Dear Doug,

Thank you for contacting Ask Extension about your Kousa dogwood. We will need more information to try to assist you.

• When was the tree planted?
• When did it start to decline, and what were the symptoms?
• Why do you think it may be over-watered?
• What fertilizer(s) if any have you applied, and how often?
• What kind of soil do you have (sand, clay) and approximately how deep is it before you hit hardpan?

I can see from your photos that the roots are exposed. This usually indicates they have not been able to penetrate deep enough into the soil. Without the additional information, I can suggest you apply up to 1 inch of finished compost across the entire drip zone (not just the bare ring), and keep 3 to 4 inches of landscape woodchips over the area to protect the roots as well as the soil. 

Please respond directly to this email and I will be happy to try to advise you further.

Thank you for your assistance. I’ve addressed your questions below. Perhaps you will be able to follow up with some additional observations based on my responses. In any event, I will add compost and wood chips soon as you have suggested. I suspect that it is too late this year to see a marked improvement from these steps, but will be watching for better growth next year.

Good morning, Doug. Thank you for writing back. I do not see your answers. Was there supposed to be an attachment? Perhaps you can copy them directly into an email response and resend them. 

Thank you for your continued attention to this. I'm sorry that the inline method I used to answer your questions did not work. So, here goes:

The dogwood was probably planted in 2009, or within a year or so of that.

I’m not sure how well it was doing last year, but I didn’t really notice the markedly smaller leaf size and overall coverage in the canopy until this summer.

I'm wondering about over-watering or drainage issues because there is a puddle of water around the tree after the sprinklers have run. It does dissipate fairly soon thereafter. I have cut back slightly on the application of water, but am concerned that that more would result in sacrificing the lawn. I don’t think I can do much about the drainage as the lawn is on the high side of the house.

The tree has only received fertilizer in conjunction with a fairly light annual application of fertilizer to the lawn. However, I did just put some fertilizer stakes around the perimeter of the tree. I also have put down compost and mulch since I first contacted you.

We tilled in compost and top soil several years ago when we planted the lawn. That probably only extends 6-8 inches, then there is a layer of clay. I would have dug a 3-4 foot wide hole and mixed in gardening material when I planted the tree.

Dear Doug,

Thank you for sending additional information. Kousa dogwoods typically have leaf blades that range in size from 2 to 4 inches. Generally, smaller leaf development on trees is a result of nutrient deficiencies, heat stress, or water stress (too much or too little.)

It is possible that a combination of factors may be impacting your dogwood. Certainly, the extreme heat episodes of this year and the last may have stressed the tree. Kousa Dogwood is not particularly drought- or heat-tolerant. 

While they require irrigation during periods of heat or drought, Kousas prefer well-draining soil with mulch or leaf litter over the roots. 

Clay soil does not drain well and the puddling is a sign that water is draining poorly. Excessively wet soil can cause root rot and may deplete the soil nutrients through leaching. On the other hand, shallow soil can quickly dry out, further stressing the tree.

As you describe it, there is a hardpan of clay beneath 6-8 inches of heavily amended soil. The exposed roots in your photo are an indication that the roots cannot penetrate the clay hardpan, which likely adds to the heat stress. Tree roots usually grow 12-18 inches deep. However, now that the tree is established, it would be detrimental to change the level of soil within the drip zone.  

For this reason, I suggest adding about an inch of finished compost once or twice a year to the surface of the soil (ie. not worked in.) Avoid tilling or disturbing the existing soil as this can damage the small feeder roots responsible for taking up nutrients. The organic matter will slowly decompose and perk down through the soil, improving both the tilth and the drainage over time. Maintain 3 inches of organic mulch (such as landscapers' woodchips) at all times. It is not necessary to remove the mulch when applying compost. 
 
For future reference, the current best practices in sylviculture recommend against amending soil when planting a tree. In fact, some experts recommend washing off all of the nursery soil (ie. root washing) so that only the bare root and native soil are placed into the planting hole. This encourages strong roots and avoids the tendency for the roots to begin circling in the planting hole causing them to girdle the trunk.

This may sound harsh, but you may have to choose between what's best for your lawn vs. a healthy tree. Lawn irrigation may not provide sufficient water for your dogwood. A tree of this size and age needs at least 20 gallons of water each week (rain and/or irrigation.) Irrigate when the soil feels dry 2 inches below the surface (excluding mulch) or when there is less than 1 inch of rainfall per week. Use a rain gauge or tuna can to measure precipitation.

Typically, a good soil profile consists of about 50% space. This space contains fluctuating amounts of air and water. Too much or too little water can kill small feeder roots. Apply water very slowly so it does not puddle or run off. Drip systems are best, but some fountain-type sprinklers will work as well. 

This article provides more information:
https://www.google.com/url?client=internal-element-cse&cx=<personal data hidden><personal data hidden>:r0tg5erstn8&q=https://www.oregon.gov/odf/Documents/forestbenefits/watering-fact-sheet.pdf&sa=U&ved=2ahUKEwiKpdnOodeAAxWsFlkFHWFJCJsQFnoECAcQAQ&usg=AOvVaw3-6VO4EojKxzh5vv9Xk4Jo

I hope this information is helpful to you and your tree. Please write again whenever you have questions.

Thank you very much for this information. I will keep it in mind going forward and will employ your suggestions regarding compost and mulch. Also, I'll double-check my irritation schedule.