How often to water Japanese maple in California

In July, established Japanese maple in loam needs a deep watering about every 8 days in the Central Valley, about every 11 days on the south coast and about every 5 days in the South Inland zone. Sandy soil holds less water, so waterings come closer together. Clay stretches them. Check the soil before each watering and skip one after a soaking rain.

In July in the Central Valley, established Japanese maple needs about 6.8 gallons a day under a 10 foot canopy and about 27 gallons a day under a 20 foot canopy. Give it in deep waterings spread days apart rather than a little every day, so the whole root zone gets wet.

Yes. WUCOLS rates Japanese maple separately for each of the six California climate zones: moderate water in the North-Central Coastal zone, moderate water in the Central Valley zone, moderate water in the South Coastal zone, high water in the South Inland zone, not suited to this region in the High and Intermediate Desert zone, not suited to this region in the Low Desert zone. The monthly table above shows how the same rating translates into different gallon amounts as reference evapotranspiration changes.

That is leaf scorch, the most common complaint with this tree in California. Dry soil causes it, but so do hot wind, afternoon sun and salty irrigation water, so a scorched tree is not always a thirsty one. Check the soil first: if it is moist a few inches down, the fix is afternoon shade, mulch and an occasional extra-long soak to flush salts, not more frequent watering.

Yes. This tree wants moist soil, not wet soil, and roots sitting in waterlogged ground rot quickly. Yellowing leaves across the canopy, leaves dropping early and a tree that wilts even though the soil is damp all point to too much water or poor drainage. Let the surface dry slightly between waterings and fix the drainage before adding any more water.

Keep the root ball evenly moist through the first summer, checking it whenever the surface starts to dry, because a young maple's small root system dries out much faster than the soil around it. Shape a shallow basin of soil around the planting hole so water sinks in over the roots instead of running off, and mulch the whole area. From the second or third year the roots reach wider and the tree can shift to deep, less frequent soakings.

Drip works well as long as it wets a wide area rather than one spot at the trunk. The roots are shallow and spread to the edge of the canopy and beyond, so place several emitters in a ring near the drip line and move them outward as the tree grows. Run the system slowly and long enough to soak deep, and give an extra-long run once in a while to carry salts below the root zone.

In the ground, usually not. The tree is leafless and dormant, and California winter rain covers its small cool-season need in most years. Water only during long dry stretches between storms, and keep an eye on container trees, which still dry out in winter, especially under eaves where rain never reaches.

Summer leaf drop is usually the tree shedding scorched leaves after a heat wave or a stretch of dry soil. It looks alarming, but a maple that drops crispy leaves in July often pushes a fresh flush of growth once steady moisture returns. Resume deep, regular watering and hold off on fertilizer; if the leaves drop while still green and the soil is soggy, suspect root damage from overwatering instead.