy to arrange beneath seed-starting trays and set to a specific temperature. Simply plug it in, set your trays on top, and watch the magic happen!

Some seeds (like brassicas) prefer a heating mat only during the germination period and should be removed from the mat after they germinate. Others (squash, tomatoes, peppers, etc.) can rest on the heating mat throughout their early seedling growth stage.

Sow at the Proper Depth

Just like a baby needs to be swaddled beneath and the perfect number of blankets to stay cozy, seeds need to be tucked in at a certain depth to germinate properly. On one hand, you don’t want to smother your seeds with a super thick blanket of soil. If you plant too deep, the seeds may not have enough energy to reach the light.

On the other hand, seeds without the proper covering are left bare and exposed to the elements. If you plant too shallow, the seeds could blow away, dry out, or get dislodged during watering.

General Rule of Thumb: Sow seeds twice as deep as their size.

• Large seeds like squash and beans can be sown up to an inch deep in the soil.
• Medium seeds like tomatoes or brassicas can be planted in a small hole about twice their size.
• Tiny seeds like lettuce and basil should be sprinkled with a thin layer of soil over the top.

Use a Well-drained Soil Mix

Drainage is crucial for happy germination because it prevents seeds from rotting in the soil. Water can move more quickly through the seedling tray. Additionally, well-drained soil has extra oxygen between the particles to help the seeds “breathe.” If you are experiencing uneven germination, it may be because your seeds are suffocating inside heavy or poorly drained soil.

Look for a soil mix that is specially formulated for seeds. These blends will be different from potting mix or garden bed mix because they have extra drainage that is ideal for container growing.

The best ingredients of a well-drained seedling mix include:

• Sieved compost
• Perlite
• Vermiculite
• Coco coir
• Peat moss
• Vermicompost

When growing in trays, avoid reusing old soil mix or pulling soil from the garden. This helps prevent damping off, which is a nasty seedling disease caused by a soil fungus that thrives in moist environments.

If direct sowing outdoors, be sure you’ve prepared a well-drained seed bed. Consider integrating sieved compost, peat moss, coco coir, or perlite into the soil. You can use a tilther (a shallow tiller), a scuffle hoe, or a shovel to break up large clumps of soil.

Then, rake the soil smooth before seeding. If your soil is heavy or high in clay, you can pour a thin layer of seed-starting mix over the garden bed and seed into that.

Don’t Plant Old Seeds

Some seeds can last for years or even decades of dormancy, but these are rare outliers! Generally, the older a seed gets, the less likely it is to germinate. Vegetable seeds reward you with the quickest, most even germination when they are young.

Seed companies document a seed’s age with a lot number and date listed on the seed package. Before planting, check the dates on your seed packets and make sure they are only 1-2 years old.

Throw away seeds that are more than 3-5 years old. For hybrid seeds, it is best to re-order new seeds every year.

Use Row Cover for Direct Sown Seeds

When you are direct seeding in the garden, it is more difficult to maintain consistent conditions amidst outdoor weather changes. Row cover is an agricultural fabric that allows light and water to pass through it, which creates a more easygoing environment for seeds.

This fabric can dramatically improve germination success because it creates a “microclimate” of cozy warmth beneath it. Moreover, it helps retain consistent moisture by buffering the seeds against the harsh drying effects of wind.

Better yet, row cover protects germinating seeds from pests! Instead of relying on pesticides or biocontrol, row cover physically prevents pests from reaching newly germinate seeds. For example, crops like radishes, turnips, and arugula are particularly prone to flea beetles.

When they are protected by row fabric during germination, these vegetables can thrive without any of the nasty impacts of flea beetles on their leaves. Professional growers swear by this!

Use row cover over outdoor seeds to retain moisture and moderate the temperature. Purchase a row fabric thickness that is optimized to your crops and climate.

Thicker fabric allows less light but provides more warmth for germinating carrots, cucumbers, or greens. Thinner row fabric is best for pest exclusion in cold-loving crops like spinach.

Place row fabric directly over the soil surface after seeding. Secure with landscape staples, bricks, sandbags, or other weights along the perimeter to prevent the fabric from blowing away.

Don’t Sow Too Densely

It’s normal to plant extra seeds to ensure you have enough plants for the season. However, if you forget to thin your seedlings, they can quickly become overcrowded and prone to diseases. Dense sowing can also cause your plants to be stunted, weak, or spindly in their growth.

When growing in seed trays, plant just 2-3 seeds per cell. Most vegetables can be thinned to one seedling per cell. When growing outdoors, you will need to check the recommended spacing for the specific variety. If the seeds are very small, use a hand seeder to prevent dumping too many seeds in one area.

The best time to thin is when seedlings develop their first sets of true leaves. Use needle-nose pruners or thin scissors to cut the undesired seedlings at the base. Do not pull or yank seedlings out because this can disturb the roots of the plants you want to keep.