Jon, thank you for the recent picture. Clearly this picture shows a plant being watered too often, and I would say based on my experience, that this is the major problem that you have. I really like your idea of bringing a scale in to weigh your containers, and from that experiment you will learn a lot about how much water is in your container at all points during the wet/dry cycle.
The sticking your finger in the top of the soil and trying to figure out whether to water or not, that is how you grow tomatoes, outside, in the ground. It is not how a container grow works, especially for a weed. Your finger sticking in the top of the soil tells you ZERO about what is happening at the bottom of the container... no matter how far you stick your finger in. As it turns out, the very very bottom of your container, where the big tap roots of a weed reside, is the most important place in that container of soil, and not the top where you have been basing your watering decisions on. Those bottom roots need oxygen every wet/dry cycle, and if they don't get it, they start to shut down. The leaf damage that you are seeing is a direct result of the plant no longer being able to supply all of its nutritional needs, because its biggest pipeline, those very bottom roots, are in trouble. Weeds are not tomatoes, and they do not like being watered too much, or being given nutrients when they cant use them... these are weeds, and they thrive in a bit of adversity... it is what they do.
Along with the above described symptom, you also have a very wrinkled and downward drooping presentation of all of your leaves. Your leaves are attempting to increase their surface area with the crinkled swollen look, so that they can evaporate water faster, trying to rid themselves of the flood at their toes. A healthy plant will lift those leaves up to the light, and they will not be all crinkled looking... they will be flat. This look of the leaves is classic, and as soon as I saw your picture I knew that watering too often was the problem. I also do not at all agree with your optimistic assessment that your new growth looks green and healthy... it looks a little yellow and unhealthy to me.
So you have been advised to use the lift method. Let me describe it for you. Take a container just like what you are using for your plant, and fill it with fresh dry soil right out of the bag. Lift it, and weigh it. This is how you want your plant's container to feel like before you water the next time. Using the scale may confuse you a bit, and realize that the scale can "see" a bit more of the water than you can "see" using the lift method, so don't go completely crazy with the scale, insisting on dry weight. It is a closed container system and it will retain a bit of moisture, and also because of capillary action, even though the rest of the container is dry, in between the roots and between the roots and the container sides, never will completely dry out. When you water by weight, get down to about 5-10% of the wet weight, and you should be good. When you lift it, you will not be able to tell much of a difference between that and the dry container of soil.
With damaged roots, it is going to take a lot longer than the 2-3 days that you have been giving them, to dry out the container. I would guess that the first few times you do this correctly, it may take 4 or 5 days to dry them out. As the roots recover however, this time between waterings will steadily decrease, and there will come a day when your plants are able to suck all the water you can give them up, in 24 hours. When you find that you are needing to water that often, it will be time to up-pot to the next bigger sized container and repeat this entire process.
Lastly, lets talk about the actual watering. It is impossible to overwater by giving too much water at any one time. It is actually your goal to water slowly, giving the soil time to absorb the water like a sponge, and you should attempt each time to "fill" that soil up with as much water as you can get it to hold, where any extra water will simply flow out of the bottom drainage holes. I even come back about a half hour after watering, and I water a second time, just to make sure that I have filled any void areas in that root ball, with good fresh water.
I weighed a container of dry soil, watered it as described here, and then weighed it again. I then put an empty cup on my scale, and filled it to achieve the weight of the water that I had added to my plant's cup. I was amazed when I learned that a good soil can hold up to 2/3 of its volume in water... the water vastly outweighing the soil. This is how much water was in my cup, and how much is suspended in solution when you saturate your container:
That my friend is a lot of water for such a tiny space, indeed all of the empty space in that cup fills with water when properly done. It then becomes the task of the plant to use all that water, and your task to wait until she has done so, before you fill her up again.
This seems to be the hardest thing for new growers of weeds to do... to be patient, and wait for however long it takes to dry out the bottom roots. If you put your plant in too large of a container and properly saturate the soil, it is very easy to drown a plant, because it could take a week or more to use all the water held in the bottom of the container, and by that time the top of the plant's root system will die because it has been dry for the better part of a week. Big containers kill weeds... so that is why we recommend solo cups at the beginning and always using the smallest container possible as you build up the root ball.
You can recover this plant, but it is going to take patience. If you are in there puttering around and changing something every day, you are probably not doing this right. There are many times that I water my plants and then walk away from my tents for 3 days, knowing that everything is fine. Trust your plants... they know what to do. When you are waiting for them to drain the water, trust your plants again, and know that they will tell you when they want water. A healthy plant will definitely will tell you when it needs water. You want to water just before the point that the plant will start wilting due to a lack of water, and please take this as the truth... it is better to let her wilt for a few hours needing water, than to do as you have been doing, keeping her wet. For about a day, a strong healthy plant that is about to need watering, will do something that you can look for... the very lowest leaves will start to droop. Watch for this sign, and know that she is going to need water soon... but be tough with her... she is a weed. She can handle it. Actually, when she gets to this stage and knows she is about to need water... that is when she does the most growing of new roots, seeking out new water sources. Get her to this point every time... stronger roots mean a stronger and bigger plant above.
Hope this helps... you are learning fast! I wish someone had explained all this to me when I was new, you are lucky you found 420mag! Good luck, you will be on the way to recovery soon!
