How do you know what size planter to use?

If a plant says it grows to 15" tall and 5-6" wide, how do I know what size a planter I should use? I think depth is the more difficult thing to figure out.


Also, when they say "4-inch pot" or "10-inch pot", is that describing the diameter of the rim or the base or the height of the pot?

It is the diameter of the top. And when you have to 'move up' a pot, use 2 inches as your guide. Example: If in a 4 inch pot, repot into 6 inch pot. The reason is the roots will fill this in fairly fast, allowing for quick top growth and flowering.
Depth is determined by how deep of a root ball (or taproot in tree cases) of your plant will have. Since these are all different depending upon the plant, it is good to know what kind of roots your plant has. I have also found this to be one of the most difficult things to research about a plant. A lot of looking at them firsthand through the years gives me some experience, but this doesn't help at all with plants I am unfamiliar with, as seems to be your situation. What kind of a plant do you have that you are trying to determine this?

I'll give you an example of what I mean. A loquat (Japanese plum) is a tree that will not develop a long taproot, so when I pot one up I don't have to use a super deep pot. It's roots tend to spread across the surface area.
But if I am potting up a mamey tree, this does have a taproot and I need a very deep pot, and must be careful to re-pot as soon as it reaches the bottom, lest I could damage the tree and stunt it's growth.
In the case of houseplants, you rarely will have this problem and can usually use the basic pots that are in demand without any issues.

This message was edited Nov 19, 2011 3:49 PM

yeah, it doesnt really matter how tall/wide the plant grows, but instead what the actual plant is. when youre buying the plants remember that the pot is its home for the roots. curios, what plants were you going to pot up?

Here is something I wrote about choosing a pot size a while ago:

How large a container can or should be, depends on the relationship between the mass of the plant material you are working with and your choice of soil. 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 a basic understanding about the relationship we will look at, which logically determines appropriate container size.

It's often parroted that you should only move up one container size when "potting-up". The reasoning is, that when potting up to a container more than one size larger, the soil will remain wet too long and cause root rot issues, but it is the size/mass of the plant material you are working with, and the physical properties of the soil you choose that determines both the upper & lower limits of appropriate container size - not a formulaic upward progression of container sizes. In many cases, after root pruning a plant, it may even be appropriate to step down a container size or two, but as you will see, that also depends on the physical properties of the soil you choose.

Plants grown in slow (slow-draining/water-retentive) 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 before root issues beyond impaired root function/metabolism become a limiting factor. We know that the anaerobic (airless) conditions that accompany soggy soils quickly kill fine roots and impair root function/metabolism. We also know smaller soil volumes and the root constriction that accompany them cause plants to both extend branches 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 your 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 per se, but rather, they rebel at being potted into very large containers with a soil that is too slow and water-retentive. This is a key point.

We know that there is an inverse relationship between soil particle size and the height of the perched water table (PWT) in containers. 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 (fully saturated).

So, if you aim for a soil (like the gritty mix) composed primarily of particles larger than 1/16", there is no upper limit to container size, other than what you can practically manage. The lower size limit will be determined by the soil volume's ability to allow room for roots to 'run' and to furnish water enough to sustain the plant between irrigations. Bearing heavily on this ability is the ratio of fine roots to coarse roots. It takes a minimum amount of fine rootage to support the canopy under high water demand. If the container is full of large roots, there may not be room for a sufficient volume of the fine roots that do all the water/nutrient delivery work and the coarse roots, too. You can grow a very large plant in a very small container if the roots have been well managed and the lion's share of the rootage is fine. You can also grow very small plants, even seedlings, in very large containers if the soil is fast (free-draining and well-aerated) enough that the soil holds no, or very little perched water.

I have just offered clear illustration that the oft repeated advice to 'only pot up one size at a time', only applies when using heavy, water-retentive soils. Those using well-aerated soils are not bound by the same restrictions.

We needn't be at all concerned about providing a container deep enough to accommodate a plant's tap root. First, most plants we grow would have been vegetatively cloned and don't have one anyway, and second, as soon as the tap root is truncated, it can't extend. Plants that have a tendency toward long tap roots are easily managed during a repotting (as opposed to potting up), which includes regular root maintenance.

Also, plants that tend to have a shallow root system in situ, aren't necessarily genetically predisposed to such. Plants like azalea, rhododendron, boxwood, and others with very shallow fibrous root systems, will happily colonize the entire soil mass in even the deepest of pots if the grower uses a soil with good aeration.

Finally, and FWIW, there is a very good guideline in place that allows you to determine when to repot or pot up. You can pot up w/o negatively impacting growth IF you pot up BEFORE the root/soil mass reaches a point where the roots and soil can be lifted from the pot intact. If at any time the root system is allowed to become congested beyond that pivotal point, growth and vitality are almost certain to be compromised for the life of the plant - even if you plant it out. Left to progress to some degree of congestion beyond the pivotal point mentioned, the plant would need root pruning to negate the effects of the congested root mass.



