ORIGINALLY POSTED AND UPDATED IN PREVIOUS HOT (HOTTER) SUMMERS, BUT STILL APPLICABLE DURING THE CURRENT JULY 2013 HEATWAVE:
July 2011 in southeast Michigan has proven itself to be dry and beastly hot. Fraleighs has been receiving a number of questions about drought stress and watering, so it might be time to summarize a few things:
With recent daytime high temperatures topping out in the nineties and marginal rainfall totals, just about the entire landscape would benefit from supplemental irrigation. This is especially true for newly planted and establishing plants. Plants selected for ‘drought tolerance’ will not exhibit this trait until their root systems are fully established. How long it takes for a plant to become established depends a little on what type of plant it is and a whole lot on how large it is at the time of planting. Smaller perennials and shrubs may only need one growing season to become established in their new environment, whereas a large tree may take several years to become fully rooted-in to the point where supplemental irrigation is a luxury rather than a necessity. It is up to the conscientious gardener to provide the additional water to ‘even out’ nature’s deficits until a plant is established.
The next question we regularly are asked to address is the frequency of watering. How often? This is never a question we can answer with a glib ‘once a day’ or ‘once a week’. Too many variables exist to have a pat answer, other than to say ‘monitor your soil moisture.’ We’ve found that a trowel and a dollop of common sense are as useful for watering as is a hose. Frequently checking the soil moisture 6-8 inches below the surface is the single best way to determine how much (or little) supplemental irrigation needs to be applied. ‘Evenly moist’ is the target for most plants, especially newly establishing ones. ‘Moist’ means neither soaking wet nor bone dry but comfortably in between. ‘Evenly’ means don’t let the soil dry out completely between waterings either. The common sense part comes in the form of ‘the hotter, windier, and drier that it has been the more frequently I need to monitor the soil, and the more frequently I’ll probably need to water’. Theprobably part kicks in because not all soil types are the same in how they retain moisture — sand dries out much faster than loam, and clay can sometimes retain irrigation too well, leading to situations of over-watering for some plants. That’s where the appropriately frequent soil moisture monitoring becomes so critical to determining how much and when supplemental irrigation is needed.
How should the supplemental irrigation be applied? Again, there is no single answer, but whatever means are used should result in ‘evenly moist’ monitored to a depth of 6-8 inches. Will an automated irrigation system make this happen? Probably, but it must be adjusted to compensate for weather and soil conditions. Will a hand-held hose work? Yes, in capable hands a hose can be very precise, but time consuming. How about a compromise (heck, even the politicians are considering it these days!) — maintain an automated irrigation system and supplement with a manually activated sprinkler on the thirstier beds? We even sell special hydration bladders (TreeCOVErs &ArborRain systems) to assist in the spot-watering of establishing larger shrubs and trees. It is also worth noting that slower, lower volume irrigation is more effective than quick, high volume waterings that tend to run off rather than soak in to the soil.
Lastly, it is worth acknowledging that severe conditions (such as the recent heat) take their toll most heavily on marginal plants; otherwise established plants that are poorly suited to their environment will be the ones that perish. If that sad outcome befalls one of your plants, be sure to mention it to our staff as you select a replacement – we’ll be glad to help you find an option better suited to your site conditions.
Update: for further information from Michigan State University on the topic, visit:
Update: for even more insight into watering techniques and hydration biology: