Our visiting professor digs into tomato planting depth

With Ray’s recent photos of the peach, crabapple, and hydrangea planted too deeply, a discussion of tomato planting depth arose in the comments. I’ve seen the prolific adventitious roots start to form near the base of tomato plants, and I plant tomatoes to the cotyledon or deeper, but tomato planting depth not an area I have extensive research experience in. So I did a little literature search.

It seems that the practice of planting tomatoes is more than just friendly garden folklore. There’s some evidence that it works. Or, at least it works sometimes. Early in the season. And maybe not everywhere. Oh these darn scientists, with their wishy-washy caveats.

There just isn’t a whole lot of peer-reviewed research on the subject. One of the recent papers (from 1996) cites a “Crockett’s Victory Garden” (circa 1977) as a source of information for Northern gardeners about the benefit of deeply-planted tomatoes. Jim Crockett was no horticultural slouch, but just because successful gardeners do something doesn’t mean it’s sound practice (but like I said, I do it too…).

Southern tomato growers, on the other hand, have some peer-reviewed evidence to go on. It seems that in some years and some locations in Florida, tomatoes planted to the first true leaf were able to be harvested earlier (Vavrina 1996) than if they were planted to the top of the root ball. The overall trend was for a bit more and a bit larger fruit per plant. The paper is pretty sparse on detail (statistics and design), but that’s what they conclude. Similarly, a study of fall-planted tomatoes in Louisiana (Hanna, 1997) showed a benefit of planting to the first true leaf instead of to the top of the root ball in two years at one location. In that study, treatments that lowered the root zone temperature tended to increase yield. If you can get an extra 3 pounds of medium or larger tomatoes from a 50 square foot plot in some years, what’s the harm? Deep planting certainly helps prevent lodging in tender young plants, so there’s a clear benefit there if the supports aren’t adequate.

Most of the work suggests that, like mulch, deep planting helps to moderate root temperature, and fluctuating or high root temperatures are stressful to the plant. I can get behind that I suppose, but it’s hot in Florida and Louisiana in the summer. What about stuff planted in Minnesota, where I live? We use plastic up here to get warmer soil temperatures at planting, not cooler temperatures!  Well, I didn’t find any work on that.  But interestingly, some of the yield benefit seen in planting peppers to the cotyledon or true leaf in Florida (equivalent to 5 extra pounds per 50 square feet, in 3 of 4 years, with commercial spacing and fertilizer rates; Vavrina, 1994) don’t show up in Massachusetts (Mangan, 2000). But deep planting did help prevent lodging, which allowed for faster crop maturity in both places.

So the verdict on deep planting tomatoes? It doesn’t hurt, it helps sometimes, and it helps prevent lodging, so why not? One caveat: don’t plant grafted tomatoes deep. The scion will make roots, negating some of the benefit of the rootstock.

(And an addition from Linda:  here’s a diagram from TAMU demonstrating planting depth for tomatoes; this link will take you to the article itself.)

11 thoughts on “Our visiting professor digs into tomato planting depth”

  1. I guess it can’t hurt to plant them deep then, and it may even help. In a way I did what Ray did, but in the opposite direction. I was applying my knowledge of proper tree planting to tomato planting. But like I said, I still had good success with my tomatoes, even if not all of them ripened in time but that’s probably because I started a bit late and our growing season isn’t very long.

  2. Thank you for the detailed review!

    Still I just cannot bring myself to bury plants that deep.
    I noticed that the lower leaves get soil backsplashed during heavy rains and the leaves get early blight damage pretty soon.

    Maybe in a commercial setting with black plastic mulch and preventative antifungal spraying deep planting makes sense but not in my mandatory-organic community garden. I resort to planting halfway through cotyledons and aggressive pruning of lower leaves to control fungal diseases.

  3. Lu, that sounds like a great compromise. Another compromise for gardeners is to use thick straw mulch. That will a) keep weeds down, b) help prevent big swings in soil moisture (and thus helping to prevent blossom end rot), c) help hold young plants upright (similar to deep planting), and d) prevent soil from splashing on lower leaves and fruit.

  4. Not a scientist, but I always plant my tomatoes deep to the first true leaves. Fungal problems are a matter of course for us Southern gardeners. I apply a dense bed of pine straw mulch under my plants and use resistant varieties. I have seen no greater evidence of fungal disease on deep planted tomatoes than when I just planted them to the root ball.

  5. I’ve tried it both ways up here in Western New York and planting deep is superior. Not only will it increase the root mass but it gives better structural support to the plant which is especially important in high winds and when the plant is top heavy with fruit.
    Another benefit I think is plausible is since the roots are closer to the subsoil they can more easily access those nutrients and minerals that have leached down into the subsoil.
    The subsoil here is high in clay, therefore has a high CEC.

  6. When I took my first stab at growing tomatoes seventeen years ago, an elderly Italian neighbor instructed me that I must plant them deep – it’s never failed me here in Southern New England.

  7. Great article! Taking the research one step further, I’m thinking it means that those “Topsy Turvey” (upside-down) tomato planters are a bad idea here in the south because the roots would get super hot while baking in the sun all day like that.

  8. Martha, that’s a good point about tomatoes in pots. But some people don’t have any place to put tomatoes in the ground, so a pound from a pot is better than not having any plants at all!

  9. I’ve got Jim Crockett’s book beside me as I read this article. 😉

    I just watched a YouTube video from a guy who planted tomatoes deep and then later dug up the plants and cleaned off the roots. What he found was a root ball at the bottom of the plant, and then a web of roots growing just under the soil surface, with no roots coming off the buried stem in between. There was more root mass at the upper level than in the original root ball. Which suggests to me that it probably doesn’t help a lot to bury the roots too far down vertically. Of course, I also learned to lay plants down in a trench and turn up the growing stem. This would keep the root-producing buried stem near the surface, where the plant gets most of its water.

  10. MarkB: As I mentioned above, some of the benefit of deep planting is to reduce lodging, so there is at least some benefit no matter where the roots grow. But I’m not surprised by what you saw in the video, roots will grow where the resources are easiest to get. One of my favorite photos of plant development shows the effects of nitrogen placement at different soil depths on root growth. I don’t know if the HTML code will work in this comment, but if not, copy-paste the link. [URL=http://imgur.com/qfGUy][IMG]http://i.imgur.com/qfGUy.jpg[/IMG][/URL]

  11. Trench planting, laying the rootball & plant in a shallow trench near the surface of the soil, likely has more benefits in northern areas where heat is an issue compared to setting the rootball deep.

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