How can ‘over-potting’ be a thing when plants grow straight from the Earth’s surface with infinite amounts of soil available?
In: 1858
There is “infinite soil,” but there aren’t infinite nutrients for the plants *within* that soil. Too many plants drawing nutrients from the soil is like three people drinking from straws out of a single drink. Eventually the drink is empty and no one is particularly satisfied.
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‘Over-potting’ isn’t about ‘too much soil’. It specifically refers to the relationship between a plants ability to uptake water, and the soil it’s planting in, ability to dry out.
Most plants require a wet/dry cycle to properly grow. If you put a teeny-tiny plant in a big giant pot and water the pot until it’s entirely saturated, the amount of soil in the pot will take longer to dry out than the plant’s ability to uptake the water. Thus, the plant can literally ‘drown’ because in addition to water, their roots require oxygen, and they die.
Plants in the ground have this problem also….it’s just that there’s usually plenty of other plants competing for that water and they deal with it.
>LI5: How can ‘over-potting’ be a thing when plants grow straight from the Earth’s surface with infinite amounts of soil available?
Because there isn’t “infinite soil” available. Many plants are specialized to grow in very thin, nutrient-poor soils and will rot or suffer other ill-effects in soil they’re not adapted for.
A lot of people kill Blueberries for example (a plant that grows on thin, sandy soil or even nearly bare rock) by planting them in a rich, nutrient-rich soil. They grow on barrens with pines and oaks similarly adapted for that habitat.
Moisture has a profound effect too, a big pot full of spongy soil will hold onto a lot more water than a plant can use and will cause root rot. I grow cacti in the Northeast were it is very humid and I have to keep even large cacti in comparatively tiny pots to ensure they dry out as quick as possible.
Besides what other people have said, I think you might be very surprised at how shallow and not infinite soil is in many places.
“Overpotting” is also a bit of a oversimplification. Just because a pot seems too big or too small doesn’t mean it will do inherently poorly or well. A large pot that’s well-draining with lots of perlite, sand, bark, and other media that’s poor at retaining water can dry out faster than a much smaller pot with rich soil with like vermiculite and packed mosses. How quickly a pot dries out is all about the pot shape, the media, the pot material, how you watered the plant, how wet tolerant your plant is, how much water the plant uses, temperature, humidity, etc. One of the best things to learn about houseplant care is learning how to adjust your potting and watering to fit your lifestyle and your plant’s needs.
In the ground, water can drain away in every direction. In a pot, it can only drain out through a small hole in the bottom. Moisture is retained much more easily in a pot, especially in the dense, rich potting soil sold by most nurseries, leading to rot.
The nutrients required for flowers are the same as roots. For perennial plants it is usually more advantageous for survival to spread roots than to flower. Roots take up a wider area for shoots to come up if the plant above the ground is injured.
Once the roots are constrained those nutrients can’t be used to make more roots, so it us used in flowering, fruiting, and seeding.
The other thing that tells plants to flower is the shortening of days. Constraining/rootbounding a plant convinces it to flower early.
Example: if you repot a primrose into a much bigger pot it will take a year or more to fully flower. If it is repotted into a pot of the same size it will flower within a couple months. The same is true for African violets, Christmas cactuses and countless more.
Edit: Why would someone repot a plant into a similar or slightly large pot? Eventually the roots get so dense that most of soil is gone and then the plant can only absorb nutrients through slow drip hydroponics. Sound fancy and scientific? It is, and very tempermental and difficult to maintain.
Infinite soil means infinitely deep drainage for excess water to drain away.
Not so in a pot: a layer at the bottom stays completely saturated in a phenomenon known as the perched water table. (Note that adding a “drainage layer” of bigger rocks does not help this–it just means the perched water table is higher up in the medium.)
In a very big pot, the amount of moisture a plant can intake relative to the pot size is miniscule, so the roots stay wetter longer and die faster.
Note that pots that are very wide have worse drainage than pots of the same volume that are very tall. That’s why all tree nurseries use tall pots with good drainage holes. You can try this out for yourself with a flat container. Water it thoroughly, then wait ten minutes. Now tip it up on its side, and way more water will flow out.
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