I dont know if this is an issue in the UK, but here in Western Australia - what you are describing is generally caused by water repellent soil. Dusty sandy soil can prevent water from penetrating roots and deprive the plant of nutrients and water - even if you are flooding your plant. put a few drops of water into the soil. if it beads up then that is your problem. The solution is simple. buy a wetting agent and add a small amount every few months or so - via a watering can or spraying it. wetting agent is nothing more than a detergent which breaks down the surface tension of the water. You can use household dishwashing liquid but I dont recommend it for regular use as unlike commercially prepared wetting agent - dishwashing detergent will change the PH of your soil. Adding considerable organic content into your soil is also a good solution.

Perhaps a related experience: I purchased as number of sets of beautiful serving bowls with as drip glazed finish from Big Lots because they were reasonably priced and I figured I would make dish gardens with dwarf conifers purchased from Iseli's Nursery in Oregon and sell them at an art fair. Actually, our bonsai club would pick up the tab and the profits after I supplied the soil and the labor to do the potting. We bought about $300 worth of plants and maybe $200 in serving bowls to serve as pots. I drilled holes in the pots & did the potting about 2 months prior to the fair, but all the plants potted in the serving bowls were declining by the time the fair came around. I noticed that the pot finish had crazed (myriad small cracks) and some white slimy material was leaching from whatever the pots were made of. It killed all the plants, even though I unpotted them and put them in the ground in hope they would recover. Big Lots wouldn't refund my money because I had drilled holes in the pots, until I threatened to start writing letters to every town/city newspaper with a Big Lots Store & reveal what happened. I gotta believe if whatever the material was phytotoxic, it can't be good for human's. Serving bowls! You're better off using ballast in the bottom of your pots than drainage layers or charcoal. Ideally, you would be using/making a soil that allows you to water correctly (so you're flushing the soil with each watering) w/o need to worry about root health/function due to the soil remaining soggy for an extended period. Ballast reduces the amount of soil that CAN be saturated with water, and allows air to return to the entire soil volume much faster than if you didn't use ballast. It's not the best answer, but it's better than suffering the entire brunt of limitations that come with soggy soils. See pics: Al

You have to know what you're doing with rescues. And the success rate is lower than with healthy plants bought new. In addition, there is sometimes a good reason why the plant was thrown out (pest infestation, fungus, mold, other contagious diseases, etc.). Not everyone wants to hunt though things thrown out, take those risks, and wait years for a lovely mature plant (assuming that even happens). As Caro123 says, sometimes you just want a nice plant. If I were getting a first plant, I'd want to know it was healthy so as to give myself and the plant the best chance at a happy relationship. Also, when you're new to a field, it's hard to know what a good price for something is. And that is a beautiful, big, healthy-looking plant. I don't think we should be too hard on No Thanks, just help them along as requested. No Thanks, it's good that you came here. This site has lots of friendly, knowledgeable and experienced plant lovers that are happy to help. Welcome, and good luck with your beautiful plant.

I would think that if you put a LOT of weight over a shallow root system it may affect it. So try to stack them not too high - a few layers. Just a gut feeling, I have no proof of that. The other thing is oxygen - if you completely cover the soil around a plant doesn't that keep air out of the shallow soil? Although trees grow right next to pavement and in small holes in the sidewalks in cities so what do I know.