Ditch the pot, and just plant stuff. I'd avoid large shrubs, or anything particularly valuable or slow growing.

You need access to the tank for two things. Replacing the tank and pumping it out. If you have to replace the tank, you have bigger things to worry about than a garden. You will also have a backhoe. Pumping it out means accessing a small opening in the tank. If you know where that is, it isn't necessarily a big deal to move a few plants and dig it out.

This summer, my DH decided the tank should be pumped for the second time since we moved here. He took pictures, since my memory of where it was was off by a couple of feet, and he ended up having to dig a wider hole than absolutely necessary. There is a boxwood hedge on the right, and a rose and arbor on the left. The area that was dug is usually a grass path, but anything movable/disposable would do.

Pots are portable and a containerized plant is not at all a bad choice for siting where a septic system makes inground planting problematic. Here, containers with plants of all types are sited on top of septic lids - those large, plastic green disks that are impossible to disguise (and of a green never seen in nature!!). They are just moved out of the way if access to the system is required.

The concern would be with the hardiness of the plant over winter/size of the container. Plants grown in containers are more vulnerable to winter cold as they are surrounded by low temps that can easily damage unprotected root systems. Larger containers and more cold tolerant plant choices will work best.

Provided hardiness is adequate, there is no reason baptisia can't live a long time in a container, if given proper care.

Oh, I sunk the pot in the ground -- it's not sitting on top.

Plants in pots in the ground can have trouble getting enough air. Gardeners plunging potted plants into soil can have trouble with them taking root, through the drainage holes.

Baptisia roots routinely run ten foot deep, it's going to root out the pot holes strongly, while not doing as well as if you had just planted it in the ground.

Oh, and I can attest from moving a baptisia minor, that if you think you want to move it, it's probably easier/faster to just buy a new one. I moved a baptisia minor and it hasn't flowered in the three years since. I do believe in it's fourth year, it will probably flower. I could have bought another and had flowers in two...but no, I thought I could move it :)

What was the point of the pot, given this? If you are that concerned, just plant annuals there.

Woody, interesting thought...but I think I'll probably pass until someone shows me thermal readings of septic tanks (lol)...having no idea if significant heat is produced.

Another vote for not potting - my experience being a large solanum which escaped its pot (and also penetrated the paving slabs beneath). The eventual removal (when it blocked the front door) was a horror of smashed pottery and mangled paving - no way whatsoever to release gigantic rootage with a thick terracotta pot in the way...and the plant was not salvageable either, after the mauling. Being a solanum though, a root piece survived and regrew, this time without the pot. Just plant (something without the massive baptisia taproot mayhaps?) and be prepared to haul a spade out now and then.

Oh... Well, I better relocate it then. I'll leave it be for now and pull it up in the spring. I'll be enlarging the beds in the back next spring/summer, the baptisia will probably love it back there, full sun and all. The problem is I need something about 3' or so tall as a transition. Maybe some type of well-behaved shrub will do. It really is a stupid place to put a septic tank. I'd put one of those big faux "rocks" over the area, but it's right next to a wide cement walkway (I mean WIDE), that's just too much. Cr@p.

How about Amsonia hubrichtii in that spot? Should be about the right size, and IME a bit more easily moved than Baptisia. Right now mine is quite lovely, though a bit floppier than usual due to a tarp landing on top of it during a roofing project

im with woody and mad G .... lol .. how deep is the tank .. and do you know where the access cover is ...

my tanks run from about 3 feet deep .. to about 18 inches .... in mild winters the higher tank does not accumulate snow .. it melts because of the ground heat ... and if i planted on it.. i would be concerned about maintained dormancy ..... ergo.. its all grass over that one ... and over the lower one... i have an annual bed with some daylily ... all plants i would sacrifice if need be ....

you need to keep the tank cover clear .. for scheduled pumping .. but otherwise ... im not sure i would worry about planting over the rest [though i find that 10 foot root depth surprising] ....

if you have a TANK failure ... i doubt your major concern ... will be a few lost plants ...

ken

I'd say the tank is about 2 foot deep per my visual estimation. I'm aware if there is a system failure I'm up the proverbial creek - let's not even think those thoughts, that's a $$$ fix. We had the system pumped when we moved in last fall, we shouldn't need another pump for 4 years - the septic guy said 5 years between pumps with two people, but I may do it sooner

Ok, well, I pulled it up - still have it in a big pot, will over-winter it in the barn and hopefully get planted in the new sunny bed next year. In its place I planted a dwarf Colorado blue spruce, I have them dotted across the front and figured another one would add to the overall continuity of the shrub border (and man do they look good against the orange house!) I will eventually need to dig up the spruce to access the septic, so I planted it in a bottomless pot to allow for better drainage; because they don't root too deeply, will be easy to dig up with minimal damage to the roots.