How do you determine how much to water native bushes and trees?


I am in charge of watering a newly established native bush and tree garden. I know that I should water if we do not receive 1 inch of rain per week. I have been trying to understand your native plant bulletins, but they are not all that easy. Many note that I should add 1 inch of water. How does one measure one inch of water for a 6 foot tall balsam, by way of example. I have been studying Cornell’s sites, etc. Ok, please help! Here are some plants I need to water if I do not get an inch of rain:
1. Spice bush (one foot tall) – was in a one gallon container
2. Northern bayberry – 2 feet tall, one gallon container
3. New Jersey tea (Ceanothus Americanus) – 1 foot tall, 1 gallon container
4. Gray birch – 3 feet tall
5. Black cheery – 2 feet tall
6. Rose viginai – 2 feet tall
7. Sweet fern – 1 foot tall
8. Cornus racemosa – 1 foot tall
Anything you could add would be so helpful!


Jonathan Foster, Home Horticulture Outreach Professional

The 1 inch per week rule is really more of a guideline, and as you recognize, one that it sometimes difficult to measure and/or implement. It often seems to be as much art as science. The Univ of MN Extension has a nice resource on watering the vegetable garden here–while you aren’t growing vegetables, there are some good suggestions like monitoring weather reports, setting out a rain gauge, and using a water meter on your hose.

All of that said, most shrubs and trees like to be well-watered for the first couple of seasons after planting, and these are all quite young. Once established, rainfall tends to cover most of your irrigation needs (barring drought conditions), but early on you should be giving them extra attention. Experienced gardeners use the finger technique, whereby you push a finger into the soil near the plant and see how the soil feels–cool and moist (not wet) means thing are good, dry/warm and crumbly means it’s time to water. This gets easier with practice, so I encourage you to test at various times–e.g., when it’s dry, after a rain storm, after you’ve watered, etc.–to get a feel for your soil under various conditions.

Also be watching for signs of water stress. Many plants droop a little during the hottest part of the day and recover when things cool down, but if you notice the plants not bouncing back it’s time to water. I should note that all of this advice assumes good drainage of the site. Waterlogged soil, frustratingly, can make plants exhibit symptoms similar to water stress, so the finger test is an important technique to double check. If the soil is moist, don’t water even if the plant looks droopy, as insufficient irrigation probably isn’t what’s going on.

I would also put in a plug here for mulching the garden, something I consider to be an essential step. In addition to its other benefits, mulch helps keep the soil moist by slowing evaporation. You may not be able to mulch the plants you still have in containers, but watch more closely in hot weather as they’ll dry faster than those in-ground.

Happy gardening.