How Deep To Plant Seeds

As home gardeners, it’s common for us to grow a variety of vegetables, herbs, and flowers from seed. Seeds are generally inexpensive to purchase, and there’s an enormous pleasure to be had from watching a plant grow to full size from a tiny seed.

Generally, seeds should be planted no deeper than around 2 or 3 times the width or diameter of the seed. It’s far better to plant the seed shallower than to plant it too deeply. 

To understand why, here’s a more detailed explanation.

How Deep Should You Plant Most Seeds?

Seeds need to be planted just deep enough to allow good germination so that the shoot can break through the surface of the soil. Each seed is stored energy for the emerging plant. This amazing little embryo stores just enough energy to produce the first root or two and the first shoot or seed leaves.

These seed leaves are called cotyledons and are usually far different from the mature leaves of the plant. They are designed to use the sun to help the tiny plant to start its growth. Therefore, if seeds are planted too deeply, the seed will run out of stored energy before the seed leaves have broken through the surface of the soil.

So, if we follow the general rule, large seeds like beans and peas can be sown deeper than smaller seeds like those for spinach and Swiss chard. On the other hand, really tiny seeds can just be broadcast over the soil and then lightly pressed in without covering them with any more soil.

When sowing seeds of any variety, it’s always a good idea to check the seed packet for specific instructions. This is because some seeds actually require light to encourage germination. Therefore, these specific seeds should just be spread over the soil and only very gently watered.

Even though sowing seeds too shallow is better than sowing them too deeply, this can pose a few problems as well. This is because some seeds need darkness to germinate effectively. Another problem is that the soil that is close to the surface dries out much faster, and the lack of moisture can affect germination.

As you can see, there’s a lot of science behind achieving perfect germination of seeds, and their sowing depth is quite important. Bear in mind, though, that nature has designed seeds as a survival method for plants, so plants that self-seed in the wild will always have some seeds that will germinate no matter where they end up in the soil.

Seed Depth Planting Chart

To help make this a little easier for you, here’s a chart that gives you the approximate planting depth for a variety of different seeds.

Plant VarietySeed Planting Depth
Arugula¼ inch (6mm)
Bush beans1 to 2 inches (25 to 50mm)
Pole beans1 to 2 inches (25 to 50mm)
Beets½ to 1 inch (12 to 25mm)
Broccoli¼ inch (6mm)
Brussels Sprouts¼ inch (6mm)
Cabbage¼ inch (6mm)
Carrots¼ to ½ inch (6 to 12mm)
Cauliflower¼ inch (6mm)
Celeriac1/8 inch (4mm)
Celery1/8 to ¼ inch (3 to 6mm)
Collards¼ inch (6mm)
Corn1 to 2 inches (25 to 50mm)
Cucumbers½ inch (12mm)
Eggplant¼ to ½ inch (6 to 12mm)
Endive¼ inch (6mm)
Kale½ inch (12mm)
Leek¼ inch (6mm)
Lettuce¼ to ½ inch (6 to 12mm)
Melons½ inch (12mm)
Onions¼ to ½ inch (6 to 12mm)
Peas1 to 2 inches (25 to 50mm)
Peppers¼ inch (6mm)
Pumpkin1 inch (25mm)
Radicchio1/8 inch (3mm)
Radish¼ inch (6mm)
Spinach½ inch (12mm)
Squash1 inch (25mm)
Strawberries1/8 inch (3mm)
Swiss Chard½ inch (12mm)
Tomatoes¼ inch (6mm)
Watermelon½ inch (12mm)
Zucchini½ to ¾ inch (12 to 19mm)

How To Plant Seeds

The best way to plant seeds into the garden is to prepare the soil so that it’s open and friable. Once you’ve done that, the easiest way to plant a row of seeds is just to make a small drill that is just deep enough for the variety of seeds that you’re sowing. You can use a small trowel or another suitable garden tool for this.

Then, scatter the seeds inside this drill. For smaller seeds, spacing is not so important as some of the seeds will germinate and some won’t. Once germination has occurred, the seedlings can be thinned out to give adequate space between the plants.

For larger seeds such as peas and beans, you should space them according to the instructions on the seed packet. However, it’s always a good idea to place 2 or 3 seeds together as it might be a case that not all of them will germinate.

Once you’ve scattered the seeds, just gently backfill the drill to cover the seeds and only gently firm down the soil. You don’t want to compact the soil at this stage because the young seedlings will have trouble breaking through.

For tiny seeds, creating a drill is not necessary. Just scatter the seeds on the surface of the soil and then sprinkle a small amount of soil, sand, vermiculite, or seed-raising mix over the top.

There are some seeds that need light to germinate. These include dill and lettuce and some flower varieties such as petunias, sweet alyssum, and coleus. All you want to do with these seeds is scatter them over the surface of the soil and gently press them down with your hand to ensure good soil contact. Do not cover these seeds with any additional soil.

Watering Your Seeds

Newly planted seeds need adequate moisture to germinate well. Therefore, you need to water gently once you’ve planted your seeds. Use a hose or watering can with a rose attachment. Be sure to water very gently so that you don’t dislodge the seeds when you do this.

Depending on your climate and the time of year that you’re planting, it’s a good idea to gently water your seeds on a daily basis. The idea is not to let the top layer of the soil dry out. It should be kept moist at all times but not too wet, either.

Once the seeds have germinated, it’s time to thin them out. This gives the growing seedlings enough room to grow. Check the seed packet to determine the correct spacing of each variety of plants. Then, just remove the weakest seedlings to give the strong ones plenty of room to grow.

Be very careful when you do this so that you don’t dislodge the little plants that you want to retain. Using a small pair of scissors or snips can sometimes be useful to just cut the base of the seedlings you want to cull instead of actually pulling them out. This ensures that the soil around the plants stays intact and that the roots of the surviving plants are not disturbed.

Keep a close eye on your young seedlings and ensure that they’re receiving adequate moisture, and don’t let them dry out. If you do all of this correctly, you’ll soon be able to harvest some lovely fresh vegetables and herbs from your garden.

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