Guidelines for Nursery Tree Quality
These documents were published by the Urban Tree Foundation and developed by a committee of horticultural professionals from the nursery, landscape, municipal, consulting, and academic sectors.
Tree Planting Specifications
California Department of Forestry and Fire Protection
1) All tree planting stock to be planted using these "Planting Specifications" shall conform at minimum to the Specification Guidelines for Container-Grown Landscape Trees issued by the California Department of Forestry & Fire Protection (CDF); (Appendix E)
2) Trees are to be planted in accordance to the landscape plan as well as adhering to current recognized horticultural practices.
3) Trees shall be planted so that the root ball is equal to or slightly higher than the surrounding soil surface. Shallow is better than deep! Most people plant trees to deep. A hole three times the width of the root ball is often recommended but about one-and-one half the diameter is more common. Roots can become deformed by the edge of the hole in compacted or clayey soils if it is too small. The depth of the hole should be less than the height of the root ball, especially in compacted or natural wet soils. If the hole was inadvertently dug too deep, add soil and compact it with your foot. Breaking up compacted soil in a large area (out of the drip line of the tree) around the tree provides the newly emerging roots room to expand into loose soil. This will hasten root growth translating into quicker establishment.
Proper Planting Detail - If you form a berm of soil around the root ball to hold irrigation, keep it less than about 4 inches high. Water held in a taller berm simply runs through the root ball. It might be more appropriate to make the berm from mulch since the berm typically ends up on top of the root ball eventually. Placing soil over the root ball cuts off oxygen and water.
When planting on slopes set the tree so the top-most root in the ball on the uphill side is about even with the soil. The side of the root ball on the downhill side will be well above the surrounding soil. Bring in enough soil to cover the sides of the root ball with soil. Apply mulch to finish the planting job as shown in the diagram above.
4) The trunk flare (root crown) shall be evident and free of any container soil and/or planting backfill. The trunk flare (root flare, root crown) is the abrupt swelling where roots join the trunk. This point should be visible at the top of the root ball. If the trunk flare is not visible, remove soil or media from the top of the ball until it is visible.
Bare root tree or Ball & Burlap (B&B)
Container grown tree
5) The root flare shall be slightly above the surface of the surrounding soil at all times. When planting on a sloping site, the top-most root in the root ball shall be even with the grade on the uphill side of the tree. Site soil will need to be added on the downhill side to cover the sides of the root ball and to construct the soil berm to hold water. It is better to plant the tree a little high than to plant it too deep. If the tree is a little deep, tip it to one side and slide some soil under it; then tip it back the other way and slide some more soil under the root ball. Continue this until it is set at the appropriate depth. Once it is at the appropriate dept, place a small amount of soil around the root ball to stabilize it. Soil amendments should only be used as needed. The soil removed from the hole generally makes the best backfill.
6) Tree stock will be protected from excessive vibration; avoiding being thrown or bounced off mobile equipment to the ground. Trees shall not be dragged, lifted, or pulled by the trunk or foliage parts in a manner that will loosen the roots in the ball. To avoid damage when setting the tree in the hole, lift the tree with straps or rope around the root ball, not be the trunk. Special strapping mechanisms need to be constructed to carefully lift trees out of large containers.
7) Planted trees shall exhibit no circling root conditions or evidence of untreated root bound container stock. Check rooting structure of the container tree for possible root bound conditions and implement corrections if needed.
Planting trees that are too deep in the container
When planting trees that are too deep in the container, remove all soil and media that is above the top-most root in the root ball. Cut or spread out any circling roots growing up into this media on top. Position the top-most root about even with or slightly above the top of the landscape soil.
