You might have seen some videos of gardeners growing plants from stems in a glass of water that quickly gets filled with shiny white roots. Those are water roots and are way different from those roots that your plant will grow into the soil. This also affects its growth quite significantly. Here’s why.
The differences between water roots and soil roots are a consequence of adaptation to their environment. Water roots present more hair, are whiter, more fragile, require less energy to develop and they can breathe in water compared to soil roots.
What is essential to know about water and soil roots is how each is beneficial in the different stages of growing your herb indoors. A plant cutting in a glass of water is always a good start, but most of the time, those water roots need to be converted into soil roots to allow your herb to grow further.
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The first difference between soil roots and water roots is in their physical structure. Soil roots are thicker, having to reach further and deeper than water roots to access enough nutrients and water for. Due to the easier access to water and nutrients, water roots are thin, small, and relatively fragile.
Another difference between water and soil roots is in their energy requirement. Water roots require less energy and time to grow compared to soil roots. Indeed, it is a common practice to start plants (often stems) in a cup of water, and only after they develop the first roots (water type) transfer them to the soil.
The third difference between water and soil roots is in the root hair. Water roots, being constantly submerged, are finer, and have more hairs.
Water roots evolved to breathe underwater. They can extract oxygen that naturally dissolves in water through also a higher surface porosity (more gas can go in and out), as discussed in this study. Soil roots are not able to do that. That also explains why they tend to suffocate (and then rot) in case they are waterlogged.
Finally, the fifth difference is in their color. Water roots are generally white, whilst soil roots tend to be yellowish or brown (partially due to the soil). Be careful; discoloration, such as brown water roots, mushy, and light brown, are an indication of root rot.
Getting a plant started inside can be a difficult process. Provided the many herbs (someone says basil!) easily develop water roots, it is often the easiest path to start a plant. Also, do not forget the rewards in seeing the roots develop through a shiny glass!
Though thin roots will develop at first, it is possible to grow thick soil roots from water roots— over time (see propagation below). Soil roots are the goal if you want to have long-lasting indoor herbs. This is because water roots cannot support very much growth if not through a hydroponic (on this more at the end of the post).
Simply leave the stem in water until the water root reaches an inch or so. In my experience with basil and mint, water roots will start developing in 2-3 weeks, so I need to be patient. Remember to change the water (every other day is enough), and then begin the process of propagation to transfer the plant into the soil. The plant will naturally transition from water roots to soil roots if propagation is done correctly.
Unsure how long it takes and how to do it? Check the article below.
Here’s the kicker
You can overwater your stem when propagated in water. The plant survives off the balance of sunlight and water— so if the plant is not getting enough sunlight, it may drown. The easiest solution to this is to keep your water-borne plants in a sunny spot!
Roots tend to rot in a high moist environment that allows specific types of bad bacteria (presents in all soils) to develop. However, water roots started in tap water and kept in a glass will rarely suffer root rot because tap water does not contain much bacteria. Check this article for more on the difference between tap and rainwater and the effect on your plants. I kept basil cuttings for around 2 months with no sign of decay.
However, do not be fooled. Plants are living organisms, and they cannot survive on water only! The lack of nutrients and dissolved oxygen (if you do not change your water frequently) will cause your plant to wilt and die. There are two solutions to this problem.
- Replace the water once a week, providing the plant with fresh nutrients and oxygen.
- When the roots of a plant reach a half-inch in length, it is time to move them from the water to soil.
Soil roots come in all shapes and lengths, depending on the herb you are growing. Here is a summarized guide of the longer and shorter root systems:
- The longest roots are dill, coriander, and sage, which may need up to 61 cm (24 in) of soil to support enough vertical growth;
- The shortest roots belong to herbs like oregano, basil, and thyme can all manage with just 21 cm at most (8 in) of soil for their root systems.
Mint roots are unique in that they are a creeper type of plant— mint grows horizontally rather than vertically. For more on the topic, check the article on creeper roots. This creates a very shallow, broad root system. Mint also produces runners, or root-like extensions horizontally that then support vertical growth. Still, mint needs a decent amount, roughly 31 cm (12 in) of soil for its roots.
Not all plants and herbs can develop water roots. You can leave them in water as long as you want, and the only things that you will see are your plant slowly wilting.
I never managed to grow water roots from a dill or cilantro cutting. On the other hand, I am always successful with basil, lavender, mint, as they are very easy. Rosemary, on the other hand, is way harder to let develop water roots. In general, even with fresh cuttings, only half of them manage to root before rotting. Some herbs can only be propagated through cutting such as French tarragon, as mentioned by the University of Georgia.
Do not try to stimulate water roots formation with root hormones (check this article if you don’t know what root hormones are). Indeed, an experiment performed in the video below clearly shows that among 4 different types of waters solution, simple and plain tap water performed the best stimulating the highest root growth.
Before, I told you that you cannot plant uniquely in water. It was a (partial) lie. Indeed, there exists a technique (that got quite famous in recent years) by which you can grow a plant entirely in water (hence only through water roots) without moving to the soil. This is called hydroponic.
Keeping a plant in water reduces the maintenance required and is preferable to many aesthetics wise.
Hydroponic, as mentioned by VMD Agro, presents the following advantages:
- Water-rooted plants have narrower root systems, requiring less space;
- Because they are submerged, plants do not need to use energy to grow
root systems capable of absorbing enough water from the soil.
- Smaller root structure leads to more plant productivity, increasing yields by more than 150%.
- Because they have consistent access to nutrients, water, and sunlight at all times, hydroponic plants grow faster.
Hydroponics is hard and, despite having some experience, I do not recommend it or beginners. For more on hydroponics, watch the video below.
For at-home hydroponics supplies, one of the easiest systems is the VegyBox. You can check its current price on Amazon.
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