Hi Viviane,

The benefit to unglazed terracotta pots they are porous and allow moisture to evaporate through them. This makes it a little harder to overwater & might help avoid the associated problems.

Glazed pots, on the other hand, do NOT allow for evaporation. Glaze is essentially glass, which is non-porous & traps water in the pot, so any benefit from terracotta is lost. For all intents & purposes, glaze turns terracotta pots into plastic ones.... sorry.

The way to tell between terracotta (which is porous) and ceramic (which is not - again, the high-firing fuses the silica in the clay into a glassy substance) is to tap or flick the pot. Terracotta will sound dull & thumpy, while ceramic will kind of ring.

If you are so inclined.... and have the cash... and don't mind more slaving over pots.... one solution is to pot into terracotta & use the glazed pots as giant, beautiful saucers to catch your runoff water & disguise the "real" pot. I just read of someone who uses soda bottle lids as pot feet - what a good idea!

Otherwise, just keep track of your watering & be careful not to overwater! Good Luck!

Gravyboots

It's not so much whether the pot is glazed or unglazed, what's more important is whether the sides are gas-permeable, that is whether or not they allow water vapor and soil gasses to move through the pot walls.

Some will approach this issue from the perspective of grower convenience or the appearance of the container. I'll speak only from the perspective of what's better from the plant's perspective - for its health and growth.

Plastic and vitrified clay & other nonporous materials allow you to extend watering intervals - good for you - not so good for the plant. Plants like soils and pots that need frequent watering. Watering flushes gasses like CO2, methane, and sulfurous compounds from the soil. These gasses inhibit root function and metabolism, which inhibits growth and metabolism. Pots made of porous materials also allow these gasses to escape through the walls of the pot, and allows O2 into the pot.

You may notice an accumulation of salts building-up on the outside of these pots, but that salt has no affect on the level of salts in the soil inside the pot, so in fact they indicate a positive.

Practically speaking, I have a LOT of perfectly healthy plants in plastic and other nonporous materials. I do grow in very porous soils, which naturally contribute to free gas exchange by virtue of both their higher level of air porosity and because they need more frequent watering (which flushes salts AND soil gasses from the pot).

From the plant's perspective, or if they could talk, they would tell you they prefer something like terra cotta for their roots, but it's not the end of the world if you grow in plastic or other vitrified materials.

If you want to do an experiment, buy one of the baskets that are used to put pond plants in (they're like colanders). Put two identical plants side by side - one in the basket, the other in a plastic pot with the same volume of soil. Water as needed, not on a schedule - the plant in the basket will need more frequent watering and fertilizing. Make sure you water the plants thoroughly so plenty of water exits the soil each time. You'll be very surprised at the difference in growth and vitality between the plants.

That's the scoop from the perspective of plant health/growth/vitality.

I hope it was helpful.

Al

As long as salts are accumulating, there is gas exchange going on - yes? ;o) I've never seen a terra cotta pot that stopped accumulating salts & sometimes algae or moss, which couldn't grow w/o the moisture that they get through the container walls. BTW - it's a good time to point out that if the salt accumulations on the outside of the pot were harmful (soluble), algae and moss, sometimes lichen, would be unable to grow on the outside of the pot, but they do so quite nicely

I love the look - the patina of an old terra cotta pot. I have a lot of plants growing on for bonsai and a lot of houseplants. I try to put as many as I can in terra cotta, wood, or other containers that have gas permeable sides because the growth and vitality are noticeably better.

One of my growing benches. You can see how well-represented terra cotta is here. Subtract the plants that are already in bonsai pots (quite a few of which are in unglazed [air-porous] clay), and you'll see that most of the remaining plants are in terra cotta. The same is true of plants grown indoors. {{gwi:3279}}

Al

I use glazed pot to display plants in flower. I put the plant, with the original pot inside the glazed pot for display. Of course the glazed pot must be bigger. I use Styrofoam peanuts or a small plastic pot turned upside down to keep the original pot higher. Hard to explain...pots inside pots! I would not plant directly inside a glazed pot.

These orchids are all inside various glazed/unglazed pots.
{{gwi:72782}}

Jane

Hi Jane. Just curious to know why you wont plant directly inside a glazed pot?

Thanks

Freddie

I have orchids in glazed and unglazed and have never noticed any big difference in growth. As stated earlier glazed retains moisture longer than unglazed.

