Adapted from the article “Guidelines for handling and planting bareroot walnut nursery trees” by Carolyn DeBuse, Former UCCE Farm Advisor, Solano and Yolo Counties and Bill Krueger, UCCE Farm Advisor Emeritus, Glenn County in the October 2012 Sacramento Valley Walnut News.
Walnut bareroot trees look sturdy but they are very vulnerable to environmental stresses of heat, freezing, and drying out. Their outward appearance may be unchanged, damage can decrease their survival or increase possibility of disease. Here are some guidelines that will help ensure their health.
- Prepare the orchard site before delivery of the trees. Professional tree cold storage is the best place to store trees once they are dug from the nursery field.
- Once trees are picked up or delivered, keep the roots moist and protect the trees from sunlight, heat and extreme cold. Do not pick up more trees than you can plant in a day. Plan to plant the trees as quickly as possible after delivery.
- If trees have been in cold storage, continue the cold storage at your orchard while planting by renting a refrigeration truck trailer. Trees must be kept moist even in refrigeration.
- If refrigeration is not possible, store the trees in a cool fully enclosed warehouse keeping the trees moist and covering them with a tarp.
- Continue keeping the trees moist and cool while moving them to the field and during planting. Take the trees from your onsite storage or refrigeration in very small lots. Move them under tarps or covered trailer, keeping them in the shade as much as possible. Keep them moist by spraying them with water while waiting to be planted. If possible move the refrigeration truck to the field and remove trees as needed.
The most important detail is to manage soil settling so that after a few months of settling the trees are at the same depth as they were grown in the nursery. A tree planted too deep is more susceptible to Phytophthora crown rot from moist soil against the upper rootstock portion while a tree planted too high can get sunburned roots and dry out too quickly. The following guidelines will help to avoid problems while planting your trees.
- Field soil should be moist but not overly wet for planting.
- Dig the holes just deep enough for the roots. A deeper hole will settle the whole tree lower than desired.
- Augered holes should have the sides roughed up with a shovel to disrupt glazing and prevent roots from circling rather than growing out into the soil.
- Planting on berms or mounds is recommended to allow proper drainage from around the crown of the tree and reduce the chance of disease.
- Trim off broken roots or roots that are too long for the hole. It is best to enlarge the hole to fit the roots than trim them but this is not always possible.
- K-84 bacteria can be used before planting to protect the roots from crown gall. The success of this spray will depend on the type of crown gall bacteria found in the field. It works with some crown gall strains and not others. If used, it is better to spray it on the roots and crown rather than dip trees.
- Use a planting board to ensure that the crown of the tree is in the proper position and slightly above the soil level. This will allow for some settling so the final tree placement is at the proper depth.
- Spread the roots in all directions in the hole. The strongest roots should be placed towards prevailing wind.
- Fill the soil around the roots and pack it down multiple times in the process of filling. Make sure there are no voids under the root system. The soil should be mounded above soil level to allow for settling.
- Water the tree in with 1-2 gallons of water to help remove air pockets and help settle the soil.
- Head back the trees at 4-5 good buds above the graft or bud union. This will ensure that only a few shoots will start to grow maximizing growth from stored reserves in the tree and decreasing shoot competition.
- Paint the whole tree with a white wash to prevent sun burning. This is critical and should be done the same day as planting. Be sure to paint the crown of the tree all the way down to the soil line. (whitewash: latex interior paint cut with 50% water)
- First irrigation should be applied after the trees have begun to grow.
Additional planting notes
- Do not place fertilizer or organic matter in the hole.
- Avoid planting on extremely hot days. Trees dry out too quickly between storage and planting and can be heat damaged if they are not painted and watered in immediately.
- Placing stakes at planting can save the extra step of post pounding and they are ready to go when the trees need staking. For standard spaced orchards, use 10 ft. stakes and place 2 feet below soil level and 8 feet above. Eight foot stakes (2 feet below and 6 feet above) work for hedgerow orchards. Stakes should be placed 12 inches away from the tree on the side perpendicular to prevailing winds with the tree tied loosely to allow for movement and strong trunk development.