My Heartnut Tree Leaves Are Turning Yellow From the Ground Up

Ideal Growing Conditions

• The most robust, healthiest heartnut trees develop when grown in full sun -- no less than eight hours of uninterrupted sunlight daily. A moist, fertile soil that is neutral to slightly acidic is best. Heartnut trees, as well as other closely related walnut tree species, prosper in deep topsoils. The soil depth needs to penetrate at least 30 inches before meeting bedrock, caliche or other root-impermeable layer. When not grown in optimal conditions, a heartnut tree of any age or size may become stressed or weakened, leading to leaf yellowing.

Soil Moisture

• Yellowing of tree leaves in spring or summer most likely is caused by improper soil moisture levels. The lowest leaves in any deciduous tree canopy are the first to yellow and drop away, as they receive the least sunlight, and the more vigorous branch tips are higher up. More resources are put into the upper parts of the tree. Both an overly dry soil or a soggy or flooded soil causes leaf yellowing. Dry soil limits roots' ability to sustain foliage, while wet soil suffocates roots, blocking air exchange, killing them and reducing the number of roots absorbing water and nutrients.

Other Considerations

• Yellow leaves may also occur from disease, insect infestations or a nutrient deficiency. However, symptoms are not specifically localized only first to the lowermost branches and their leaves. Examine the tree, looking for evidence of stress coming from bugs on leaf undersides or on green stems and twigs. Strange lesions or oozing gels from the tree could suggest a disease problem. Nutrient deficiencies tend to cause irregular coloration on leaves all across the tree. If any of these problems exist, they may exacerbate the soil moisture issues. Sick, weakened trees need ideal soil conditions to combat and offset any detrimental setbacks caused by disease, bugs or lack of nutrients to conduct photosynthesis.

Recommendations

• Probe the soil around the base of the heartnut tree. Tree roots extend several feet beyond the reach of the furthest branch tips in the canopy. A hot, dry summer likely causes the soil to become overly dry, and the tree naturally sheds leaves to conserve moisture. Irrigate the soil evenly but deeply. Do not allow the tree to enter the winter already stressed by drought. Place a 3- to 4-inch layer of organic mulch over the root zone to shade the soil and conserve moisture. Do not place mulch closer than 6 inches from the trunk, as a strategy to prevent fungal diseases.