The terra cotta walls and bottom are gas permeable, which means they allow water vapor to pass through the walls. This dries the soil faster and helps air return, which helps to reduce the negative impact of to heavy soil that doesn't want to drain. It also allows foil, growth inhibiting gasses like methane, CO2, and sulfurous compounds that build up under anoxic/anaerobic conditions (soggy soil) to escape through the container walls. Please don't take what I say as argumentative. I WANT you to do well, so I'm still going to encourage you to try to understand the principle of perched water in containers and how it is affected by soil particle size. Even if you only use the info to help you deal with heavy soils, it's better to have knowledge on your side. It only LOOKS daunting. Most people get the concept right away. It took me a long time before I could say this because it sounds like I'm boasting, but I'm really not: Literally hundreds of people, both newcomers to container gardening and those that have been gardening for a very long time, have said in so many words that "Now I finally get it. Now I understand why I was having so much trouble growing in the soils I was using ....." and so on. One way or another, you'll have to deal with the fallout when using heavy (water retentive) soils. I, or others here, can help you avoid the issues by helping you build a soil that better suits your application, or by offering tips that can at least partially reduce the negatives you're dealing with. Drainage layers or gimmicks aren't going help, but tilting your containers after you water and using a wick can help considerably - it's in the link I offered. Good luck. Al

sandl...if you don't want to drill a hole in it, then maybe you can put a piece of ceramic tile (or something similar)over the top to keep the water out. You can always set a plant on top of that for more decoration, if you want. but I'm sure you can successfully drill a hole in it with the right bit. there was a discussion on here last year maybe about this very thing. The poster had a good suggestion , but I can't for the life of me remember what it was. Something about using a masonry bit and putting a piece of wood down first, then drilling through the wood to get to the pot? I don't know if that makes sense, but do a search on here and see if that post pops up.

From afar, with nothing to go on but your verbal description, and since there is only SPECULATION about the cause of overflowing -- not confirmed facts -- the advice is no more than speculation about the prognosis. A "dip," though it wouldn't be a great thing in a drain line, may or may not make a difference in flow. (Degrees matter.) If the drain overflowed but was not clogged, it seems that it didn't measure up to the capacity needed. This is a common problem. 4" lines are used even when 6" and 8" lines should be installed. A french drain being installed along the foundation MAY help, but the term "french drain" means different things to different people, so the details will matter. For all practical purposes, during a hard rain, it's not going to matter if there is foliage or roots "to absorb water." It will come down to grading and drainage. Rocks around a drain won't necessarily matter either, unless they wash & clog the drain. If debris is clogging the drain opening, a good thing to do would be to install a drain cage. Chances are, though, that your real problem is capacity.

@annecoria - Here is a static view showing an edge of our patio. The retaining wall surrounds the entire patio with block approximately 12” below grade. The block rests upon 6-8” of comoacted stone which functions as a French Drain. The drain empties into the low grade between houses. Even following very heavy rainfall water emptys within an hour. You can shape a French Drain as needed to direct water away Our patio is crowned at 1/4” per foot both away from the house and outward from the center. Hope this helps.