Technically you can grow anything in a glazed pot. As stated above, glazed does not let air flow and can hold too much moisture rotting the roots. If you are very careful about watering, you can grow in a glazed pot.

I don't recommend it because people tend to over-water. Orchids require a good air flow around their roots and will not grow well in a glazed pot unless it has slits or holes to allow good air circulation.

Jane

I had problems with glazed (and plastic) pots when i used bagged soils. Since i have been using the gritty mix all my problems are over. I planted a lot of Fuschia cuttings this spring and i used plastic, ceramic, terracotta and glazed terracotta pots. All of them are roughly the same height and i really dont see any growth difference between any of the pots. I sometimes water plants that i know are still damp inside and it still dont make no difference to them. I know now that the problem wasn't with the glaze (or plastic). It was with the soil.

Thanks

Freddie.

I don't see how they are going to breathe in a plastic pot dropped into a ceramic. Seems like you might as well just plant right in the ceramic. I don't see slits in the plastic.
JoJo

From the perspective of gas exchange in the root zone, all materials that are not gas permeable (glass, plastic, glazed ceramic) are pretty much created equal when it comes to assessing whether their impact on root health is positive or negative.

As Freddie points out, and as Jane's warning that 'you CAN grow in glazed pots if you're very careful about watering' illustrates, soil choice has a considerable impact on your margin for error. Fast soils = a very wide margin for watering errors and slow, water-retentive soils = a very narrow margin for error.

It just occurred to me to mention that if the margin for error is measured in lost potential, soils that support perched water can be said to offer no margin for error. I can say that because we know that optimizing growth requires that we reduce to the greatest degree possible all potential limiting factors. This means that for the plant to reach its full potential, everything has to be perfect - every factor that has the potential to limit growth must be eliminated, including air:water ratio issues in our soils.

We know this (perfection) is not something we can ever actually achieve, but neither is the perfect body something any of us will ever achieve, yet most of us strive to keep ours in good shape. So it can be with our plants. Some of us go to great lengths to stay as healthy as we can, others just 'let themselves go'. Some of us are willing to set aside some of our old habits (overeating, smoking, drinking, lack of exercise .....) to increase our potential for better health, some are not. That's the world we live in - reality.

When it comes to our plants, some are willing to cast off old habits and make an extra effort to do the things that ensure a better opportunity for our plants to grow to their potential, while some are perfectly happy to continue on the track they're on. That too, is life - reality.

If we consider WHY someone might admonish that we must be extra careful about how we water in glazed (or plastic or glass - all non-permeable) pots, we know it's directly related to the air:water holding capacity of the soil. If the soil holds too much water/not enough air, and supports a significant PWT, it's bad in ANY pot - even those that are highly permeable, but they are particularly hard on plants in impermeable pots.

If you switch your focus now, to a soil that ISN'T heavy and water retentive, one that is full of air even when it's holding as much water as it can possibly hold, it's easy to see that there is no need to work around or worry about wet/soggy soils in impermeable pots. (See Freddie's post immediately above.) Soils that don't support perched water (or VERY little), have excellent gas exchange and plenty of air porosity - even in plastic or glazed containers; so all of a sudden and by simply shifting focus to a soil that holds more air/less water, the need to issue the warning that you CAN grow in pots with impermeable sides if you're very careful about watering, no longer applies.

The message is, it's to our plants' advantage to use pot/soil combinations that return the soil to a DAMP, air-filled condition as quickly after watering as possible. These are the soil conditions most conducive to root health. The top of the plant that we all like to look at is a part of the same organism as the roots, and cannot be healthy unless the roots are healthy.

Al

I'm with Al on this one... I prefer the permeable qualities of unglazed terra cotta, and I notice that my plants prefer it, too. I try to use unglazed terra cotta clay pots as often as I can... although, I do have a few plants in plastic pots.

Since I, too, use a soil that's more aerated and free draining, the few plants I have in plastic pots are still able to function normally.

Personally, I like the look of the aged, unglazed clay pots much better than the plastic or ceramic pots, but if the medium inside allows the roots to function well, it shouldn't really matter which pots you choose. With a good aerated, fast draining medium, it becomes more of an aesthetic choice.

"With a good aerated, fast draining medium, it becomes more of an aesthetic choice. "

AMEN to that jodic. When i discovered the gritty mix i started snuffing out all my old pots. Now matter what it was i planted in it. The coming winter will be the big test but judging by the results so far i (and my plant children) am very much ready to take it on.

