PeeJay teaches us about wet/dry cycling

PeeJay;2550853 said:

For Sue and anyone else interested I'll post some observations about watering and wet/dry cycling.

The first thing to ask is, "how dry should it get?" You don't really want the plant to suffer on the dry end. That said, if you've never let the plant get to the point where is shows obvious signs of being thirsty you can't really know what the limit is...

How do I know when the plant is showing obvious signs of being thirsty? Well, it's obvious. That sounds patronizing but it isn't that simple. As usual an analogy might be useful.

Many years ago I aquired a TRD off road Tacoma. It is a decent 4x4 but by no means a highly modified offroad beast. My son who was about 12 at the time and I were headed up to Ouray in Colorado to meet up with some extended family. When we got to Silverton I decided to head up the Alpine Loop which is a 4x4 road in the area. Once we had gotten up high I noticed a road heading down a gulch. My map indicated that it was a shortcut to Ouray. There was a modified Tacoma and a tricked out Jeep parked at the road junction. I stopped and asked the drivers if they had come up the road and if they thought it was possible for me to go down it.

The guy with the truck walked behind my truck and looked at the hitch. "You will bump that heavy duty hitch at the bad spot" he told me, "but yeah, you can make it down that."

"The bad spot? How far down is the bad spot?"

"You'll know it when you see it", he told me. "There are winch points anchored in the rocks there for people coming up. Just be careful there. You will bump your hitch but it is heavy duty and won't get damaged."

The boy and I started down the road and it got pretty awful in a hurry. I repeatedly came upon knarly spots where junior had to get out and spot my line. Each time he did I wondered if that was "the bad spot." I didn't see the winch points... The going was slow. The prospect of turning around and going back up was not fun. Then we got to the bad spot and I KNEW we were there. Before that I was merely wondering if each bad part of road was the bad spot. The guy at the top was right. When I got there I KNEW it. There was no doubt.

"What the heck is PeeJay going on about? How does this even relate to watering my pot plants?" you may be asking yourself. In order to understand the wet dry cycle you need to let the pot dry out until the plant starts to show signs of being very thirsty. You'll know it when you see it. On the way there, if you've never been down that road, you will look at the plant with skepticism and wonder if you have let it get dry enough. But, when the plant starts to show obvious signs of dehydration you will KNOW it.

That road we were on is called Poughkeepsie Gulch by the way. You can google it and watch videos of people destroying their vehicles at the bad spot if you are so inclined.

It can be nerve racking getting to the bad spot with your plants. At least you don't have to drive your truck down the wall when you get there. You just water the plant and it bounces right back.

Now then, the goal is not to get the plants THAT dry every watering cycle. What going to the edge does is help you learn the dry end limit. You get a sense of the weight of the pot when it is getting critically dry. If you don't have a sense of the limit then you will probably always water too frequently. Trust me, the plant will not suddenly die if you turn your back on it for a few hours as things start to dry out. Test the limit and learn.

The next problem is how much to water when you do water? There is no set amount. You can't really say, I will water 2 quarts. The goal is to thoroughly soak the the soil. The soil is well drained, hopefully with perlite or lava rock or whatever. You want to get it to where it's holding all the water it can hold.

Many times you'll see people say that you should water until there's runoff. That can be very deceiving. In nature the soil dries out after watering from the top down. This cycling promotes healthy balanced micobial activity and a robust root-soil interface. When the soil on top is dry it does not readily accept moisture when you water it. Think about a celluloid kitchen sponge. If you let it get bone dry then stick it under a stream of water it doesn't spring right back to it's hydrated state. At first the water will bead up and run off. It takes a little coaxing to get the sponge ready to soak up the water. The same is true of soil. That's why in dry climates or times of drought there is a huge danger of flash flooding when it rains hard. The soil isn't ready to absorb all that moisture and it runs off.

When it is time to water you need to give the plant a little and leave it for a few minutes. Then, go back and do it again. Hit the pot with water in stages until it is holding all the water it can. In larger containers this can take a bit of time.

I was talking about this with someone once and took a picture to illustrate. I poured about a quart of water on a plant that was ready for watering until I got runoff. Then I lifted the rootball out of the pot and took a picture of it.

Because I hadn't "coaxed the sponge" into accepting water, a lot of water ran across the top of the pot and found the path of least resistance - down the junction between the soil and the container and out the drain holes. Sure I had gotten runoff, but the plant was not well watered. If you look at the picture closely you can see water paths. Most of the root ball is still dry.

In summation it is very useful to understand the dry limit. Once you know where that is you can water before the plants get there but not water too soon. When it is time to water, water slowly and thoroughly. This top down drying of the soil is what happens in nature. It promotes healthy and robust soil/plant metabolism far more effectively than things like ACTs. It isn't that hard, really!

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