I’m used to the pines in my garden looking a certain way. They usually yellow a little in fall and green up again in spring – only this spring, many remained yellow.
I figured part of that was a result of fertilizing late this year. But even after fertilizing for a couple of months, many of my pines remained yellow. Here’s an example of a yellow pine next to a greener one.
Young pines with yellow and green foliage
Among a group of these young pines, about one third were green and the rest were yellow. Looking closer, it turns out the yellow pines were in a different soil mix.
The tree on the left is planted in a mix of 75% pumice and 25% mulch. The tree on the right is in a mix of 30% akadama and 70% pumice and lava.
Over the years I’ve grown healthy pines in both of these mixes, but I’ve found that their water needs are different. The pumice and akadama mix dries out quickly, and the pumice and mulch mix dries slowly. When I keep trees in the two mixes together, I end up overwatering the mulch mix which contributes to the yellow foliage.
A second factor working against the mix with mulch is that the organic material I used is likely spent after a year and no longer offers much nutrition. When I grow pines in pure pumice mixes, I find it can be difficult to keep the trees green, possibly due to pumice’s low cation-exchange capacity (CEC – a soil particle’s ability to hold onto charged particles like fertilizer).
If the mulch has completely broken down, the pumice has trouble holding onto fertilizer, and the pines stay yellow.
Problem solved? Not quite. The pines below are both planted in mixes with pumice and akadama.
Yellow and green pines
For the last fifteen years, I’ve grown pines on the same few benches in my garden. This spring, I moved a few of the pines in colanders to a spot on the ground toward the back of the garden. The trees on the ground were dark green.
I can think of a few differences between these two environments. The trees on the ground stay cooler when it’s warm and warmer when it’s cold. It’s a bit less windy and possibly more humid near the ground. There’s also more available water as the excess sits on the ground before soaking in, and the spot on the ground gets a bit less sun than the trees on the bench.
Every one of these differences favors the production of green foliage on the trees growing on the ground. I don’t know how much greening is attributable to each, but as soon as I noticed this I moved a lot more pines onto the ground.
Now we’re getting close to solving the puzzle – but not quite. A small number of pines on the ground were still yellow. They were in good soil, they were fertilized regularly, and there were no signs of pests – not even root aphids.
That’s when I started thinking about how hard is was to get my trees to green up this year. And that’s when the light bulb went off.
Before I even checked, I knew what the problem was. It hadn’t been a problem for a couple of years, but apparently it was bad this year (it was). It was the pH of the water.
I got out the pH meter and was disappointed by the reading: 9.1
A high pH reading
As a sanity check, I looked up the pH reported by my water utility: 9.35.
And that explains the yellowing. I’m happy – and a bit amazed – that so many of my trees were getting by with such basic water, and even happier that I now know what to do to green up the last yellow trees in the garden: acidify the water. More on that topic in the next post.
Subscribe to Bonsai Tonight
New Posts Delivered Every Tuesday and Friday