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?
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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