Spring is my favorite time of year in the garden. It’s also a rather challenging season when it comes to watering.
Without checking the soil, it can be hard to tell how much water a tree needs at a glance. Take, for example, the two young junipers below.
Cutting-grown kishu shimpaku
For the past week, I’ve been watering the tree on the left twice a day and the tree on the right once every two days.
This might seem natural as the tree on the left has more foliage than the tree on the right, but that doesn’t account for the dramatically different water needs.
Here are two more junipers that are closer in size but with the same variance in water needs.
Needs water twice per day; needs water once every two days
The main difference is that the trees on the right were repotted this year and have yet to establish new roots. The trees on the left have been in their pots for one year. Even though all four trees are the same age, the ones with more roots are drying out much faster than the recently repotted ones.
I’ve found similar patterns among my pines. The tree on the left was repotted this year and needs water every other day. The tree on the right was repotted a year ago and needs water every day.
Twenty-four and fourteen-year-old black pines
The main takeaway for all of the above trees is that repotting can have an effect on a tree’s ability to take up water.
Is this pattern the same for all of trees in the garden?
Nope.
The juniper below was repotted one year ago but only needs water once or twice a week.
Kishu shimpaku grafted on California juniper
The tree is recovering from some stress a couple of years back. Last summer I watered it once every one-to-two weeks. It’s drying out faster this year which I take to be a good sign.
My deciduous trees and broadleaf evergreens follow no patterns at all.
Potentilla – repotted this year, needs water daily
Cherry plum – repotted this year, needs water daily
Korean hornbeam – repotted this year, needs water once or twice a week
Dwarf wisteria – repotted last year, needs water once every four-to-five days
Olive – repotted last year, needs water no more than once per week
While the watering rates above are accurate, they have little bearing on what the trees will need next week. The stage of growth for each tree – and the weather – will determine whether or not I’ll need to water them on any given day.
Despite this apparent complexity, the basic test for whether or not a tree needs water remains simple. I check 1/4″ to 1/2″ below the surface of the soil with my finger and only water when the soil is beginning to dry out. If it’s wet, I gently sprinkle the foliage but try not to let much water hit the soil. That makes for a lot of checking this time of year, but the effort can go a long way toward ensuring the trees enter the warmest time of the year in good health.
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Dane buxbaum says
I have a dwarf crape myrtle that I wintered this year in a greenhouse that never dipped below 60 degrees. It’s leaves turned red orange around January and eventually dropped. I then trimmed some of the dead ends down and when I saw no growth response for over a month. Another month passed and I got concerned thinking it might be root bound. It was close but not there yet. I did a very light trim of the roots just to give them some soil to grow into and have heat watering to a minimum. Still no growth at all. Fortunately a little scrape on all the major branches reveals green and all the crapes outdoors in the ground have been very slow to bud only this past week showing signs of life. We had about a week in January when it never got above freezing. That cold snap was not preceded by any appreciable precipitation so everything outdoors is kind of behind schedule. Every year I struggle with whether to put my small temperate trees outdoors under mulch or house them in the greenhouse. Any ideas about winter weathering indoors vs outdoors for deciduous trees and junipers?
Jonas Dupuich says
Great question Dane and likely a very good one for the forum (https://ask.bonsaitonight.com/) as I don’t have a lot of experience with this.
A month below freezing sounds hard! I’d want to keep temperate trees indoors for such a cold spell as bonsai can really dry out during extended periods of cold. The typical approaches to indoor storage are keeping the tree just above freezing or just below it (in the 28-32 range).
Edward Stanton says
Jonas, thanks for the nuanced treatment of watering in today’s blog, enhanced as always by superb photographs. As I was reading it, a rainstorm came out of nowhere and soaked my trees, making me realize that your article today is written by someone who lives in an arid region where you can control your trees’ moisture much better than I can. In a rainier region like mine (Kentucky), nature makes some of the decisions that you must make yourself in Alameda. There are advantages in both cases, but I admit to preferring a less perfect control of my trees’ moisture but more watering by rain.
Jonas Dupuich says
Thanks for the note Ed – I also prefer it when it rains! It’s only problematic when there’s too much. In these cases I’ll either place a block under one side of the tree or move the tree under an eve or some similar place where it gets less rain. This is generally more of a problem later in the growing season – and not in dry climates like mine!
Jonathan says
Great post! I have a costal Redwood that I just repotted this year. What’s your experience in watering habits for this species at this time of year? I live in Los Angeles.
Thanks!
Jonas Dupuich says
Thanks Jonathan – great question! I find redwoods interesting. The main thing that determines water requirements for redwoods is often their stage of development. I have a redwood that when potbound needed watering once per day, even in winter. After strong cutback the tree still dried out but not as frequently. And since repotting it a month ago, it hasn’t dried out once! I overhead water every day and haven’t needed to water more than once or twice a week. The lesson so far is to not expect the tree to grow much when pruned during the dormant season.
Blake says
Very interesting sir. I’m in the UK and not unlike Ed, the watering regime is dictated to by the weather here! Been raining, reasonably heavily almost everyday or at least 4 times a week for the last month! My pine are really suffering, the akadama is more or less black . No where to hide them we just use a very free draining mix and then pay the price in the summer.
Jonas Dupuich says
Wow – that’s a lot of rain! I’ve seen photos of some gardens with covered structures just to keep excessive rain away. The block trick can help keep the trees from becoming waterlogged. Good luck with the rain!