So far, this spring has been a bit brutal for new and even existing plants here in Michigan. Most of April and May were cloudy, cold, and wet, with some areas down to southwest lower having freezing temperatures at the start of Memorial Day Weekend. The switch to dry - and even hot weather, with a few days already of 90 degrees, has been rather abrupt.
If you happened to have planted in late May or early June, as I did, it was especially harsh for new plants that did not have access to a regular water supply. One of the biggest reasons new plantings fail is a lack of water during the "establishment period," when new plants start developing their root systems.
In my mind, I think of two establishment periods, the first 4-12 weeks after planting (if planting in the spring through early fall) and the second establishment period being the next three growing seasons.
New Perennials
Many of the plants you buy in the spring are coming from a coddled life inside a greenhouse, and like all newborns, need, or should I say, REQUIRE your attention early on.
I try and water new perennial plugs and larger plants every day for the first two weeks - and then every few days for the rest of the 12-week establishment period.
Of course, all soils are different, and if you have sandy soil, it will be tough to overwater, as the water moves quickly through the ground, but if you have clay, the area you water could stay moist for days, enabling you to water less.
A good rule of thumb (literally) is to stick your finger into the ground, and if the first few inches of soil are moist, you don't need to water.
If you plant in the late fall when rain tends to be more frequent and the air cooler, you can water every 2-3 days- but continue to do so until frost.
Since most perennials I plant are native and chosen for the appropriate site (I don't grow moisture-loving plants in a hot, dry sandy site), I don't water after the first year - establishment period.
New Trees and Shrubs
The larger the plant, the more at risk they are of dying in the first season - usually due to a lack of water. When nature propagates a new plant by seed, that seed spends time establishing a root system to prepare for its growth above ground; not growing (above ground) more than the plant's root system can provide water and nutrients.
When we plant a gallon-sized jug-root ball in the ground or even larger for balled and burlapped trees and shrubs, the roots only extend as far out as the actual root ball.
This means the tree, shrub, or large perennial is unable to access any water beyond its physical root ball until it has time to extend its roots further into the surrounding soil.
Newly planted trees need 20-25 gallons of water per week for the first two weeks and then watering every 2 -3 days for the rest of the first establishment period (12 weeks). Many people suggest (and I agree) that you should water new trees for the first three growing seasons.
So if you plant in the summer, you would water all summer, through the fall, and then again the following spring - soaking the root ball every 2-3 days.
You can estimate the amount of water needed by the caliper (diameter) of the trunk, about 1-1.5 gallons per 1-inch caliper of the tree trunk.
A 1-inch diameter tree needs about 1-1.5 gallons of water at each watering, and a 3-inch diameter tree needs about 3-4.5 gallons each time you water.
Shrubs
Depending on the shrub's size, I make sure to soak the root ball every day for the first two weeks, then every three days for the rest of the 12-week establishment period, and then 1-2 times per week for the rest of the first growing season.
I don't typically water shrubs after the first growing season unless they are very large.
The most important thing you can do to help plants get established is to keep them watered and mulched for the first year or two.
After that, I like to plant a mass of native carex and sedges around the trees. These small "grass-like" clumping plants have dense root systems extending 1'-2' into the ground that holds water, providing new trees with a steady moisture supply. And the best thing - no more mulching!
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