Planting seeds at the proper depth is essential for even germination and strong crops. When you start plants indoors, how much seed-starter mix you put on top of each seed can make or break your success:
Both situations can set back your spring gardening efforts. Striking a happy medium with seed depth will drastically improve your indoor seeding success. Here is everything you need to know about seed depth in indoor trays if you’re not sure how deep to plant your seeds.
You should plant garden seeds at a depth that is twice their largest dimension. That is, a pea or bean seed that is ½ inch long should be planted an inch deep. It’s best to plant lettuce seeds that are no more than 2 mm across and no deeper than ¼ inch deep. Just sprinkle a little soil on top of them. What if you plant a seed too deep or too shallow? It might not get the right conditions to grow.
Improper seeding depth is one of the most common seed-starting mistakes that beginner gardeners make. You should never sow a seed deeper than twice its diameter. In other words, seeds need to be planted about twice as deep as they are wide.
However, there is no need to take out a microscope and measuring tape. Simply remember these general rules:
Larger seeds like squash and beans tend to require deeper containers and more soil to ensure germination. Otherwise, they will dry out, get eaten, or germinate with exposed roots. Plant 2-3 times deeper than the width of the seed. It’s okay to plant these seeds too deeply, but they won’t do well if you plant them too shallow.
Medium-sized seeds like brassicas and tomatoes should be placed in a hole that is twice their size. Gently backfill to ensure that the seed can easily reach the surface.
You can lightly sprinkle seed starter mix or “topper” mix on top of the soil and press very small seeds like basil and lettuce into it. These crops are the most sensitive to light and moisture. Sowing too deep will kill the seed.
How Deep Should You Plant Flower Seeds? A Beginner’s Guide
Deciding how deep to plant flower seeds can seem tricky for beginners. But following some simple guidelines will help your seeds thrive. In this comprehensive guide, we’ll cover everything you need to know about proper planting depth for flower seeds.
The General Rule of Thumb
The general rule of thumb is to plant seeds at a depth equal to two or three times their width. So if a seed is 1⁄4 inch wide, plant it 1⁄2 to 3⁄4 inches deep. This rule applies to most flower varieties.
Planting too shallow is better than planting too deep. Seeds planted too close to the surface risk drying out. But seeds buried too far down may not break through the soil or may use up their stored food source before emerging.
When in doubt, err on the side of planting a little too shallow You can always add more soil on top, but you can’t dig up seeds once planted without disturbing their delicate roots
Factors that Determine Planting Depth
Several factors determine the ideal planting depth:
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Seed size – Large seeds are planted deeper than tiny seeds, Larger seeds contain more stored nutrients to help them emerge from deeper in the soil,
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Soil type – In light, sandy soil, plant slightly deeper than in heavy, clay soil, which is denser for tender shoots to penetrate.
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Climate – In hot climates, plant deeper to protect seeds from drying out on the surface before sprouting. In cool climates, planting too deep will hinder germination.
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Light requirement – Seeds needing light to germinate, like alyssum and begonias, are merely pressed into the soil surface rather than buried.
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Seed variety – Check the seed packet for any special planting instructions. Certain flowers have specific depth requirements.
This table provides a general planting depth guide based on seed size:
Seed Size Planting Depth
Fine, dust-like 1/8 inch
Medium, like tomato seeds 1⁄4 inch
Large, like beans 1⁄2 to 1 inch
Extra large, like peas 1-2 inches
Preparing the Soil
Before planting, prepare the seed bed to optimize conditions for germination. Loosen and smooth the soil, removing any rocks or debris. Rake to a depth of at least 6 inches. This allows tender roots to penetrate down and anchor the sprouting plants.
Moisten the soil before planting. Seeds need consistent moisture to swell and crack open. Water thoroughly the day before planting. Test the soil – it should feel damp but not soggy. Add water if the top few inches are dry. Proper soil moisture encourages seeds to emerge evenly.
Planting Techniques
Now that your soil is prepped, it’s time to plant! Here are some tips for placing seeds at the correct depth:
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Poke holes to the recommended depth with a pencil, chopstick or specialty seeding tool. Carefully drop in 1-2 seeds and re-cover with soil. Space holes according to seed packet directions.
