These are questions that people often ask, and it's important to understand that they're not really the questions that you need to know the answers to. The when and how much are always dependent on the moisture in the soil, the light, the rate at which the plant uses water, the type of plant, and so on. So I want to give you some tools that you can use to figure out for yourself the when and how much.
As I said earlier, you can measure the water by using any container - 1/2 a pitcher, 1/4 of a bottle, etc. - but you can also measure by learning to count! This means that as you pour water from your watering can, you count at the same speed every time, and depending on how fast or slow you count, and the speed at which the water comes out of the spout, you can tell exactly (exactly enough for your purpose, anyway) how much water you're pouring. This is extremely useful.
It's easy to remember, and allows you to generalize to plants you've never seen before; it saves pouring into a measuring device then pouring into the plant; it's easy to make adjustments - for instance, if you give a plant an "8" count, and it's too wet the next time you come to it, you know that "8" was too much for it, so you might try a "4" to allow it to use extra water from the "8" watering, and then the next time, try a "6". Trust me, it's easier than it sounds.
First reach well down into the soil with a spoon and pull up some to test its moisture and make up. If your sample doesn't come from near the bottom of the pot, use a probe also - you really need to learn the moisture level down near the bottom . Don't forget to jot down the moisture level in your notes. If the moisture level is 6 or under, go ahead and water, making sure to count and record the amount of water you put into the plant.
When you pour water into a plant, you don't want to dump it all in one spot, you want to pour all the way around the plant at the edge of the soil. If the soil is very dry and pulled away from the pot, push it snugly back against the side of the pot before you pour. Lift up the leaves if you need to, to get under them and to keep from splashing. Most of the roots are concentrated around the outside of the soil mass, close to the sides of the pot, and you want to make sure all of the roots are moistened. The objective is to water enough to get a run-off into the liner of 1/4 -1/2" if you're watering on a weekly schedule, or 1/2 - 1'" for a 2 week schedule.
Remember, consistency is a goal. Plants seem to respond well to receiving the same amount of water at regular intervals, and to a constant cycle of abundant moisture and gentle aeration. Always remember to check the soil moisture, though, because water usage can change throughout the year with changing seasons, as the plant grows, or if it's dealing with some kind of stress.
If the plant is too wet - hasn't yet reached it's recommended % of aeration - first check the liner. Use a dipstick if it's a large plant, difficult to see inside. If there's water in it, your work is done. Don't add more water, but you can leave what's in there for another week. Don't leave water in the liner for more than 2 weeks, though. If there's still water in the liner after 2 weeks, you'll need to siphon it out.
If all the water in the liner has been used, but the soil when you squeeze it has visible water coming out, again, your work is done, you don't need to water this plant. If the soil doesn't have squeezable water in it, but the moisture level is still higher than you would like - say a 6 when you'd like to have a 3 or 4 - water it 1/2 the amount you did the previous time.
A plant that is too dry - % of aeration is higher than recommended - obviously, is going to need more water than you gave it the last time. A good rule-of-thumb is to give it 1/2 again more water than you did at the previous watering
That's the end of this excerpt from The Color of Your Thumb Has Nothing To Do With It.
For those who prefer details and exactitude, and who like to have lists and tables to post in strategic positions, the book has some lovely ones showing the range of possible NML's (Numerical Moisture Levels) under differing light conditions, and the adjustment to make in watering amounts.
The book will be available for purchase at our website, along with full length video version of the text. Keep watch for the announcement of the due date. (Yes, it's something like having a child.)
Next time I'll be touching on the special watering techniques for low and high light. As always, if you have any questions, or ideas for subjects you'd like to talk about, please chime in on the comments.
See 'ya soon.
(by Marlie Graves)