I usually check the soil with a finger - 1/2 inch deepness, if it is wet I never water the plant.

I use tap water after 24 hours keeping it in an opened bottle. In this location (Arizona) there are a lot of salts in tap water.

Unfortunately, I don't have a water softener.

I really don't know if the pot has a drain hole (I just take care of the plant temporally) - it's really difficult to check - the plant is approximately my height. But definitely no cache pot for collecting effluent is available.

I usually check the soil with a finger - 1/2 inch deepness, if it is wet I never water the plant.

I use tap water after 24 hours keeping it in an opened bottle. In this location (Arizona) there are a lot of salts in tap water. What moisture levels are in the top inches of the pot are not a reliable indicator of what moisture levels are deep in the pot. The lower 6" of a 10" pot can be 100% saturated when the top couple of inches are bone dry. The best method of telling if a larger planting needs water is by using a "tell". See something I wrote at the end of this reply.

There are good reasons not to let your water sit or rest before you use it to water. 1) It doesn't do any good insofar as allowing monochloramine or fluoride to gas off. 2) Water that's cool (even cold) and fresh from the tap holds much more dissolved oxygen, a notable plus for root health.

Unfortunately, I don't have a water softener. Perhaps that's unfortunate for people, but fortunate for plants. The Na (sodium) in the salt used in the exchange for carbonates normally leads to lethal Na levels in the soil solution.

I really don't know if the pot has a drain hole (I just take care of the plant temporally) - it's really difficult to check - the plant is approximately my height. But definitely no cache pot for collecting effluent is available. Large plantings without drain holes are decidedly difficult to grow in, so it would be best for whomever owns the plant to make sure it has one. No drain = absolute certainty all salts from tapwater and fertilizer solutions accumulate and remain in the soil. The normal outcome is loss of viability of whatever happens to be growing in the pot.

It doesn't matter if the planting has a cache pot or a collection saucer to collect the water, there should be no pathway by which the effluent that collects below the pot can make its way back into the soil. The purpose of watering to beyond the point of soil saturation is to flush salts out of the soil. Providing a pathway by which those salts can reenter the soil solution defeats the purpose of trying to flush salts from the soul before they accumulate to unhealthy/toxic levels.

..... not sure I can help much more because of the unknowns.

Using a 'tell'

Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support good root health, which is a prerequisite to a healthy plant. Watering in small sips leads to a build-up of dissolved solids (salts) in the soil, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor.

In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.

Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.

One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.

Al

Thank you so much for your absolutely amazing consulting help. I have found a wooden stick and read in the Internet how it is important to use it for big plants. Can I ask other question? It looks like I have over-moisten the plant. On new leaves I can see strange dots. I really afraid that it could be some bacteria or viruses or trouble with the roots. Could you please have a look at pictures: what to do with it, what is the possible reason?

Can I ask other question? Of course. I enjoy growing things and get a lot of personal satisfaction from my interaction with plants. Most of what I know is an outgrowth of my desire to become more proficient at bonsai, and sharing what I've learned along the way seems like a natural extension of my own growing experience. Helping others get more from their growing experience is actually fun. It looks like I have over-moisten the plant. On new leaves I can see strange dots. I really afraid that it could be some bacteria or viruses or trouble with the roots. Fungal infections are far more common than than bacterial and viral combined, and many fungal infections are very localized and consist of a small population of fungal inoculum taking advantage of a temporary condition involving a small area of the plant. Example: Over-watering often causes the plants internal water pressure to increase to the point cells rupture and leak their contents into spaces between cells. The result is a blister or wet spot on the plant that is quickly colonized by airborne fungal spores. Once the plant walls off the wound and the wound dries up, the infection is stopped from spreading. A bruise or other mechanical injury can lead to a similar progression. Other fungal infections, the ones that move systemically within the plant, are a more serious issue. Could you please have a look at pictures: what to do with it, what is the possible reason? In all honesty, it can't be said with any degree of certainty what the underlying cause was, but it's a very good bet it's related directly to root health, and that's not at all surprising because a very large % of the issues that bring growers here seeking resolution are related to root health/function. Learning how to keep a root system healthy usually always centers on the ratio of air:water in the root zone. There are several strategies that can help you limit the amount of excess water any given medium can hold, but by far, the best way is to build it into the medium before the planting is established, something accomplished by carefully assembling your media around the fact that for any given soil ingredient, large particles hold less water than the same volume of small particles. We can fix or cure excess water retention in a variety of ways that employ some very simple science, but the higher aeration of media that naturally drain to the point where levels of excess water (water that resides in what would preferably be air pockets between soil particles) becomes a non-issue makes growing sooo much easier. That reality has changed the plane on which thousands of growers here and elsewhere interact with their plants.

BTW - Plants are incapable of healing in the same way animals heal. Unlike animals, plants cannot replace or repair cells in the same spatial positions they formerly occupied. Plants are generating organisms where animals are regenerative. This means that injuries large or small will always be a part of the organism, at least until such time as the affected part is shed or removed mechanically. However, identifying the cultural condition acting as the causal stressor and eliminating it or improving it can stop further lesions from occurring and/or getting worse.

Al

Thank you so-so much! I feel the same - it could be some root issues. Just now I removed the plant from walls in order the leaves can be not in touch with hot surfaces. And I am going to proceed following the plant behavior and state. Just now I use a wooden stick to check soil moisture in all plants' pots and try to read all recommendations concerning the rules of plants' care. Just now I don't think that is a Canna rust - no bright yellow/orange circles around dots. The opposite site of a leaf looks the same. But I am ready to use fumigant in case of rust growth.