I JUST WISH I KNEW THIS 20 YEARS AGO !!!

Freddie.

Hi everyone!
There's some great reading here!
Al~ thank you for the great post! Many will learn from it.

In the past, I always used plastic. I have many containers in the yard. And the few plants in the house, I just figured it would work O.K., and cheaper, considering how many I needed.

After joining GW and learning terra cotta is better for the plants, i've been slowly changing them all over. I see a big difference in my plants.

Like Al~ I love the look a well used terra cotta! They have character!

I have a few "cute" glazed containers, that I will continue to use, and just keep an eye on their water needs.

JoJo

"I JUST WISH I KNEW THIS 20 YEARS AGO !!!"

I do, too, Freddie... I do, too! I could have done so much more, and come so much farther in growing... but, better late than never, as they say!

The gardening industry doesn't offer much in the way of variety, mainly because that would defeat their purpose... a larger profit line. The more consumers buy, the larger that profit. And so, it doesn't do them any good to supply us with mediums or information that allow us to get longer life from our containerized plants and growing endeavors.

But, we have generous teachers, like Al, who work tirelessly to explain the basic science of plants and growing, and offer us alternative mediums that we can easily build, ourselves.

The addition of a better medium to unglazed clay containers makes for as close to perfect as one can get when working with the confined space of containers... and as we know, growing in the ground is quite different, as we are in control of moisture and nutrition and other factors when growing in pots.

I think the bottom line is finding a medium that allows for the highest functionality of a plants' roots... after that, the container can be whatever you prefer as the gardener.

Jane, do you find those beautiful containers locally, or do you have a favorite on-line vendor that you will share? They are really pretty. I'd use them for my indoor plants, in a heartbeat.

I grow all my plants in plastic, orchids and dirt plants. I have no watering issues. I do not like clay pots except for display or weight.

Thanks, Rhizo I find pots in various places. I'm always on the look out. Last week I found a few ceramic pots at TJMax (of all places). Home Goods have some occasionally. I have a collection of glazed and unglazed which I like for displaying orchids. Some have no drain holes and have to be drilled.

A couple, in the photo are actually painted metal.

Jane

I use both and do not have a problem. If I am using the plant in a common area for decorative purpose I use glazed. It all comes down to knowing how to not over water. I have not killed a plant in a glazed pot.

If I was a nursery or just liked to grow thousands of plants lined up like little soldiers then terracotta would be fine. But...A terracotta pot would not look good in my living room. LOL

My Amaryllis is planted in a glazed ceramic pot. I've been advised the reason I'm having trouble acclimating the plant to mild outdoor temps is the black pot is getting too hot and the roots are unhappy (one leaf is consistently wilting in 80 degree temps in a climate that's about to get up to 100-110).

Here's my solution to the problem. I want to sit the plant in a water bath. That way the pot can't get too hot. But what I don't know is if I can trust the pot not to absorb water. It came in a kit without drainage holes. Burying the pot is not an option.

{{gwi:72784}}

If your pot doesn't have a hole, the odds are the reason you're seeing wilting is a soggy soil is impairing root function. A lack of sufficient oxygen is inhibiting the plant's ability to maintain turgidity (water pressure), so the plant wilts.

If the pot is simply glazed terra-cotta, you may or may not be able to get away with your plan. It's more likely workable if the pot is highly vitrified, but if it came in a kit, it's probably not. You might consider double-potting. Put your pot inside of a larger pot and fill around your pot with something porous & absorbent. If you keep the filler material damp, it will cool your pot as the water evaporates.

Amaryllis doesn't tolerate wet feet well at all. I would drill a hole in the pot ore repot into another pot with a hole. If that sounds like a plant to you, let me know & I'll help you with a drill bit selection and some instructions.

Al

Thanks a lot, Al. I aerated the soil carefully with a straw. I'm going to move the plant to less sun, continue with extremely careful watering and re-pot in the fall.

GrowSis

OK. I'm ready to drill but I need to do this essentially for free. I have regular drill bits. Will masonry work (cheap)? Or do I need ceramic?

If your pot is glazed terra cotta, and you're willing to sacrifice a speed drill bit that's 1/4" or larger, you can probably get through it. A masonry bit will also work for terra cotta, but it's a poor choice for vitrified (hard) material.

Al

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