Bonsai Growing Tips: Clippings from August 2025

When you’re reading this, it’s probably mid-August. In Southern California it’s hot and dry most days, and you may have noticed some of your trees slowing down from their spring and early summer growth spurts. This slowdown is sometimes called “summer dormancy.” I like to call it the Summer Doldrums — a period of low activity for both me and my trees. While this summer has been much more mild than the last one, here are some things to keep in mind.

Heat can be deadly, especially for potted trees, whose roots experience much higher temperatures than their terrestrial counterparts. Keep an eye on how hot your pots are getting; you may want to move them to shade or wrap them with wet towels on the hottest days. Stone or concrete stands and benches can get especially hot — if it’s uncomfortable to place your hand on, its probably not good for your trees.

Be sure to check trees daily for water. My shohin bonsai are in shade, at least during the heat of the afternoon, and I may still need to water them a second time on especially hot days (in inorganic soil).

Oil based pesticides (e.g. neem oil) can smother plants in the heat, preventing the transpiration that our trees need to keep themselves cool. I’m not big on oil in general, but I absolutely never use it during hot weather. If I need to spray for pests this time of year, I prefer soapy water, sprayed in the evening and rinsed off after 15 minutes or so. I’ve been seeing a lot of clients struggle with juniper scale this month, so keep an eye out!

Defoliating Deciduous Trees: By this time of year, many of my deciduous trees are looking a little rough. Between the heat and the low humidity, maples in particular are often a bit crispy. Defoliating now can yield a fresh crop of leaves in our “second spring” (a period of renewed growth after a summer break) but be careful to protect new shoots from late summer and early fall heat waves. You may need to do the famous “bonsai shuffle,” moving trees in and out of shade depending on the weather. Only defoliate trees that are healthy and strong enough to push another flush of growth before fall, and remember that if you wait too long, the tree may just start its winter nap early and you won’t see foliage again until spring.

Removing Wire: Make sure to check any trees that were wired earlier in the year. Fast early summer growth can really sneak up on you, and this slow period is a great time to remove wire, preventing scars.

Taking It Easy: I like to give my temperate trees a bit of a break this time of year. I avoid heavy wiring/bending and trim refined trees minimally. Warm weather is a great time to make jin though, so if you are planning large branch removals on raw material, the live cambium is much easier to strip now than it will be in the fall, when there is less water in the tissue.

Tropicals: These plants like the warm weather, but remember that most of them are from HUMID warm environments, not the near-desert of So Cal. Keeping them out of drying wind, and in some partial shade will help keep them going strong. I will be winding down tropical repotting this month, so that any freshly repotted trees can get well established before they start to slow down as the days get shorter and the nights get cooler in the coming fall. Most of the ficus I defoliated last month are roaring back with vigorous growth, so I’ll be trimming shoots back to the first pair of leaves long as they continue extending.

We are very fortunate to have such a long growing season in Southern California, but it sometimes helps me to think of it as two shorter growing seasons per year — one in spring, and another “second spring” round of growth after the Summer Doldrums. It doesn’t seem like there is much to do aside from watering right now, but a flurry of activity will be coming soon. See you next month!