How do I go about planting a new Magnolia tree this fall?
The City of Seattle’s Department of Transportation has perhaps the best set of instructions and tips for planting trees in the Pacific Northwest. It includes a diagram of how to plant a tree. This same site also has guidelines for care of young trees.
If your tree is a “street tree” (planted in a parking strip), then be sure it is appropriate. The left-hand menu here gives lists of trees that are and are not appropriate, under Street Trees.
The current consensus is that you do not need to amend the hole with new or superior soil from another source when you fill in the hole, as this just creates an environment the roots do not want to leave. In order for a tree to become established, the roots need to grow outward, into the native soil. Washington State University Extension professor Linda Chalker-Scott discusses this subject as well as whether or not to disturb the root ball, how to handle balled and burlapped trees(remove the wire basket!), and whether staking is necessary.
The University of British Columbia Botanical Garden Forums includes the following comments about planting some varieties of magnolias:
“I would only use a well seasoned compost for a Magnolia as a top dress at planting time. We advised people to dig the hole three times the width of the root ball and place the dug out soil back in the hole with no other soil additives. Providing a root shock preventer such as liquid Vitamin B1 at a rate of one fluid ounce per gallon of water is optional. A good choice to use when planting these Magnolias on a warm day in a warm climate but generally not needed in the Pacific Northwest. What we have to guard against is planting this and others of this series too low in the ground. We like to plant these in a raised mound for a yard planting. Never plant these trees with the graft union at soil level, try to plant them about six inches to a foot above the soil level and allow
for settling in later. A Spring planting is regarded as being best for these Magnolias but in the warmer climates can be planted almost year round as our soils here seldom ever
are frozen.”
I would add to this that planting too deeply is a common mistake, but another mistake is to plant “too high” (as is suggested above, when the writer mentions planting in a “raised mound”). Some people think that such a mound can be buried in mulch; it is much better to plant at the proper depth and use mulch from about 6 inches away from the trunk to the outer edge of the root ball, creating a ‘dam’ as described by Seattle Department of Transportation.Then you can turn the hose on low and let the water fill the ‘moat’ created by the dam. During the winter, be careful that your mulch is not too deep, as it can actually keep water from getting into the soil (3-4 inches of mulch is plenty). Mulch in the spring through fall is much more important for keeping water from evaporating from the soil surface, as well as for slowing down the weeds. Be careful not to pile mulch against the trunk of the tree, as this can cause rot.
One more thing, as mentioned below on University of British Columbia Botanical Gardens Forum, do not fill the planting hole with water, as this may contribute to root rot.