Pot bound (also called root bound) root balls from containers have large or many roots on the outer edge of the ball. It is best not to plant trees in this condition because roots could girdle the trunk as the tree grows. The tree could also become unstable later because few supporting roots grow from the outside curved portion of a root. If you must plant a tree with circling roots, these roots should be cut with a knife or pruning tool to prevent them from girdling the tree later, especially if they are near the top of the root ball. Make three or four slices in inch deep from the top of the root ball to the bottom. If in doubt about whether a root is large enough to cut, go ahead and cut it. Research shows that if there is a growth reduction from root pruning container grown trees at planting, the effect is negligible. Other work shows a reduction in shoot growth following root slicing if plants are under irrigation. Recent studies show that slicing the root ball from the top to bottom in several locations does not increase root growth after planting. It does; however, appear to enhance distribution of regenerated roots in the backfill soil profile. Instead of growing almost exclusively from the bottom of the root ball, slicing encourages root regeneration along the slices from the top to the bottom of the root ball. This could help establish the plant quicker by allowing the roots to quickly explore a larger volume of backfill soil.
8) Trees shall all be planted in an upright position avoiding appearances of leaning. Before you begin backfilling, have someone view the tree from two directions perpendicular to each other to confirm the tree is straight. Fill in with some more backfill soil to secure the tree in the upright position. Once you add large amounts of backfill, it is difficult to reposition the tree.
9) Planting tree site (hole) shall reflect proper techniques in the use of backfill soil materials to avoid evidence of large air pockets/voids within the backfill soil profile. Attempt to break up clayey soil clumps as much as possible. Do NOT step firmly on the backfill soil because this could compact it and restrict root growth, especially in clayey soil. Fill the hole around the root ball with soil. When the hole is filled with soil, the root ball should remain 2 to 3 inches above the backfill soil. Slice the shovel 20 to 30 times into the backfill to settle the soil. Add 10 to 20 gallons of water to the root ball and backfill. Fill in any holes or depressions with additional backfill soil. Do not firmly pack backfill soil in an attempt to eliminate air pockets because this could cause too much soil compaction. The water infiltrating the backfill soil will eliminate the large air pockets. The presence of small air pockets could even be of benefit because they could allow more air to reach the roots.
10) All synthetic materials from around the tree trunk and root ball shall be removed and not evident within the backfill soil mix. String, rope, synthetic burlap, plastic, strapping, and other materials that will not decompose in the soil shall be removed at planting.
11) Optional treatment: Cover the planted tree root ball area with mulch. Apply mulch material to at least a 6-foot diameter circle around the tree. Construct a berm out of mulch at the edge of the root ball only if the tree will be watered with a hose, bucket, or other high volume means. Constructing a berm in all other situations will not provide more water to the root system. Do not construct a berm from soil since this soil could end up over the root ball several months later. Water the mulch well after it is spread. Mulching: Weed and turf suppression during establishment is essential. Application of 4+ inches of mulch (after settling) is highly recommended to help discourage weeds. This area should be maintained during the establishment period at least two feet in diameter for each inch of tree trunk diameter (minimum diameter should be six feet for trees with a trunk diameter less than 3 inches). If you wish to place mulch over the root ball, apply only a thin layer over the outer half of the root ball. This keeps the trunk dry and allows rainwater, irrigation, and air to easily enter the root ball area.
12) Support trunk staking that was supplied with the container tree has been removed. Many nursery vendors provide single or double support tree stakes to minimize trunk/crown damage during transporting activities. These support stakes left on the young tree after it is planted in the ground will often inflect wounds to the trunk and lower limbs of the young tree. This transport staking in not needed when 1) proper caliper in tree stock diameter is adhered to in the tree purchase process and/or 2) proper support staking discussed under item 13 below is utilized and installed correctly.
13) Proper tree staking utilized, if necessary. If the root ball moves in the wind, emerging roots could break and the trees will establish slowly. Staking to hold a weak trunk upright should not be necessary on trees with a trunk diameter more than about 1.5 inches. If large trees require staking to prevent the trunk from bending, it probably indicates a lesser quality tree (reflecting a failure to meet minimum container nursery stock purchase specifications). Smaller trees might require staking until enough trunk strength develops. Trees could establish more quickly and develop a slightly stronger trunk and root system if they are NOT staked at the time of planting; assuming quality nursery stock is utilized. Should staking be utilized, the following staking systems will be considered as minimum standards: Double Stake Support System, ReddyStake Support System, Alternative Staking System as illustrated.
