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Learn how to use the adventitious roots on your tomatoes, tomatillos, and other garden plants for healthier seedlings and more productive adult plants.
When you think about plant roots, you probably think about the branched network of underground plant material that a plant uses to slurp up water and nutrients. Those are referred to as a “primary root system.”
However, some plants are also capable of producing other types of roots that don’t necessarily form underground – one of the most useful of these for the home gardener is “adventitious roots.”
Have you ever had a garden plant like a tomatillo or tomato flop on to the ground, been too lazy or forgetful to upright it, then come back weeks later to find its above-ground stems rooted into the ground?
Have you ever noticed your sweet potatoes or winter squash plants climbing along the ground and setting roots at each leaf joint? Those are adventitious roots!
What Are Adventitious Roots?
Although the word “adventitious” implies “chance,” adventitious roots are anything but accidental.
Some plants have developed the ability to program their cells to adapt to whatever conditions they find themselves in. Up in the air? The cells will program to grow as stems or leaves. Moist conditions or contact with soil? The cells will program to become roots.
Before you think you can go out and bury your plants and they’ll just develop new root systems, please note that not all plants have adventitious roots. For instance, if you bury the base of a cherry tree, you’re probably going to cause the plant to die rather than develop new roots.
However, for certain types of plants, you can use their ability to form adventitious roots to your advantage, growing healthier seedlings and more robust, productive, and resilient plants…
Using Plants’ Adventitious Roots In Your Garden
Two of our favorite plants that form adventitious roots are tomatillos and tomatoes. Notice those nice fuzzy stems in the above picture? Each one of those little “fuzzies” has the potential to be a root.
This feature comes in handy at two stages when you’re growing tomatoes and tomatillos:
1. Potting up seedlings.
We often start our seeds in Ladbrooke soil blocks or small cells to conserve space. This means we have to “pot up” the seedlings into larger containers about 4 weeks after they’ve germinated so they don’t get too root bound.
When we pot up our tomatillos and tomatoes, we:
- Remove the two cotyledon leaves (the first leaves that emerge after the seed germinates), and
- Bury the entire plant, stem and all, a couple of inches below the next set of branches.
This allows the seedlings to form a more extensive root system, which translates into greater water and nutrient uptake potential.
2. Transplanting outdoors.
As we wrote about in 5 Tomato Growing Tricks (our most popular article ever), we also take advantage of adventitious roots when transplanting our tomatillos and tomatoes outdoors.
Rather than simply plunking the root ball in the ground, we again remove the lowest branches/leaves, then bury the plant on its side. If you live in warmer climates, you can simply dig a deeper hole and put the plants in the ground vertically. However, doing this in cooler climates means your tomato plants’s roots are in cooler soil, which can reduce fruit set, hence our recommendation to bury the plants sideways.
If you’ve never used this method before, it can make you feel like you’re doing something wrong and/or killing your plants. However, what you’re doing is creating a more extensive root system and setting yourself up for healthier plants that need less irrigation and fertilization because they have a more extensive root system.
Three warnings about adventitious roots:
1. Plant disease introduction
As Clemson University Extension mentions, a possible risk with removing the lower leaves/stems and burying your tomato transplants is the potential for disease organisms to infect your plants through the wounded tissue (example: bacterial wilt).
If you’re rotating crops and/or using good compost or worm castings in your planting holes (here are the worm castings we recommend), you can minimize the likelihood of plant infection.
2. Colder climates, lower yields
We live in a warm, southern climate, and the tips outlined above work great for us. However, we’ve heard from a good grower living in a cooler climate who says that their tomato plants don’t produce as much when they bury the roots during transplant.
They speculate this is because tomato plants love heat, and burying them too deep keeps their roots in cooler soil, which may inhibit productivity. If you live in a cooler climate zone, experiment with different methods to see which works best for you. As mentioned above, this is why we recommend transplanting your seedlings sidewise into a trench rather than into a deep vertical hole.
3. Not all plants can grow adventitious roots
We can’t repeat this warning enough: not all plants can grow adventitious roots! If you bury a plant that can’t grow adventitious roots, you’ll kill the plant.
If you’re working with a new plant variety, do a bit of research to make sure you’re only using this method on plants that can grow adventitious roots.
We hope this information about adventitious roots helps you enjoy even more juicy, sun-ripened tomatoes and tomatillos this year.