Shop Products
Houzz Logo Print
greentoe357

biology of drying out roots

greentoe357
10 years ago

An experienced hoya grower wrote this here (https://www.facebook.com/notes/hoyas-101/some-basic-notes-on-growing-hoyas/270673633089804, you need to be on facebook and a member of her "HOYAS 101+" group - ask and she'll add you):

"Clay pots are lovely...but there is a big drawback to them: when they dry out they kill the fine sensitive roots that are clinging to them on the inside. Then watering can cause those dead roots to rot and the plant will decline. Plastic pots, I find, are much better...or ceramic pots that are glazed on the inside."

Some of this does not make intuitive sense to my non-professional /non-experienced self, and I want to better understand what happens if the mix and roots are allowed to dry out and then are watered again.

I get that fine roots cling to unglazed clay (just like they cling to bark, hydroton and some other types of ingredients). Assuming no drying out, giving the roots something full of both air and water to cling to like that is a good thing, right? I also get, of course, that roots may die, and fine roots die first, when the medium is too dry. But my understanding is that this and subsequent dead root rot happens when the medium is re-wetted whether the pot is clay, plastic, glazed or unglazed. So, it does not seem like a disadvantage of unglazed clay. What am I not seeing?

Also, the dead root matter rotting - how much of a real problem is that? If only the fine short almost invisible hair roots die during accidental short periods of dryness, then there is not THAT much organic matter to rot. Some of it will just crumble and see itself out through the drain holes before rotting, I assume. (another benefit or coarse fast draining mix). This is not to say that death of fine roots is not a problem! - I understand it is, because those roots are primarily the ones doing the work of sucking the moisture and the nutrients in.

On clay pots, you will never get a consensus, and we should not even try. Their porosity works well for growers, watering schedules, mixes, climates and plants that want/need faster drying out or better gas exchange. But of course they would not work well for arid climates, forgetful waterers and fast-draining mixes etc.

But biology of what happens in a pot when the mix is dried out and re-watered is interesting to me. Thx.

This post was edited by greentoe357 on Mon, Jan 27, 14 at 9:39

Comments (4)

  • tapla (mid-Michigan, USDA z5b-6a)
    10 years ago

    Plastic pots are little different than clay pots in that regard. When most soils start to dry down, they shrink away from the edges of the pot, which allows air circulation between the pot and soil, which increases the rate of desiccation at the outside of the root mass.

    Most importantly though, I have hundreds of plants of all stripes in terra cotta containers, and they are in these pots because they produce extremely healthy root systems. The key to healthy roots though, isn't so much the choice of pot as it is the choice of soil. No matter how you slice it, soils that support lots of excess water in that soggy layer at the bottom are more difficult to grow in. Fortunately, clay pots are a significant plus when using water-retentive soils because the increase in soil gas exchange they offer also tends to dry soils out faster. This may cause a little more work on the part of the grower, but from the plant's perspective, soils that need watering more frequently offer better potential for growth and health.

    I NEVER have the die-off of roots at the perimeter of the pot you mentioned above when using clay - even given the very open (fast-draining) soils I use. Dozens of pictures I've posted of very healthy root systems of plants I grow in low-fired clay containers should serve as clear illustration that root dieback at the outer limits of the root balls is nothing to be concerned about.

    Additionally, death and regeneration of roots in containers is an ongoing process. When roots break down in plastic containers, gas exchange is limited by the container walls. The finer the soil - the greater this problem becomes. Plastic pots are excellent at trapping CO2 in the root zone, along with other gases produced during breakdown of organic matter. Clay pots are much better at allowing these gasses to escape - again, especially helpful when using fine soils that tend toward supporting more anaerobic activity.

    Even if clay pots did kill roots at the pot perimeter, it still wouldn't be an issue. All we need to do is look to growing bags, root-trapper and similar pots to see that dead roots are never much of an issue where there is good air circulation/gas exchange. Where they ARE a problem is in plastic pots, especially when combined with heavy (water-retentive) soils.

    To get a consensus on clay vs plastic, you need to look at the problem from only one perspective at a time. Plastic has it's advantages for the grower, but from the plant's perspective, they'd MUCH rather be in a clay pot. As long as the grower holds up his/her end, clay pots will outperform plastic every time.

    Al

  • greentoe357
    Original Author
    10 years ago

    Thanks, Al. Makes sense.

  • teisa
    10 years ago

    Good information Al! Got my brain awake better than coffee!

  • tapla (mid-Michigan, USDA z5b-6a)
    10 years ago

    {{gwi:2595}} Al

    Thanks!

Sponsored
Grow Landscapes
Average rating: 4.5 out of 5 stars8 Reviews
Planning Your Outdoor Space in Loundon County?