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Is it worth planting your tomato deeper in cold climates? In particular in Canada where the soil can be cooler till later in the year. The answer may be surprising … it was for me. This has been my garden heartbreak of the year because my tomato planting regime was the deeper the better.
If you are new to this blog my name is Ashley and I am a soil scientist. I am located in a Canadian Zone 3 and a USDA Zone 4. I write articles, and make YouTube videos, Instagram & Facebook posts all designed for Canadians and Cold Climate gardeners using science-based methods. If you are looking for anything specific be sure to let me know in the comments down below.
What Does Science Say About Planting Tomatoes Deeper?
To be completely honest the information on this is surprisingly murky. There are not a lot of peer-reviewed studies and even fewer when it comes to a definitive conclusion. This next part I am about to outline is going to rock the boat but this is my literary research the following is a general consensus.
- Planting tomatoes deeper protects the roots from temperature stress in two ways.
- Wild fluctuations in hot/cold soil can stress out our plants. The deeper our primary root system is the less likely it is to be exposed to rapid temperature changes
- Cooler roots – Overall as we get lower in the soil profiles we see colder temperatures. These cooler temperatures in a hot environment can help the plant regulate itself in times of extreme heat.
- Planting tomatoes deeper gives the plants more support and structure.
The depths in which the plants were included root balls, cotyledons & first true leaves… not as far as you can make it fit. The plants that were planted to a depth of the first true leaves yielded the highest number of large fruits. Whereas the root ball placed plants yielded the lowest. BUT… These studies were performed in Florida and not in a cold climate like Canada.
Is Planting Your Tomatoes Deeper In Canada Worth It?
Assuming you are following the direction of not planting past the first true leaf you may see benefits in regards to lodging prevention. But when it comes to yields we may actually see a decrease due to how cold our soil can be. You can say thank you to the Canadian frost line on this one.
Let’s dive deeper… with our tomato roots
Okay, so this is where I go a bit rouge and start making my own educated guestimates. But stick with me here in the name of science! Below is a chart with rough estimates of soil temperatures by depth during the peak summer months. These temperatures will vary based on factors like air temperatures, soil moisture, bulk density & solarization. I collected data to a depth of 5ft, as a typical tomato root system only goes to a depth of 2 feet when directly sown.
This means if we were to dig our tomato plant up to a depth of one foot to hit the first true leaves we likely will have roots somewhere between the 2-5 foot range.
| Soil Depth | Florida | Canada On Average |
| 10 cm | 27 | 20-27 |
| 2 ft | 24 | 19-23 |
| 5 ft | 20 | 17-19 |
From the chart above we can see it’s going to be determined by where you are in Canada. My recommendation is to become your own garden scientist and use a soil thermometer combined with experimenting. You want to make sure the zone you plant your tomato roots in is more than 9 celsius when transplanting outside. Ideal root-soil temperatures for tomatoes will be about the 20 degrees Celsius mark.
This means in colder locations such as zone 3 & 4 you may not see any gains from planting the tomato deeper. The solution to this would be to use plastic to solarize the soil and warm it up prior to planting. The longer the roots stay below 20 the more it can harm the end harvest. This year I intend to do some testing in my own garden to see how it alerts the end yields.
If you choose to plant tomato plants deeper follow these rules
There are some rules you will want to follow when planting tomatoes below the root ball in Canada.
- Do not plant past the first true leaves.
- Plant either the root ball, to the cotyledons or the first true leaves.
- Test your soil temps. Where your root ball is touching it should be ideally 20 degrees celsius but can be as low as 10 for a temporary period of time.
- To help heat the soil to further depths try using clear plastic sheets. But make sure you are not overheating the root.
- Channel your inner garden scientist and try different ways of planting tomatoes to see what works best for you.
Planting Tomatoes Deeper During Bumping Up
If you bump up your seedlings you likely plant them deeper. After all the benefits you have been told it makes sense! But technically if while bumping up you sink the seedling in past the first true leaves you are done for the year! This is if you are trying to copy the Florida study to a tee.
Be sure to mark down the depth your bump-ups were placed in order to prevent planting them too deep in the spring. If they have been pre-planted lower then simply transplant outdoors to a depth of just the root ball.
Planting Tomatoes On Their Side
This is a great solution for helping plants achieve support without the stress of planting lower in cold soils. My one word of caution is to limit hard right angles that may cause breaking or stem stress. This has always been my major concern because most photos on this show a drastic angle.
If you are gardening in Canada this method of planting will allow you to achieve the benefits of temperature regulation and support without the temperature stress of planting deeper in the soils. You still want to follow the same rules of ensuring the plant is only buried to the first true leaves at most.
So Is It Worth Planting Your Tomato Deeper In Cold Climates? It is going to come down to the depth and soil temperatures. If your soil temperatures are below the desired 20 degrees Celcius in the lower levels consider the side planting method. This is going to allow for the benefits of support & temp regulation without the stress.
Ultimately this one is going to come down to personal preference for Canadians. The lower depth planting definitely helps with stem support and prevents lodging. And for those of you that live in areas where the soil tends to get warm, planting the root ball at a depth that hits 20-degree celsius will maximize yields. But for those Canadian gardeners that have cool soils, the deeper planting depth can cause more harm than good.
