I'm trying to understand more about sizing containers.

I get that you are supposed to not plant in too big a pot at first, but gradually increase with multiple repottings.

But, how do I know which pot size to go to next?

For instance, I just got 2 fragaria vescas that are in 4" pots. Do I repot them in 6" or 8"? And if their full grown size is about 9-12 inches wide, how big should the final pot be?

I also have a salvia 'fancy dancer' that came in a 4" pot. I did repot it into a 9" pot already and it's happy. As it will grow to be 18-24"x18-24", what would be the final pot size needed?

I just bought two 22.24x13.04 49 quart barrel pots for $20 each. The other colors of the same pot and size were $60+ and the tags on these pots show those measurements but then have another descriptor showin them as being 1.5 gallon and fitting a plant with a 9-1/2" diameter. I think they messed up the labels and I got a great deal!

But I'm looking at these pots wondering what will fit in them? Will the salvia be a good fit? Or something bigger?

I also have a salvia x jamensis 'sierra san antonio' to pot. It is currently in a 3" pot. What size container next? And at an adult size of 2-3' x 2-4', will it be a good candiate for one of my big barrel pots?

OK. This is what I did:

1 fragaria vesca in the 6" pot
1 fragaria vesca in the 13" hanging pot (that is sitting on a cement pier block)
1 salvia x jamensis in the 10" pot

Except for the giant pots, I am out of pots. Have to start looking to get more. I guess I should get more in the 10-15" size range as I'm sure the fragaria vesca will outgrow the 6" pot.

I also did some reading and everything says to go with a pot about 2" bigger than the root ball. But how do you know how big your root ball is until you unpot the plant? Or do you assume it's the size of the existing pot?

Yes to your last question. However, lots of variables. I'm going to address outdoor plants like your salvias, not indoor tropicals.

The "rules" about pot sizes have evolved in large part because of the prevalence of peat-heavy potting mixes. If you put a small plant in a large pot and saturate the the peaty, moisture-retaining mix, the small plant can't use up all the moisture so the roots sit there in excessively wet soil that doesn't dry out — an invitation to anaerobic conditions that lead to rot.

However, if you use an extremely gritty, fast-draining soil for your xerics and Mediterraneans, you can plant in larger pots because the water will drain enough to leave oxygen around the roots. They will need watering more frequently than if planted in peaty mixes, but it will also be virtually impossible to overwater them and they'll be more likely to survive winter.

I'm not suggesting to use a monster container right away, but I have no problem putting a 4" pot into 10"-13" for the first year. My summer climate is similar to yours.

Thanks that helps. I've been using Kelloggs organic Raised Bed and Potting Mix Premium Outdoor Container Mix. It seems to drain nicely - I water every few days and the soil seems to dry out evenly throughout the pot. And I don't see any sogginess in the soil.

Okay. I was just sharing my technique and experience re pot size. That looks really heavy and I would keep to small pots if you're using it. And cut it 50-50 with pumice or perlite for the Mediterranean plants.

How do you know it's drying out evenly throughout the pot?

I have a moisture gauge and checked my pots in multiple spots when I first started with containers - close to the plant and further out in the pot. The moisture has been pretty consistent throughout the pot. If the outer edges of the pot are in the dry (red) zone, the area closest to the root ball is rarely above the bottom of the yellow zone. And that's within a couple days of being watered. I haven't had any pot be in the green at the root ball and dry further out.

I suspect that with our temps, no soil will retain moisture for long. And the bulk of the plants are in full sun so get the brunt of the drying heat.

I'll get some pumice to mix in as I repot into bigger pots.

With salvias, how big of pots do you find your plants end up in when full grown?

I figure I need to start stocking up on planters but not sure what to be looking for. And I'd like to add more salvias around the concrete patio in containers - salvias seem to be very happy here and are easy maintenance and will offer a variety of colors.

I love salvias, in part because so many like this climate. I'm rebuilding my garden after a couple of years' neglect, so my examples are limited. The largest pots I have them in at the moment are about 14x14" ish and I think they're either stunted or in decline.
Look:
These are two Clary sages (Salvia sclarea var turkestanica 'Piemont', aka Italian clary sage) and basic Salvia sclarea. Both are described as biennials or short lived perennials and are in their third years. This is new spring growth; they'll get bigger


Same plant last year


BUT here is a volunteer from last summer's seed that just popped up in the gravel path. What a massive difference in size! The yardstick is just to give you an idea of scale. Do note where it's from.


My point is that the pot size can affect the plant size. They all do better in the ground. Although here's a Black&Bloom from a few years ago; it got huge. So....ymmv

I love the yardstick!!!

Do you think bigger pots would help the ones that are stunted?

I know my salvias will grow out of their current pots (6" and 10"). And while I'd love to put them in the ground, I'm just out of ground space at this point. So, I want to give them as much chance as possible to succeed in pots.

No idea about the two clarys. Soil could probably use a refresh. If they're actually biennials, they're on borrowed time anyway.
I've had a S. greggii in a 10" pot for two years that's done quite well. Needs up potting this year. Related to your S. x jamensis.