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Make a furrow with a trowel by slicing into the soil. Sprinkle in seeds and cover back over with surrounding soil or fine vermiculite.
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Very small seeds can be sprinkled directly on the prepared soil bed and gently pressed in with your hand or a flat board.
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Larger seeds can be buried individually in a small mound of soil. Scoop soil into a mound, poke a hole to the proper depth, insert the seed and cover with surrounding soil.
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Pelleted seeds have an outer coating that aids in planting depth. Simply place them where desired on the soil surface; no need to cover. The pellet protects the seed yet allows water and air to permeate.
Provide Ideal Growing Conditions
Once planted, be diligent about providing optimal growing conditions so your flowers sprout successfully:
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Keep seeds moist continuously. Gently mist the soil surface whenever it dries out. Don’t let it become crusted.
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Allow plenty of light. Most flowers need at least 6 hours of direct sunlight daily for robust growth. Rotate containers or thin surrounding plants as needed.
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Maintain proper air circulation around plants, and avoid overcrowding.
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Remove any sprouted weeds to prevent competition for water and nutrients.
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Once sprouted, check if seedlings need to be thinned according to spacing guidelines.
Troubleshooting Issues
Seed starting presents some potential pitfalls. Here are some common issues and how to resolve them:
Problem: Seeds failed to germinate or had spotty germination.
What About Direct Sowing?
Grass or wildflower seeds will germinate if spread over the soil.
Some seeds can grow right on top of the soil, but most garden seeds need a layer of soil on top of them to keep them from drying out or being eaten by bugs.
Of course, there are robust seeds that will sprout just about anywhere. Seeds that tolerate shallow sowing are often those that are closely related to their wild plant ancestors.
Most grass seed or wildflower seed that you sprinkle on a bare patch of ground will grow if it rains enough. However, vegetable and fruit seeds tend to be much more finicky. The best way to grow them is to plant the seeds at the right depth in seed-starter mix or rich garden soil.
Risks of Sowing Too Shallow
Seeds that are not planted deep enough may dry out before they can sprout.
Planting a seed too shallow can cause low germination or seedling death. Seeds that aren’t tucked deep enough into the soil often dry out before they can sprout. They are also vulnerable to injury or displacement from pests, diseases, flooding, and wind.
If you sow a seed too shallow, it is more susceptible to:
When wind or air moves over the seed-starting tray, the soil mix on top dries out more quickly. Seeds are very sensitive to moisture during their early stages. If a seed is exposed to dry air during the germination process, it could stop germination, slow growth, or even kill the plant.
When a seed doesn’t have proper seed-to-soil contact, it is more prone to floating away with irrigation water. When you water your seed trays, the seed could become dislodged and drift out of the container. What’s worse is that water can easily damage a new root system that isn’t fully rooted in the soil.
Some places where you plant seeds may have air currents and fans that could blow away very light seeds that are planted just below the surface. Even though this is more common in garden winds outside, you should still be aware of it in your home or greenhouse.
A seed that isn’t properly “tucked in” becomes an easy target for hungry insects. Rodents can also do a lot of damage to seeds that are too close to the ground in a nursery or greenhouse. For example, cucumber seeds are absolute magnets for hungry mice and voles. Sometimes, they’ll even dig the seed out of the soil!.
Shallow seeding is most problematic for large-seeded crops. Imagine a pumpkin seed trying to germinate on the soil surface. It might dry out or its fragile developing roots would be exposed to the scorching sun. These larger seeds need the moist darkness deep in the soil to properly sprout.
On the other end of the spectrum, some very small seeds need light that has been filtered in order to wake up and start growing.
They can actually do better with shallow planting as long as you press them into the ground and sprinkle some seed starter on top of them. For example, lettuce, poppies, snapdragons, and many wildflower species benefit from shallow seeding.
Understanding Seed Planting Depth and Why It Matters
FAQ
Can you just throw flower seed on the ground?
Is it better to plant seeds deep or shallow?
How do you properly plant flower seeds?
Can you plant seeds too deep?