Pot Size

I have recently been collecting houseplants and I have one question I can't seem to find the answer for. How do I find out how large a pot the full-grown plant, any plant, will require? I see spacing information in the database, but I'm not seeing pot size. Should I base total pot size on spacing?

You need a pot that will the roots will fit in with some room to grow, but not a lot. I have read that "rule of thumb" is to put a plant in a pot that is 1" wider than the rootball. Keep in mind, some plants do better with less space to grow and some like more.

If growth is the measure of 'better', all plants do better with plenty of room to grow .... the larger the pot, the better. However, your/our choice of soil often tosses a wrench into the cogs and limits your ability to use large soil volumes and large pots for smaller plants because of the danger of excess water retention causing root rot. As the size of the particulates you choose as the primary fraction of your soil increases, so does the volume of the pot/soil combination you can use w/o problems. As an illustration, think of a very large container full of BBs. Is there any danger of a plant being over-potted in a soil made of BB-size particles? The answer is "No". Now think of a peat, compost, or coir-based soil. Is there danger of over-potting? The answer is assuredly "Yes".

I wrote the following a while back. There may be extra information in it, but it discusses the relationship between soil type and pot size in a little more detail:

WAIT! WAIT! Call on me for this one! (waving hand) ;o)

How large a container needs to be, or CAN be, and how much soil a planting needs/will tolerate before drainage & saturation is an issue depends on the 3-way relationship between plant mass, container size, and soil type. We often concern ourselves with "over-potting" (using a container that is too large), but "over-potting" is a term that arises from a lack of basic knowledge about the 3-way relationship noted, which should logically determine appropriate container size(s).

It's often parroted that you should only move up one size in containers when "potting-up". The reasoning is the soil will remain wet too long and cause root rot issues, but it is the size/mass of the material and soil type/composition that determines both the upper & lower limits of appropriate container size - not consecutive volume progression.

Plants grown in slow soils need to be grown in containers with smaller soil volumes so that the plant can use water quickly, allowing air to return to the soil. This (smaller soil volumes) and the root constriction that accompanies it will cause plants to extend and gain o/a mass much more slowly - a bane if rapid growth is the goal - a boon if growth restriction and a compact plant are what you have you sights set on.

Conversely, rampant growth can be had by growing in very large containers and in very fast soils where frequent watering and fertilizing is required - so it's not that plants rebel at being potted into very large containers or volumes of soil per se, but rather, they rebel at being potted into very large containers with a large volume of soil that is too slow and water-retentive.

We know that there is an inverse relationship between soil particle size and the height of the PWT in containers (PWT = perched water table. If you don't understand this term, please find more about it here):
http://davesgarden.com/community/forums/t/1073399/
As particle size increases, the height of the PWT decreases, until at about a particle size of just under 1/8 inch, soils will no longer hold perched water. If there is no perched water, the soil is ALWAYS well aerated, even when the soil is at container capacity (saturated).

So, if you aim for a soil composed primarily of particles larger than 3/32", there is no upper limit to container size, regardless of the size of the plant or the root mass. The lower size limit will be determined by the soil volume's ability to furnish water enough to sustain the plant between irrigations." You can grow a very small plant in a very large container if the soil holds little or no perched water.

Shifting to your last question about 'drainage layers'. Drainage layers do not promote drainage. They simply chance the location of the perched water in a container from the bottom of the container to just above ('perched' on top of) the 'drainage' layer. To some degree they can be effective. They reduce the volume of soil needed to fill the container, which has an affect on the o/a volume of water in the container (less soil holds less water). If, however, a soil holds 3" of perched water, and you use 6" of drainage material in the bottom of the pot, you will have 6" of well-aerated drainage material with a 3" layer of saturated soil immediately above it that will rot roots just as effectively as if it was at the pot's bottom.

It's MUCH better to NOT rely on an ineffective drainage layer - to use a mix that remains well-aerated always, and drains well - a homogeneous medium from bottom to top of the container.

Al

Thank you both.

Tapla, I'm using Hydroton rather than soil. I don't like soil in the house (nor have I ever been successful with anything other than aloe in soil) so I decided to go with hydroculture. If I understand your explanation correctly, there is no upper limit to pot size for my plants because of the nature of the Hydroton. My only disadvantage that I see to putting a little plant in a big pot would be I would lose more water to evaporation, which isn't necessarily a bad thing, particularly for plants that like high humidity at the foliage.

However, I assume my plants will have a mature size. I do not want to have to "pot up", so I would rather put each of my plants in a pot that will be ideal for that plant's mature size right from the start. Often, when I purchase a plant, I have no idea how big it can get. How do I found out what size pot it would need if it were at its expected mature size?

I don't mind having too big a pot (aesthetically speaking) to start with. I just don't want to have to transfer to a larger pot later.

In hydroculture, there would be no upper limit to pot size. Plants adapt to hydroculture by forming roots that are considerably different than the roots in solid media. Parenchyma cells primarily make up the root cortex of plants grown in soils or other solid media that are well aerated, but a different type of cell groupings called aerenchyma forms in roots that are subject to periods of anoxia (w/o air) when they are submerged. Aerenchyma tissue has elongated air channels that allow the oxygen roots need for function/metabolism/growth to diffuse (move) from the foliage to the roots. This difference in tissue is why rooting plants in water you will eventually move to soil is not as productive as rooting in a well-aerated solid medium.

Plants don't really have a mature size. We, like plants, go through several life stages - embryonic, juvenile, adolescent (intermediate in plants), and sexually mature - all stages roughly shared by humans and plants. Where we vary greatly is in the way our cells age. Plants must grow to live. A plant that is not growing is dying, so your plants will always be growing, even after reaching a 'mature' size. Depending on what types of plants you are tending, you can keep most them at the size you prefer by judicious pruning of both the top and roots. Call it hydro-bonsai, if you would like to coin a term. ;o)

Don't be concerned about having to "pot-up" plants in hydroculture - it's no big deal. Just be sure you select pots w/o constrictions at the throat or reverse tapers, so they will allow you to easily lift the plant from the pot for root pruning.

Al

Thanks a bunch, tapla. You have been most helpful.

Hydro-bonsai!

Tapla, I have a blog documenting my trip into hydroculture. I would like to add some additional educational type information to share with others who are also new to the experience. Would you mind if I quoted your comments here on my blog?

http://hydrocassie.wordpress.com

Go ahead - feel free. I appreciate your being considerate enough to ask permission.

Al