What Do I Fertilize My Walnut Trees With?

Determining Fertilization Need

• Understanding of the base soil nutrient levels can help correct imbalances before problems develop. Take a soil sample before trees are planted and on a regular interval, approximately every 3 to 5 years. Observe annual shoot growth, leaf color and nut production. The appearance of the leaves is considered one of the best diagnostic tools, because it will frequently provide the first indication what nutrient is necessary. In addition, look for 18 to 30 inches of annual growth in young walnut trees. A lesser degree of growth is an indication that nitrogen levels are low.

Fertilizer

• In order to obtain optimum growth, you must maintain adequate levels of nitrogen. Provide nitrogen if less than 18 inches of annual shoot growth occurs in trees 10 years and under in age. Nitrogen urea is recommended as a usable source of the nutrient. Recommended doses vary by age of tree. Apply 1/3 to 1/2 lb. of urea per tree for trees 2 to 5 years old, 1/2 to 3/4 lb. of urea per tree for trees 6 to 7 years of age and 3/4 to 1 lb. of urea per tree for trees 8 to 10 years old. A balanced 12-12-12 fertilizer may be used instead of urea if phosphorus and potassium levels are also low. Be advised that proper pH is as important as nutrient levels and availability. Make sure soil pH is between 6.5 and 7.2 at planting. Monitor soil pH levels periodically to ensure the pH stays within this range. Add lime, as needed, to maintain this level.

Fertilizer Application Timing

• Do not fertilize walnut trees during the first year after planting. The root systems of the tree, before they are well-established, are readily damaged by sudden spikes in nitrogen levels. In addition, any fertilizer treatments during this time will likely stimulate weed competition. Fertilization of pole-sized trees will provide better results and greater economic return. Add lime to improve soil pH at any time of the year. Provide nitrogen-rich fertilizer at the start of active tree growth, in March or April, to ensure that trees will make the most out of it. Apply fertilizer in five-years intervals, or as needed, based on leaf or soil analysis results.

Caution

• Injury from insects, herbicides or equipment can sometimes be mistaken for nutrient deficiencies. Before applying fertilizer, use diagnostic tools to ensure you are treating a nutrient imbalance. Only apply nutrients to correct confirmed soil deficiencies. Do not apply more fertilizer than necessary, as it can be toxic. Be aware, fertilization results are not instantaneous. The response to the fertilizer will not be apparent in nut yields until the second year following fertilization.