If you want to start your own plants from seed, the first step is to get them to germinate. This depends on soil temperature, moisture, air, light, and planting depth.
So, can you plant seeds too deep? It is possible to plant seeds too deep, in which case they will either fail to germinate, stay below the soil after sprouting, emerge late, or grow poorly after emerging from the soil. A good rule is to plant seeds at a depth of 2 times their diameter.
Of course, there are some seeds that only need a shallow layer of soil covering them. A few seeds don’t need to be buried at all or need light to germinate.
In this article, we’ll talk about how deep to plant seeds and what happens if you plant too deep. We’ll also talk about what to do if you plant your seeds too deep or if they fail to germinate.
Let’s get going.
Can You Plant Seeds Too Deep?
You can plant seeds too deep, but the proper depth depends on the type of seed (more on this later). Planting seeds too deep can cause a variety of problems, which we’ll get into now.
What Happens If You Plant Seeds Too Deep?
When you plant a seed too deep, it may not get the warmth, moisture, light, and air that it needs to germinate. This can lead to several problems, including:
- Failure to germinate – When seeds are planted too deep, there is a chance they won’t get enough water to germinate. After all, seeds will only sprout if they are kept moist.
- Low germination rate – even if some seeds germinate, you may see a lower germination rate, which will result in wasted seeds and empty space in your garden.
- Slow germination – seeds that are buried too deep make take a long time to sprout, possibly due to lack of water.
- Delayed Emergence – seeds that germinate will still need to “push” their way through the soil to reach the surface for air and sunlight. According to the Michigan State University, seeds that are buried too deep will take a longer time to emerge and start producing energy from sunlight (if they ever emerge at all!)
- Lost time – when germination and emergence from the soil is delayed, your plants lose precious time that they could have spent growing. This is a much bigger problem in cold areas with a short growing season. In some cases, there might not be enough time to replant if your seeds do not germinate on the first attempt.
When choosing a container for starting seeds, choose one that has enough space to bury seeds deep enough. Make sure there is also enough space for plant root development until you can repot or transplant into the garden.
If you are starting lots of seeds all at once, try a standard size 1020 seed germination tray.
How Deep Should Seeds Be Planted?
According to the University of Maryland Extension, a good rule for most plants is that a seed should be planted at a depth of about 2 times its diameter. For example, if a seed is ½ inch in diameter, then it should be planted at a depth of 1 inch.
This suggests that larger seeds will be buried deeper, which makes sense. A larger seed has more stored energy and nutrients, so it can grow more before it needs sunlight to start producing energy.
Of course, the proper depth for a seed will depend on the type you are planting. According to the University of Georgia Extension, you should press small seeds (such as onions) into the top of the soil with only a thin layer of soil covering them.
Other seeds should not be buried under any soil at all. For example, the following plants need light to germinate:
The type of soil also makes a difference in how deep you plant your seeds. Plant seeds deeper in light sandy soil and shallower in heavy clay soil.
Here is a list of some common garden favorites and their recommended planting depth:
|Beets||1/2 in||65-85 F||4-6|
|Carrots||1/4 in||65-85 F||6-7|
|Corn||1 in||65-95 F||3-7|
|Cucumber||1/2 in||65-95 F||3-6|
|Lettuce||1/8 in||60-75 F||2-4|
|Pepper||1/4 in||65-75 F||8-12|
|Pumpkin||1 in||85-95 F||3-10|
|Spinach||1/2 in||65-75 F||5-6|
|Squash||1 in||85-95 F||7-14|
|Tomato||1/4 in||65-85 F||6-8|
Note: this list is not exhaustive by any means. You can find a more extensive list of vegetable planting depths from the University of Georgia Extension.
If you have any doubt about how deep to plant your seeds, consult the seed package itself, or check the seed catalog or website where you bought them.
What To Do If You Planted Seeds Too Deep
If you planted your seeds too deep, don’t despair. You might still be able to salvage some or all of them.
First, check to see how long the seeds would normally take to germinate. This page from the University of California has some good information on the time to seed germination, based on soil temperature.
If your seeds have already been planted for longer than the germination time, they might be buried too deep. In that case, remove some of the soil that you put over them. (This is when it comes in handy to mark off where you planted your seeds!)
If your seeds have not had enough time to germinate, you have two options. One is to leave them for a while and see if they germinate.
The other option is to remove some of the soil so the seeds are not planted so deep.
You can always hedge your bets by planting some more seeds at the proper depth. The worst case scenario is that you get extra produce, which you might have to give away to friends and family (they probably won’t mind!)
What To Do If Seeds Don’t Germinate
If your seeds don’t germinate at the proper planting depth, there are a few possible reasons for it.
Seeds Not Germinating Due To Temperature
Soil temperature is one of the most important factors that affect seed germination. When soil temperature is in the proper range, seeds germinate faster, and you get higher germination rates.
For example, tomato seeds can germinate in 6 days when the soil temperature is 86 degrees Fahrenheit (30 degrees Celsius), but they can take 43 days when the soil temperature is 50 degrees Fahrenheit (10 degrees Celsius).
High soil temperatures in the 90’s or above will stop many seeds from germinating at all. However, cold soil temperatures are much more common.
Many seeds will take a month or more to germinate in soil colder than 50 degrees Fahrenheit – if they ever germinate at all. So, make sure that you are keeping the soil warm enough to allow your seeds to germinate.
If you start seeds indoors, you can do this with a heat mat. Some grow lights will also give off some heat to keep your plants warmer.
If you planted seeds outdoors, you can keep the soil around them warmer by using a garden cloche. You can learn more about garden cloches in my article here.
Seeds Not Germinating Due To Moisture
Seeds also need moisture to germinate. An extreme in either direction will prevent seeds from germinating.
If the soil is too dry, it does not send the signal to seeds that it is time to start sprouting. If the soil is too wet, then seeds will not get enough oxygen, which they also need to sprout.
When starting seeds indoors, a spray bottle is helpful for keeping the soil moist without over watering. If planting seeds directly in the soil outdoors, a drip irrigation system can help to keep the soil moist but not soaking wet.
Seeds Not Germinating Due To Air
Seeds need oxygen from the air to germinate. A lack of air is common in soil that is hard and compacted.
A lack of air is also common in over watered soil, since the water takes the place of air between the soil particles. Avoid packing down the soil over your planted seeds, and don’t leave the soil too wet after watering.
Seeds Not Germinating Due To Light
Some seeds need light to germinate, such as celery, dill, lettuce, and petunias. If you bury these seeds too deep (or at all), they may not germinate.
What Happens If You Plant Seeds Too Shallow?
At the other extreme, planting seeds too shallow can also cause problems. For one thing, the seeds may dry out and fail to germinate if water evaporates out of the soil too fast.
Even if seeds do germinate in shallow soil, they may work themselves out of the soil as they grow. For example, if you plant peas too shallow, they may come up above soil after sprouting.
If you planted your seeds too shallow, put a little more soil over them and give them another chance. You can also plant some extra seeds to hedge your bets and thin out the weaker plants later in the season.
Now you know what happens if you plant seeds too deep. You also know what to do to salvage seeds that were planted too deep.
You might also want to read my article on pelleted seeds and when you might want to use them.
I hope you found this article helpful. If so, please share it with someone who can use the information.