1 Year Old Katsura not so good
Hi, Master Gardner(s): Last October (2017), we had a 10 gallon Katsura planted in our garden as part of a major landscape project. It leafed out nicely early this year. Now, the leaves don't look so good (though, they have not dropped en masse). We live in concordia neighborhood, and as you know, it is a hot summer. Early in July I started watering it 15-20 gallons/week via 5 gallon bucket, AND, it is on a drip irrigation. In late July, I increased the drip by 50% (plus the 15-20 gpw via bucket). The nearby paperbark maple (about 12ft away), which sees same light, shade, etc. is doing well (same drip and bucket support). Nearby plants and shrubs are all doing well. Am I over-reacting? Over watering? Underwatering? Thank you for any insight you can offer!
Multnomah County Oregon
Katsura (Cercidiphyllum japonicum) is a lovely small tree, appropriate for city lots, and it has wonderful foliage that starts purple, becomes green, and turns gorgeous yellows, oranges, and reds in fall --but it requires well-drained soil that is kept moist, but not soggy, all year.
From your photos, your Katsura's leaves are show both drought stress and sun scorch. And also from your photos, it looks like you may be aiming for a drought-tolerant yard.
As the Sunset Western Garden Book says, "Katsura trees need regular moisture (especially during youth), and shelter from intense sun and drying wind." The Sunset writers are probably cautioning gardeners in Arizona, but the important peculiarity of our Willamette valley climate is our long dry summers--this summer longer and drier than most--and Katsura is definitely NOT "climate adapted" for this part of the world. It is a beautiful tree, but will always require serious summer water.
You don't mention how much water you are providing by drip. Each emitter is labelled to provide a specific number of gallons per hour. Katsuras need moist soil, and even several scattered drip emitters will probably not keep enough of the soil area moist. Instead, try a soaker hose spiraled multiple times from slightly beyond the drip line in toward the trunk, and run it long enough to keep all the soil area moist down a foot--which probably means running it overnight, probably a couple times a week. A 3 inch layer of mulch or tree chips will help reduce evaporation and even out temperature and moisture swings, and is an excellent investment (apply it in a uniform depth from outside the drip line to within a couple inches of the trunk--again, this is the area to be kept moist). Starting in late summer, you can reduce water to increase the intensity of the fall color, but the soil should never be allowed to dry out.
From your photos, your Katsura stems look long and leggy. Did you add fertilizer at planting time or afterward? It is always better to avoid amending the soil into which trees are planted, and for most trees it is generally a good idea to avoid fertilizer later. For Katsuras, more than a very little fertilizer promotes leggy growth that more susceptible both to early and late season cold damage, as well as summer heat stress.
To recap: keep the soil damp but not soggy all summer. This is one of our most beautiful trees and ideal for smaller yards. But it is not for xeriscaped gardens!
HorticultureWeek is written primarily for English professional gardeners, but their climate is often surprisingly similar to here, and they published an interesting article on these plants: https://www.hortweek.com/cercidiphyllum/landscape/article/1210660
Thank you so much for the timely and detailed response! We’ll implement right away.