Plant Palette

Plant Palette

TLC for Landscapes this Fall

Photo of Jennifer Schultz Nelson

Jennifer Schultz Nelson
Extension Educator, Horticulture
jaschult@illinois.edu

If I were a betting person, I probably could have won a lot wagering that we wouldn't have a frost by October 21st. Surely it will get cold sooner or later. In the meantime we have a little longer to get our gardens and yards ready for winter.

Trees and shrubs in the landscape have had a very stressful year, in several ways. We expect trees and shrubs to look their best all the time. But just like us, they may not look their best when they've been under stress.

Temperature has certainly been a source of stress this year. Starting with the ice storm last December, temperatures fluctuated wildly. As spring buds opened, the extended freeze around Easter zapped them all. Many trees and shrubs had to dig deep into their energy reserves to produce a new flush of leaves for the growing season. Soon after that temperatures soared, further stressing already suffering plants.

On top of the effects of extreme temperature swings, water was in short supply this Summer and continues to be as we move into Fall. Without adequate water before winter sets in, many water-stressed plants will not survive the winter months.

A friend commented to me recently that the trees knew it was Fall despite the warm temperatures, pointing to a tree that had leaves clearly turning yellow and dropping to the ground beneath it. Closer inspection revealed leaves edged in crispy brown, a sign that they had suffered from leaf scorch due to high temperatures and water stress prior to turning yellow.

Physiologically, the tree was trying to save itself. It wasn't getting adequate water, so it was shedding the leaves it could no longer support. A normally functioning leaf actually is part of the natural process of transpiration, where water is drawn up through the tree from the roots, then evaporates from the leaves through openings called stomata. A functional leaf in a severe drought will actually cause the plant to lose even more water, so one way to try and preserve itself is to shed leaves.

Remember though that the leaves are a valuable structure–they trap the sun's energy and the plant stores that energy to be available in the future, such as next spring. They store more than the minimum, which is why many plants that had their leaves killed in the Spring freeze this year were able to re-grow.

Potentially, a tree that has leaves lost or damaged by scorch very early in the growing season will not store up enough energy to survive the winter. One way to assess whether your leafless tree or shrub has any life left in it is to scratch the bark gently with your fingernail or a knife. If the inner layer just under the bark, called the cambium, is green, there is a chance the plant will survive. Water it well, cross your fingers, and wait for spring.

Wilting is another sign of water stress, but so is sparse or undersized foliage, as well as over-production of seeds. Excessive seeds can be another way of a plant trying to save itself. Faced with the possibility of death, the plant pours its remaining energy into future generations and more seeds than usual are produced.

Some people mistakenly think what water-stressed plants need is fertilizer. This is a huge mistake. Without available water, fertilizer will likely burn delicate roots. Even with water, fertilizer applied this time of year will encourage growth that will be much too tender to survive when cold winter winds begin to grow.

Even if you don't see many signs of water stress in your trees and shrubs, it is a good idea to give them a good drink before winter sets in. Mandatory water restrictions have recently made this even harder to do in Decatur. Watering thoroughly, about an inch per week, is much more effective than short bursts of watering.

Short bursts of watering saturate the soil very shallowly, never reaching very many roots. On new plantings this is particularly damaging, as new roots stay shallow where the water is. Thorough watering will encourage roots to grow deeper, ultimately producing a stronger plant that is equipped to access moisture deep in the soil, and tolerate drought conditions to a greater extent than a plant with only shallow roots.

In order to make your allotted watering time more effective for trees and shrubs, consider using some form of drip irrigation rather than overhead sprinklers. Overhead sprinklers tend to allow more water to evaporate before it actually reaches the ground where it's needed.

Drip irrigation, such as through soaker hoses, delivers the water directly to the root zone of plants, without as much evaporation. Place the hoses at the drip line of trees and shrubs, which is at the furthest reaching tips of the branches extending horizontally from the trunk or base of the plant. This is where most of the roots that absorb water efficiently are located.

There are commercial bags available that zip-on around the trunk of a tree or shrub and when filled with water, it slowly drips from the bags into the ground. These are great for new plantings that don't have a drip line very far from the trunk of the tree. But these bags are very expensive, often more than $20 each.

Another much more economical option is a five-gallon bucket with a few holes drilled in the bottom. Multiple buckets depending on the size of the plant, placed strategically around the drip line and filled with water will slowly seep out and soak the ground around the plant.

Turf competes with trees and shrubs for water, so even if you water your lawn, you may still need to water your trees specifically. My personal opinion is that a lawn is easier to replace than a tree or many shrubs. If I had to prioritize, I would water trees first, followed by shrubs, then perennials, and the lawn comes in dead last.

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