Tips To Improve Seed Germination Outdoors

Sowing seeds directly into the soil and letting nature do the rest. It’s simple, and uncomplicated. Many of us learned to garden this way as children, sowing seeds with our grubby little fingers. We tucked seeds into the ground, forgot about them after a day or two, and then came back to see amazing little green sprouts pop up in rows. 

I start hundreds of seedlings indoors every year, but I directly sow as much as I can right into my garden beds for simplicity and speed. A few dozen lettuce seeds can be tucked into an open space in a minute or two. Sometimes, I’ll plant just before a rain shower so I don’t even need to water them.

Although planting seeds directly in the garden is intuitive, paying attention to timing, moisture, and soil temperature will improve your seed germination rates when sowing outdoors.

Seed Viability and Soil Preparation for Outdoor Sowing

Starting with good quality, viable seed is essential. While many seeds last for years in perfect conditions, our homes aren't usually designed for long-term seed storage. Look at the packet and check the date. Often, it is listed as "packaged for" and a year. That's the year the seed is freshest. 

For example, "packaged for 2023" would indicate that the seed was likely harvested at the end of the 2022 season and should be planted in 2023 for the best germination results. In 2024, germination will likely still be good but slightly lower than the year before. A seed's ability to germinate, or viability, decreases over time, even when stored perfectly. Eventually, the seed becomes non-viable and won't sprout. You can learn how to check seed viability and germination rates here. 

Most vegetable seeds, stored in a cool and dry location, will last at least three years. However, it varies widely by species. Check this table compiled by the University of Nebraska-Lincoln Extension for a guide on how long commonly grown seeds can be stored.

Preparing the soil is a key step in the successful outdoor seed-starting journey. As you can imagine, hard, stony, compacted, or poor soil isn't conducive to sprouting seeds. While it's true that in nature, seeds sprout without humans fussing over them, the success rates are lower than we would like for our gardens. In the forest, one acorn in ten thousand grows into an oak tree. In our garden, we'd like to do better.

To prepare a proper outdoor seedbed:

• Loosen the soil with a garden fork, and remove all weeds and rocks.
• Work in a layer of compost or aged manure—the seeds don’t need it, but the mature plants will, and you won’t get a chance to add it later because the plants will be there!
• Smooth out the surface with a rake or, for small spots, your hand. A smooth surface is easier to plant seeds on.
• Prepare row markers. It's easy to forget where you planted seeds, especially after a few days. 

When to Plant Seeds Outdoors

Many new gardeners make the mistake of planting too early, whether seeds or young plants. Just as young plants can be set out too early and suffer from cold temperatures and harsh weather, seeds can be planted too early. 

Timing for sowing seeds in the ground largely depends upon the soil's warmth. Inside each seed is a dormant embryo waiting for the right signals to wake up and grow. Moisture and temperature are two important factors. Planting too early can mean cold soil temperatures that won't be sufficient to wake up your seeds, leading to them eventually rotting in the ground. 

Some seeds, like lettuces, will germinate in cool soils, and others won't sprout until the soil warms up quite a bit, like melons and squash. Generally, cool-season vegetables or flowers will germinate in cooler soil temps—which makes sense. Heat-of-the-summer kinds of plants, like watermelons, want warmer soil to germinate. Think of it like a defense mechanism against frosts. If you're a plant that can't handle any frost, you probably don't want to germinate when soil temps are still in the 40s and nights are dipping below freezing.

I don't use a soil thermometer, and your grandparents probably didn't either. When directly sowing, I split the seeds into warm and cool categories. Then, I use a very scientific method to determine if the soil is at the right temperature—I feel it.

If the soil feels icy, or I see ice crystals, it's too cold to plant (winter sowing and stratification notwithstanding). If the soil feels cool to the touch in the top inch, where seeds get planted, it's ready for those early, cool-season crops. If it feels neutral to slightly warm in my hand, it's ready for warm-season crops like okra and cucumbers. Of course, you'll also want to monitor the weather forecast. 

Frost Dates

Seed packets for cool-weather crops often state that they can be directly sown "as soon as soil can be worked." When is that? 

The ground can be worked when the frost has thawed from the soil and drainage is restored (ponding water is no longer on the surface). For most folks, that happens about 4–6 weeks before their last frost date in spring. So, you could be planting lettuce, pea, and radish seeds outside a month before your last frost date. Seed packets for warm-weather plants often simply state that they should be planted outside after the last frost.

How Deep to Plant Seeds 

The seed package usually states the depth at which to plant seeds. While seed depth is important, you don't need to use a machinist's rule to measure it. While some folks like to go by the rule of "two times as deep as the seed is wide," I just follow the directions on the package. 

When the package directions state:

• Plant ⅛" deep: Barely cover the seeds with soil. 
• Plant ¼" deep: Use your fingertip to draw a shallow trench in the soil, lay out the seeds in the trench, and cover them with a layer of soil about the thickness of a pencil.
• Plant ½" deep: Use your finger to make a slightly deeper trench, or, as I do, poke a hole about as deep as your fingernail, drop the seed in, and cover it up.
• Plant 1" deep: Poke a hole as deep as the first knuckle of your index finger. Drop the seed in and cover with soil.

In all cases, lightly pat or firm the soil after planting so the seed is pressed against the soil. Good seed-to-soil contact is important for germination. 

Watering Seeds After Planting Outdoors

Moisture is necessary for seeds to germinate (along with oxygen and warmth). As moisture is absorbed by the seed, it swells, and the hard seed coating splits. Enzymes and stored food become hydrated, the cells swell with water, and metabolic processes begin. Pretty cool, right? In soil that's too dry, all that neat biology stuff doesn't happen, and your seeds won't sprout. 

However, too much moisture means soggy, wet, anaerobic conditions with low oxygen levels. That won't work either. The seeds rot without ever waking up. We must achieve balance.

Unless the soil is already fairly damp, gently water seeds in after planting. Check if you watered deeply enough by sticking your finger into the soil about the depth you planted. Take care to water gently—a vigorous splashing can wash the soil right off the seeds and your seeds right out of their new homes. 

Monitoring soil moisture is essential when seeds are germinating and when seedlings have just emerged. Keep the soil slightly damp to the touch, but not muddy. The top inch of soil can dry quickly in hot sunshine, dehydrating tender seedlings.

Critter Problems When Germinating Seeds Outdoors

One vexing issue that gardeners face when directly sowing seeds outdoors is competition from animals. All winter long, my birdfeeder is full of treats for songbirds. Then, in spring, they think I've decided to scatter their treats in the garden, and they go looking for them! 

While I can't explain exactly why these tactics work, they do for me. If you have issues with birds or chipmunks snagging your freshly-sown seeds for their lunch, give these a try.

• Scatter a very light coating of straw mulch. I found this deters chipmunks from stealing my sunflower seeds, and it also seems to work on birds. The straw should be so thin you can still see soil through it. The seedlings don't have a problem poking through, and the chipmunks and birds must not like hopping about in the pokey-prickly straw. 
• Keep the soil slightly on the damper side if temperatures are warm. Whether from a dislike of muddy feet and beaks or some other sensory issue, birds don't seem to bother my seeds unless the top of the soil is dry. 
• Distract them with an easier food source. I'll scatter sunflower seeds (bird food) on the deck and other "safe" spots. Maybe a full tummy means a nap instead of pecking out my melon seeds? 

Be wary of critters once seedlings have sprouted as well. A local rabbit likes nothing better than to hop down my row of sunflowers when they're an inch tall and nip off each one just above the ground. They don't recover. If that happens, you'll need to reseed.