Alternative Staking Systems
Reddy Stake Support System
Double Stake Support System
Container and bare root trees often require stakes to hold them firm in the soil until roots become established. Root balls must remain firm and stable in the soil so the fragile new roots growing into the backfill soil are not broken as the root ball moves in windy weather.
Traditional staking systems are shown in Figures 1-3. All three traditional systems require removal within one year after planting. Figures 4 and 5 show two systems used successfully by urban foresters throughout the country. Both of these inexpensive alternate systems eliminate the requirement to return to the tree to remove the staking system because they simply decay in a few years. Figure 6 shows an alternative, synthetic mulching material useful along streets and highway medians. Tree shelters or plastic tubes can increase survival of very small seedlings, but may have little or no use for standard sized planting stock. Their use has been associated with retarded trunk diameter growth, damage from birds, mechanical damage from trunks rubbing in the tube, ice and snow loading damage, reduced root systems, and delayed dormancy.
Figure 1: Three short stakes (2 shown) attached to the trunk with rubber or similar stretchable material. Stakes driven in as shown above may be better secured in the soil than those shown in Figure 2.
Figure 2: Three short stakes (2 shown) driven into soil in a traditional manner attached to the trunk with stretchable material.
Use a wide strapping or rubber to secure stakes to trees.
Figure 3: Two or three (2 shown) 2 x 2 wood stakes driven through the backfill soil.
Do not use wire in garden hose to secure trees because these can injure or girdle the tree.
Figure 4: Two or three (2 shown) wood dowels driven through edge of root ball. These do not have to be removed because they simply rot in place. There is no danger of this system girdling the trunk since nothing is attached to the trunk.
Figure 5: One horizontal 2 in. x 2 in. screwed to two vertical 2 x 2s against the side of the root ball. A second set is used on the other side if needed for larger trees.
Figure 6: Synthetic mulch, in this case made from rubber, can be used as an organic mulch replacement in areas where organic mulch could blow or float away.
Minimum Maintenance Requirements
1. Provide a minimum of weekly watering during the dry season. Keep turf and ground covers at least 18 inches away from edge of root ball. Use some type of organic mulch to retain moisture.
2. Provide developmental pruning for strong and characteristic structure at three (3) years old and again at seven (7) years old as a minimum service level.
3. Provide needed pest control for the health of the tree.
4. Provide required staking to ensure stability and proper growth. Remove the nursery stake and use two stakes placed outside the root ball and tie loosely with soft, flexible tree ties to allow for some movement. Other staking systems may be used if approved by a California Department of Forestry and Fire Protection (CDF) Urban Forestry Field Specialist.
Stake trees until the tree is capable of supporting itself in windy conditions, usually for one to two seasons.
A Guide to the Water Needs of Landscape Plants
L. R. Costello and K. S. Jones
UNIVERSITY OF CALIFORNIA - COOPERATIVE EXTENSION
Recommended Watering Practices
- Irrigate trees planted during the dry season 2 to 3 times a week for the first two months and twice a week thereafter until the rainy season. It may be necessary to water more frequently during particularly hot, dry weather.
- Construct a watering berm around the planting hole and a smaller inner temporary berm immediately around the root ball to help retain water.
- Apply water to both basins immediately after planting.
- The inner berm will help keep the root ball moist until roots grow out into the fill soil and beyond. (usually 6 to 8 weeks)
- Irrigate trees planted in the late winter to early spring on a weakly basis, when rain is lacking.
- Begin watering twice a week with the approach of warm, dry weather - apply water to wet the soil to the planting hole depth. Keep the soil moist not wet. Too much water is just as bad as too little.
- During the second year, water on a weekly basis beginning in the late spring continuing through early fall. Water the soil area under the expanding leafy canopy, allowing enough time for the water to penetrate the soil to a depth of 6 to 12". If drip irrigation is used, expand the system as the tree grows.
- By the third year, monthly deep watering should suffice.
- Many trees will thrive with 2 to 3 deep waterings applied during the summer of the fourth or fifth year.
- Some trees will survive the summer with no further irrigation.
- Most trees will benefit from periodic, but infrequent deep watering, particularly during droughts.
- It may be necessary to make adjustments in watering frequency and duration depending on soil type, weather, drainage and tree species.