Al

There are a few new ones I'm looking for seeds for.
Catananche caerulea (Cupid's dart)
Campanula persicifolia (Bellflower)
gentiana sino-ornata (4-5" tall, spreads out)
nigella damascena (Love-in-a-Mist, annual, has a taproot)
Sea Holly (long taproot)
Sweet Pea (annual)

The nigella is the one that's 15" by 5-6" and I was hoping to get it into a smaller planter. For the Sea Holly I was going to buy a root (or whatever you call the started plant) online.

I have a 6" wide x 6" tall planter, kinda narrow ./, and a 7.5" x 6.5" wide |_| one.
The rest I will have to shop for.

Oh I have 2 of those tiny 4" pots that I never have any use for.

Shoot, I just realized this is in Houseplants intead of Beginner Gardening. I don't suppose I can move it can I?

This message was edited Nov 19, 2011 3:52 PM

Where'd everybody go?

.... probably waiting to field any questions you might have.

Al

Just hoping to get some thoughts on what containers I should use for the plants.

I think I'll put the gentians in a long window planter. But not sure about the other 2 planters or what I should buy for the rest.

It ALL depends on the plant. An African violet for example needs a shallow, small pot. 1/3rd the leaf spread. They have VERY small root systems.

I can understand why the recommendation for a pot for AVs, 1/3 the size of the leaf spread if it's for aesthetic reasons - because it looks nice; but, can anyone explain why a shallow pot (much more difficult to grow in than a deeper pot) is 'better', without basing the recommendation on an assumption about what type of soil is being used? I'll say in advance that I'm setting up a trap to hopefully start a conversation (as opposed to an argument) that goes deeper into the whys/wherefores about what determines appropriate choice of pot size. Rereading my offering of 11/19 will give some indication of the direction I'm heading. You CAN grow the tiniest slip of an AV in 10 gallons of soil in a 36" deep pot, if the soil holds little or no perched water; and you can expect better growth and vitality than if the same plant was situated in a pot that more closely follows the guidelines in Tommy's post.

Al

Good Morning Al,
I have a mini-chimera (type of AV). Thanks to you I am growing all of my houseplants (except the chimera) in the gritty mix and they are very robust.
Would growing the mini-chimera in the gritty mix in a larger pot (a 4" pot vs. a 2.5" pot) change the plants form from a "mini" to a "maxi"? What are your thoughts?

Thanks,
Linda

p.s. Happy Thanksgiving to Everyone !!!

Happy Thanksgiving to you too, Linda - and to everyone else out there in Daveland. ;-)

When we're discussing plant aberrations like true dwarfs, chimeras, sports ...... we need to look to the plant's genetic predisposition. That doesn't mean though, that things cultural can't have a very significant impact on growth habit - it can. For example, once I get some ramification (branch/leaf density) built into my bonsai trees, and the effects of a small soil volume are added in, I'm able to reduce leaf size to only a fraction of the size they might be on a plant growing in the ground. So in the technical sense, we know that cultural conditions have no real effect on determining whether or not a plant is a 'mini' or a 'maxi', but in the practical sense, we know that growing a mini in a small pot will employ the stress associated with small soil volumes to help keep the mini MORE mini than if it was grown in a soil volume that allowed plenty of room for roots to run.

If plants truly did grow better in small soil volumes, Mother Nature would have arranged for their roots to grow in tight little knots directly under the stems. Instead, she designed plants so their roots would spread and take advantage of moisture and nutrients over a wider area/volume of soil. We can sometimes employ the stress associated with small soil volumes to keep plants compact, or even to produce more blooms, but it's important to understand that we do this to please the eye of the grower. Stress is not good for a plant, no matter how you dice it. You can achieve best growth and vitality by growing in large volumes of soils that allow roots plenty of room to run. It's only when you start to introduce the negative effects of soils too water retentive to ALLOW you to provide the larger volumes of soil that produces best growth and vitality (for fear of the growth of the fungaluglies that cause root rot) that 'over-potting' becomes a consideration.

Al

Al,

Thanks for the insight. In the spring, I may do a little experiment and put my chimera in the gritty mix and a larger pot. I think some adventure & experimentation will benefit my skills as a "wannabe" master green thumb.

Now go gobble a gobbler!!

Linda

nevermind i guess :(

Blake (said in a kind way) - I didn't reply further because I thought I explained what determines container size very well, just a little up the thread. Without some sort of feel for the type of soil you are using and how large the plant mass and root mass are, no one can offer advice that is on the favorable side of meaningful.

If you're using a soil that holds little or no perched water, there is no upper limit to pot size. If you're using a heavy, water retentive soil (like Miracle-Gro, Jungle Grow, Black Gold and others using peat as the primary fraction of the soil), you should start with a small pot and pot up BEFORE the soil/root mass can be lifted from the container intact. Whenever you get to the point where roots are congested beyond that point, you should do a full repot and again use your soil choice to guide you to whatever pot size is appropriate for whatever soil you're using ant the size of the plant you're working with.

I'm a very strong advocate of using very well aerated and fast draining soils, simply because they remove all this angst from the shoulders of the hobby grower.

