ASSESSING WaterING Needs in Newly Planted Landscapes
By Mike McNamara, Hoffman & McNamara Nursery & Landscape
June 20, 2025
Today's landscapes are often a complex array of various plant types with differing water needs. Further, these needs vary dramatically with changing weather patterns, soil types, elevation, sun exposure (or lack thereof), time of the year, and so on.
What follows is not scientific data, but my personal observations from over 30 years of watering experience in both the landscape and nursery setting. Yes, 30 years; Like many young people introduced to our industry, plant watering was one of my first responsibilities.
When assessing current water needs on a site, if possible, it is great to have a physical plan or map of the area that you can take notes on. If not available, simply take notes into your phone or on paper. First, observe the site very broadly. Take note of what time of day it is. When was the last significant rain event? We place a rain gauge on nearly every one of our maintained projects after we finish planting, and sometimes multiple rain gauges on the same site. We also love to use technology to help us understand the weather patterns a local area may have experienced, but it is amazing how much rainfall can vary mile to mile, so nothing beats a simple rain gauge. What is the current temperature and what have the recent temperatures been? Is it windy? Is there any water that could be hitting the site from adjacent irrigation, parking lot or roof run off? How do the plants look on a high-level? Are there variations in the turf grass color, height, health? Do the plants look lush and full or thin and stressed?
Next, dig deeper. Our trucks are outfitted with simple soil recovery probes. These are available at many horticultural outlets and take a core sample of soil to a depth that you determine by how far you insert the tool before pulling it out of the soil being sampled. If you do not have a probe, in a pinch you can even use a long screwdriver to pierce a hole large enough to feel the soil with your fingers. The point is that you want to be able to quickly move about the site gauging current moisture conditions. Pay particular attention to stressed plants, full sun areas, low ground, and areas near heat generating objects such as building structures, cars, pavement, etc.
Take the soil sample and run it between your fingers. Does the soil feel warm to the touch and crumble in your hand? Or is it cool and damp and clumps into a ball up as you roll it in your fingers? Record your findings. I find that simply putting a plus symbol (needs water) or a minus symbol (too wet) on the plan or map is efficient.
We could debate the individual needs of plants all day long and likely not get complete consensus, but I will share with you some simple generalizations I have found. A mature tree's moisture needs and tolerance are often different from those of the same species when young. For example, most mature basswood does very well in low wet ground. However, when I did my college internship at a large wholesale nursery, I learned how water-sensitive immature basswood can be. They simply do not have the root mass available to take up large amounts of water and thus need to dry out between waterings until well established when they can handle longer wet periods.
The type of planting media has a significant impact on water needs as well. For example, container grown plants tend to dry out more quickly than B&B plants. Perhaps the single largest factor affecting water needs is how long the plant has been planted on the site and thus how long it has had time to root into the surrounding soil. Sod is a great example of this. Sod often requires daily watering in the first week or weeks after being laid. However, contrary to popular practice, after the initial couple weeks of establishment, sod does not need daily watering.
While easiest to understand when thinking of an irrigation system, the concept of duration and frequency is the same whether plants are irrigated or unirrigated (only receiving natural rains). Duration refers to the amount time a sprinkler system is set to run, correlating to the amount of water applied (or the amount of rainfall received). Frequency refers to the length of time between applications (or between rainstorms). Plants have varying preferences on both duration and frequency, and we do not have time to cover all of those here but try to be aware of what the preferences are of the various plants on your site and try to appease all to the extent you are able.
For example, B&B trees planted in freshly laid and irrigated sod will require micromanagement of the irrigation. Water sod just enough to soak into the root zone and then allow enough time between waterings to dry out, encouraging roots to reach deeper, creating resilience to future weather fluctuations. Quickly adapting the watering plan and decreasing frequency as the sod becomes more rooted may save trees and shrubs from death by overwatering.
Ironically, signs of overwatering can often appear very similar to underwatering, including wilting, yellow or dropping leaves. In fact, it has been my experience that a common problem on sites is where an overwatered plant is misdiagnosed as underwatered and thus given even more water, thus compounding the underlying issue. Overwatering, among other things, prevents the development of roots and specifically fine hair roots. This leaves the plant less able to absorb water & nutrients and adapt to changing conditions. Overwatering also can lead to fungal problems like root rot and bacterial infections, in addition to high water bills.
