How Deep to Plant Seeds: A Simple Guide for Gardeners

One of the easiest ways to ruin seed germination is planting seeds at the wrong depth. Plant them too shallow and they dry out before sprouting. Plant them too deep and seedlings run out of energy before reaching the surface. Fortunately, the rule is simple once you understand it. We'll simply all of this in our planting guides which you can download in this article.

 🌱 Read More | When to Start Seeds Indoors in Canada: The Ultimate Timing Guide

The Simple Rule for Planting Depth

Most seeds should be planted two to three times as deep as their size. Small seeds need very little coverage, while large seeds need more soil on top. Here’s a quick way to think about it: 

Seeds That Should Be Planted on the Surface

Some seeds need light to germinate. These should be pressed gently into the soil without covering them. Common examples include:

• Lettuce

• Basil

• Celery

• Many flower seeds

Instead of burying them, lightly press them into the soil and mist with water.

Seeds That Need Shallow Planting

Many vegetables germinate best when planted just below the soil surface. Examples include:

• Tomatoes

• Peppers

• Broccoli

• Cabbage

These seeds are typically planted about 6 mm deep.

🌱 Read More | Seed Starting 101

Seeds That Need Deeper Planting

Larger seeds contain more stored energy and can push through deeper soil. Examples include:

• Beans

• Peas

• Corn

• Squash

These are usually planted 1–2 cm deep depending on the seed size.

Why Planting Depth Matters

Seeds rely on stored energy to push their first leaves toward sunlight. If planted too deeply:

• The seedling may run out of energy

• Germination slows dramatically

• The plant may never emerge

On the other hand, seeds planted too shallow can dry out quickly. The correct depth helps balance moisture, oxygen, and warmth.

Planting Seeds Indoors vs Outdoors

The basic depth rule stays the same whether seeds are started indoors or in the garden.

However, indoor seed trays dry out faster, so consistent moisture is important. Outdoor soil can crust after rain, so avoid burying seeds deeper than necessary.

A Helpful Planting Tip

When planting seeds indoors:

1. Fill containers with seed starting mix.

2. Water the soil lightly.

3. Plant seeds at the proper depth.

4. Mist the surface gently.

Keeping soil evenly moist encourages strong, even germination.

Common Seed Planting Mistakes

• Planting Too Deep: This is the most common cause of failed germination.

• Packing Soil Too Firmly: Seeds need oxygen as well as moisture.

• Letting Soil Dry Out: Seeds that dry out during germination often fail completely.

Quick Reference Chart 

Here are typical planting depths for common vegetables:

Always check seed packet instructions for specific varieties. 
Download our Seed Planting Depth Chart for easy reference.

Final Thoughts

Planting depth may seem like a small detail, but it has a big impact on germination success. Follow the simple rule of planting seeds two to three times their size, keep soil evenly moist, and most seeds will germinate reliably.

🌱  Download Caribou Seed Company Planting Guide ; an easy reference chart includes planting depth, soil temperatures, and germination times for many common vegetables, herbs, and flowers.