TIMING: In general, the best time to plant trees is early spring (March through early May) or in the fall when temperatures are cooler and trees are dormant or nearly dormant. Trees can be planted in the winter if the ground is workable. It is best to avoid the hottest part of the summer (late June through August) for all trees. Timing can vary depending on the growing and planting methods used. Keep in mind that significant cutting or shearing of roots, such as with container grown stock, should not occur when the tree is most actively growing (May-July). This is one reason why fall can be a good time for the planting of such trees. Ideally the digging of trees for transplant should occur in late winter or early spring before bud break and then again in the fall and early winter after leaf drop. Most evergreens are best dug in early spring before candling (bud break), and gain in late summer to early fall when there is still some growing season remaining after digging.
SITE PREPARATION: In general, trees grow best in native, healthy top soil. Healthy soils are highly organic and are alive with a myriad of insects, fungi and microorganisms. Avoid planting in sterile fill soils and soils that drain poorly. On sites with poor soils, it is especially important that species selection be carefully considered. Compacted, sterile and degraded soils can be improved by working in organic matter (compost, mulch, etc.) and planting deeply-rooted or nitrogen-fixing grasses and perennials. Another strategy is to plant soil building cover crops a year or two before planting trees.
PREPARING THE HOLE:
- Dig a saucer shaped hole wider than the root system so that there is room for loose soil to be backfilled around the root ball (see attached diagram). The hole should not be dug deeper than the root mass. Time should be taken before digging to figure out how deep the root mass will be by locating the first main lateral roots and measuring to the bottom of the root mass (see discussion below on root depth). If the hole has been dug too deeply and needs to be raised, the bottom should be tamped firm enough to prevent the tree from settling deeper after planting. This is especially important when digging the hole with a mechanical auger – deeper is not better!
- The soil should be friable and workable at planting time, not excessively dry, hard, wet or gooey. A small spade-fork comes in handy to help break up soil clods. For excessively hard or chunky soils, a small rototiller can be used to till up the planting site before or during the planting process. Care should be taken to not destroy the surrounding soil tilth with excessive tilling.
PLANTING THE TREE:
- Planting elevation. Plant so that the base of the trunk is at the original ground level or slightly higher. The trunk flare or root collar, the transitional area between the stem and roots, should be visible above grade. In heavy, clay-dominated soils and soils that stay wet longer, the tree should be planted slightly above grade (2”-4”) with the soil sloped gradually back to original ground level.
- Root depth is critical! Regardless of planting elevation, the first lateral roots should end up just under the soil surface (1” to 2” deep) and the trunk for most species should flare visibly where it meets the ground. Always locate the first main lateral roots and remove any excess soil above them before setting the plant in the hole. The first main roots are often several inches below the top of the container or root ball. All graft unions should be visible above the soil line.
- Remove all plastic containers, fabric containers and grow bags before planting!
- Remember that the primary goal of planting is to insure a laterally spreading root system! For container-grown trees, carefully remove any loose growing medium from around the roots by shaking, soaking or washing with a hose. Exposing the root system helps reveal circling, hooking and girdling problems and will also allow for better root-soil contact when the tree is planted. Circling roots should be loosened and spread laterally if possible before planting. Cutting of larger roots that can’t be straightened may be necessary to prevent girdling and to better insure a laterally spreading root system. This includes any hooked roots that are growing downwards. Recent research is showing that the shearing of the 1-2” outer layer of tightly circling and matted roots at the container’s edge may be necessary at planting time. The shearing can be done with a sharp spade after the tree is in the hole and properly backfilled. Keep in mind that significant cutting or shearing of roots will shock actively growing tree, making the timing of such cutting important (see prior discussion on timing).
- For balled and burlap (B&B) trees in which root integrity can’t be guaranteed before planting, NFS recommends removal of the wire basket and burlap at planting time. The primary purpose for this is to help expose the root system so that any root problems can be corrected before planting. It’s our experience that much of the soil ball can be allowed to fall apart or even be carefully removed before planting without harming the integrity of the tree (see discussion on timing). The simplest method is to remove the wire basket and burlap before carefully placing the tree in the hole. If maintaining the integrity of the soil ball is important or is required by the nursery, then the tree can be placed in the hole first before the top 12-18” of the wire basket and burlap are cut away. Excess soil over the root ball should be removed at this time and the roots should be examined for any problems such as hooking or girdling. Remember to check for proper planting depth by locating the first main lateral roots before planting. A surveyor’s pin is a good tool for this purpose. Finally, cut away any twine or tying materials that may be wrapped around the base of the trunk. Many trees are girdled And die for lack of this simple effort.
- Once the tree is set in the hole, it should be backfilled with the original soil dug from the hole. Large clods and soil chunks should be broken up before backfilling. Composted organic matter or good top soil can be added to the backfill if desired, especially if planting in poor soils. The tree should be watered during backfilling to help remove air pockets and moisten the roots.