Extreme weather can hurt your trees and shrubs

Garden's Grace shrubs and trees

We all become tree-huggers in the spring…. Bright green, nascent green shoots push out into a fresh, clean world and begin their journey of showing off and growing through the season. Lurking in the wings, like a Normanesque stalker of Hitchcock fame, are the slings and arrows of summer weather–rain, humidity, heat, diseases and wind.

As we pass the mark of midsummer and Fourth of July, some of these characters come into the light of day and spoil our idyllic view of our gardens. Some of the results are treatable, some can be remedied through cultural practices while others are like the pesky neighbor or relative that we just learn to live with.

Here is a quick run-down of some of the most common spoilers in the summer landscape and what can be done to minimize their impact.


A chlorotic sweetgum leaf showing the green veins and yellowed foliage that are typical.

A chlorotic sweetgum leaf showing the green veins and yellowed foliage that are typical.

Especially in years of frequent rain, nutrition becomes a factor to  shrub and tree health. The big three nutrients–nitrogen, phosphorus and potassium–are the building blocks that help woody plants build carbohydrate reserves and flood the atmosphere with oxygen. Of those three, nitrogen is the first to go, because it is quite soluble in water and will move readily in the soil profile, sometimes leaching beyond the reach of  shrub and tree fibrous roots.

“Chlorosis” is the name we give this condition that is easily identified by dark green leaf veins surrounded by yellowish leaf tissue. Fertilization with nitrogen as a key ingredient is the solution to this problem. Slow release pelleted fertilizers like Osmocote are good solutions to this fertilizer need, as well as foliar sprays like Miracle Gro that will put the nitrogen-based nutrient right where it is needed. Some trees, especially birches and pin oaks, are frequent exhibitors of chlorosis, mainly because clay-based soils tend to hold on to their nitrate compounds due to higher alkalinity in the soil. In this situation, a product like aluminum sulfate or similar acidifying agent can improve soil pH and make nitrogen more available. Chelated iron is a more available iron complex known to green up chlorotic leaves.


Heart rot fungus.previewWoody plant diseases come in several different guises, but usually environmental conditions or insects are the agents that spread these summer garden spoilers. Especially years where high humidity and cool nights are common, fungal diseases flourish. We often see these in the form of mushrooms growing on wood or spots and masses growing on the leaves. In the case of shelf mushrooms on tree bark, these are quite serious because they often attack the strong heartwood of the tree. Careful removal of the mushroom can help prevent the threadlike mycelia that are akin to roots from infiltrating the important layers of tissues that shuttle water and nutrients up and down the trunk of the tree.

On the other hand, leaf-borne diseases like powdery mildew and leaf spot are often a blemish to the good looks of the plant but won’t affect the long-term growth of the tree or shrub. Some types of plant diseases can be treated with sprays, but most common cultural practices like removal of infected leaves, thoroughly cleaning up leaves in the fall, and thinning of branches and placement in well ventilated areas can help tremendously. There are also horticultural sprays that can reduce the impact of some diseases.

Wind damage

storm damaged tree garden's graceWith summer comes thunderstorms–beautiful and powerful. Particularly in a season like we’ve had this year, very wet soils combined with downbursts of wind can damage shrub and trees that have dense leafing patterns and catch a lot of wind on blustery days. Large trees can be toppled by such conditions, and some shrubs may put on a lot of very tender, long growth that breaks or is damaged by high winds.

Thinning of trees by trained horticulturists and arborists and timely trimming of shrubs (see our June 2015 Garden’s Grace newsletter for tips) are practical remedies for reducing the wind load on woody plants. Proper planting and maintenance can also factor into shrub and tree health during difficult periods.

We here in Iowa know that there is a price to pay for ideal Iowa weather–sunburn, mosquitoes and heat. And in the same way, we know our landscapes will endure some extremes as they thrive in summer. A healthy combination of good information, common sense and cultural control can help reduce the impact of these plants as we move on through our season.

If you’d like some help with identifying and fixing some of the issues that may be going on in your landscape, give Garden’s Grace a call today, 515-559-3049.