castorp, I have grown tomatoes and herbs quite successfully in "Earthboxes" which have a reservoir in the base and an overflow opening on the side. There is 'wick' composed of the potting medium contained in a tube which dips into the reservoir. I would fill the reservoir until water came out of the overflow opening. At first the interval was maybe 3 or 4 days. As the plants matured and bore fruit, expectedly, I had to do this almost daily. Elsewhere there is the "Lechuza" planter. Apparently one has to top water the plant for a lengthy period to tempt it to send its roots through a layer of supplied medium, then through a perforated plate and into the water reservoir below. Thereafter, water is supplied into the reservoir as indicated by a floating indicator. They do recommend that the plants be 'dried down' in what I interpret to be a cyclic program. My conclusions from all this? If one is doing subsurface irrigation, the medium must permit water movement upward. Depending upon the plant this movement upward may need to be limited. The tomato plant prefers a free draining soil and it readily sends out roots from the stem near the base. I found it useful to have a pretty coarse mix in the top six inches of the "Earthbox". Moulding up of tomato plants in the ground takes advantage of this rooting habit. Finally, long ago and far away, we constructed a crude hydroponicum to grow sugar cane plants from cuttings. The cuttings were held in holes in a cardboard cover over the container of nutrient solution. The first cuttings all rotted because we had neglected to provide aeration. Thereafter we always left a space in which roots developed to provide that all important aeration. I guess that this is a good point to stop.

collect rain water and use only rain water and you will be fine. Do not use chemical fertilizers. The wrong water and chemical fertilizers cause a build up of SALT. and salt kills plants. rain water is naturally soft with no salt. chemical fertilizers are SALT. they are 100% pure salt. The plants can not use it all and the salt builds up. If you need ferts use organic fertilizer like manures etc. If the plant gets too salty then you need to drain lots of clean rain water down through the soil and dissolve the salt and then out the holes in the bottom. One advantage or disadvantage is that with holes in the bottom the roots can grow down into the soil below. this can be good or bad depending on if your soil is bad with disease and nematodes. good in the sense that if the roots grow down into good soil they find more moisture and usually the plant will grow bigger.

I have a grand total of one planting w/o a drain hole. It's a very shallow penjing arrangement. That it's shallow allows me to easily determine how wet/dry the soil is at the bottom of the 1-1'2" deep tray, which knowledge I consider mandatory. I also use only distilled water, water from the dehumidifiers, or snowmelt to irrigate with to eliminate salt build-up, which is a death sentence in containers w/o holes. Finally, I use fish emulsion fertilizers to help guard against the accumulation of unused fertilizer salts. The planting is in its 5th or 6th year and doing well, but you can see by my outline that you cannot treat a planting w/o a drain hole like traditional container plantings and expect it to be problem free. Al

I have only a tiny phone screen to view the photos, so I can't see them well enough to be of much help. When I zoom in they just become pixilated. Hopefully someone else with a larger screen will pick-up your thread, but here are a couple of things to check: On the cactus, is that crusty stuff part of the cactus, or is it definitely something stuck to it. Is it really a cactus, or is it a Euphorbia? If it bleeds white, then it is a Euphorbia. Physical damage, like heat, sunburn, frostbite, or something rubbing, bumping, or chewing it can cause scarring. In Euphorbias, it might also cause that milky sap to "scab." See if you can gently hook it with a fingernail and peel a bit off, or maybe slide a fingernail or thin credit card under it. At least then you'll know if it is a scar, scab, or something else. Some bugs will pack together and stack up on cacti - mealy bugs, I think - but I don't think many pests bother Euphorbia. That sap is nasty. On the Dieffenbachia, I can't see well enough to even be sure where the holes are. Brown tips, and brown holes or spots can occur from poor drainage, worn out soil, or being root bound. How well does it drain when you water it? Can you pull the whole plant and its soil straight out of the pot intact? You might check that. It's somewhere to start, anyway. I wish I could see it well enough to offer more help. If you upload larger photos I might get a better idea, but hopefully you'll get more input than just mine.