Linda - the quickest way to a green thumb has far less to do with experience than it does with knowledge. When you learn all you can, and then let your practical experience validate your knowledge, you'll blow right past those that rely on experience only as their teacher. The reason for that is, w/o knowledge we make up science to fit what we think we are seeing. IOW, we jump to a LOT of erroneous conclusions that a little knowledge would immediately have invalidated. Instead of properly questioning our observations and perceptions because we lack the knowledge needed to see they don't fit with what we know of science, they become dogma and a part of what we have "learned". It's often easier for beginners to reach "green thumb" status than gardeners with many years of experience; that, because it's more difficult to 'unlearn' the long-held beliefs before you get the facts straight than it is for a beginning gardener to simply get it right from the outset.

Al

I haven't bought the soil yet, I'll probably buy it with the new planters. I usually get soil that's got lots of organic matter.. which might be pointless because I sterilize it with boiling water before using it. I had a horrible war with fungus gnats last year from my first bag of Scott's soil.

So I'll probably put all new plants in the new, sterilized soil (except one that requires INfertile soil).

I'm going to have to get a couple of planters so I'll probably get soil at the same time. So I should stay away from soil that has a lot of peat then?

I don't know what you mean when you said "you should start with a small pot and pot up BEFORE the soil/root mass can be lifted from the container intact". Doesn't that damage the plant?

I think you could benefit significantly if you read the thread I'm going to link you to and gain an understanding of what's in it. Growing doesn't have to be difficult, but the road to proficiency is long if you rely only on your errors as your teacher. Understanding a few basic concepts at the beginning of your growing endeavors can quickly improve your skillset and reduce most of the frustration associated with sort of starting from scratch. Some of the basics outlined in the thread that can be understood in less than an hour, might take you years to understand if you approach things on a trial and error basis.

See what you think ..... and please join in the discussion if you like. You'll discover that not only is working on the roots REQUIRED for long term growth/vitality, but that it also has a rejuvenating effect on your plants.

http://davesgarden.com/community/forums/t/1226030/

Al

WOW.

I'm sure that is full of good info for gardening experts, but I was looking for a rule of thumb.

I've spent tens of hours in the last year learning about gardening and I'm pretty much spent. I just don't have it in me to put more work into a few plants on my balcony. It's all so exhausting and out of control. If they die, they die.

The main rule of thumb regarding the endeavor of (container) gardening, which also includes tending houseplants, is much like that of any other undertaking ..... what you get out of the experience is closely related to what you put into it. Most hobbies require a large measure of enthusiasm for that hobby to help you get by the rocky places, with container gardening being no exception. Any effort to learn you decide to make would be well spent, and will assuredly help you advance much more rapidly than you ever could by adopting a laissez faire approach; but that, of course, is solely up to you. I wish you well.

Al

Hey Blake, from one beginner to another, here's my version of what I've learned so far.

Commercial potting soils retain too much water and lead to common plant diseases and plant loss. Well-draining soil is important for container gardening. An easy potting mix is 5 parts pine bark fines (not the big nuggets), 1 part perlite, and 1 part peat moss. It doesn't last as long as the other mix that Al recommends, but these are easier ingredients to find.

When you use a commercial soil mix, you have to be very careful about pot size, because the roots can drown or cause a lot of other issues with air/water uptake. When you use a well-draining potting mix that's not so peat-heavy, and take care of the roots by regular root-pruning, then you don't have to worry so much about the pot size. It becomes a non-issue.

If you're not interested in making your own potting mixture and you want to just use the commercial mix, then you have to be very careful about the pot size. That's why Al was trying to steer you away from using the commercial mix. I think the rule of thumb (when using typical soil) is to increase by one pot size at a time. So if you bought the plant in a 4-inch container, go up to the next biggest size, and not to the "maximum" size of the plant. Once again, the container size becomes a non-issue once you change the soil structure to something better draining.

I am growing all but one of these from seed. What I have done is put seedlings directly in the final planter after they get their first set of true leaves.

I don't have multiple sizes of pots, and don't have the room to store extra pots to keep potting up.

I think I'll just try to find pots that are big enough (random guess), and potting soil that's low in peat. I didn't think there was this much to it. For the 5-10 plants I grow, it's really not cost-effective to put more energy into it.

First year of gardening took all I had. So many regrets, so much work I should never have had to deal with. Now, it's either easy or I quit gardening altogether.

Tell me about it, Blake! I haven't added up the cost of the plants I lost this year but I imagine it's in the hundreds :-( The good thing is that I know exactly what I did wrong and I won't make the same mistakes again.

I've never grown anything from seed, but I think experienced seed growers will say not to put seedlings directly in the final planter. It's going to be very very difficult for those seeds to survive that environment. Did you keep any little plastic plant containers from when you bought your plants earlier this year? Maybe you could start your seeds there and then transplant later.

You might get more specific help about growing from seed from the seed germination forum.
http://davesgarden.com/community/forums/f/germination/all/

I haven't bought plants before, everything was from seed so I have no little containers. I keep things like Dairy Queen Sundae lids for seed starting. I usually start them in tupperware or some small container like that, and once they germinate to 2 true leaves, I move them into the final container.

That's why it's hard to tell what size since I only have a measurement of how tall the plant can grow.