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Plant Answer Line Question

Keywords: Magnolia, Climatic zones

Will the evergreen magnolia, Michelia wilsonii, grow in Danville, CA?


It is suitable for your area in Danville (according to the Sunset Western Garden Book). As far as surviving the full sun in your hottest summers, you might want to check with a local nursery about that to be quite sure. The Sunset book says it needs partial shade in the hottest climates [that it grows in], and your Sunset zone appears to be 9, which suggests it has high summer temperatures. It may need to be planted where it will get partial shade.

Date 2019-11-07
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Plant Answer Line Question

Keywords: Plant litter, Plant physiology, Magnolia

I have noticed that Magnolia leaves seem to decompose more slowly than other leaves...can you tell me why that might be the case?


There is a lot of anecdotal evidence regarding your observation. Finding information to specifically confirm it is not easy, however. But some facts about plants physiology help, especially in combination with considerations about the conditions required for decay. I referred to Introduction to Plant Physiology (William G. Hopkins, 1995) for most of the information below.

Lignin is a compound that is an integral part of the cell walls of plants. (It is the second most abundant organic compound on earth after cellulose.) Lignin fills the spaces in the cell walls of various plant tissues, providing mechanical strength to the cell wall and thus to the entire plant.

Lots of lignin in a leaf would result in a slow process of decomposition because it is difficult to degrade. That is, it is not easy for bacteria and water (necessary for decomposition) to penetrate the chemical structure of lignin.

Suberin is a waxy substance that is highly hydrophobic (repels water); its main function is to prevent water from penetrating plant tissue. Suberin is found in the outermost layer of the bark (in the dead corky tissue). The cells in this layer are dead and abundant in suberin, preventing water loss from the tissues below. Suberin can also be found in various other plant structures, including leaves, where it also prevents the movement of water.

So, the combination of a structural function of lignin and the water-repelling characteristics of suberin - in leaves, in this case - is quite helpful in explaining why magnolia leaves decay at a slower rate than other leaves.

An article about composting from University of Florida Extension mentions that magnolia leaves would need to be shredded in order to be usable in compost (or as mulch).

Date 2019-05-10
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Plant Answer Line Question

Keywords: Pruning trees, Magnolia

I have a Magnolia tree that is planted next to our house. This year, there were not very many blooms and the tree is getting rather bushy-looking. When is the best time to prune it and how much can be pruned?


According to the American Horticultural Society's book, Pruning and Training by Christopher Brickell (DK Publishing, 1996), mature Magnolias should not be pruned unless it is essential. Many species will bleed from pruning wounds, and should only be pruned from summer to before midwinter. Summer-blooming Magnolias can be carefully pruned to reduce size by removing selected branches. The book Pruning: A Practical Guide by Peter McHoy (Abbeville Press, 1993) recommends doing this in late fall or early winter.
Below is a link to an interesting discussion on the how and why of pruning a Magnolia, from University of British Columbia Botanical Garden's online forum.

Date 2019-06-08
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Plant Answer Line Question

Keywords: Magnolia, Container gardening

I recently purchased a magnolia that had no tags on it. I have an extremely large pot that I would like to plant the magnolia in. My books at home lead me to believe that I should plant it in Azalea and Camellia potting mix. A local nursery has advised me that this would be fine, although another has said no. They also disagreed with my plan of putting rocks, bitumen, and old leaves in the bottom of the pot to help with drainage. They believe a quality potting mix and nothing else is the way to go. What are your suggestions?


Here is what the book, Magnolias: A Gardener's Guide, by Jim Gardiner (Timber Press, 2000) says about growing Magnolias in containers:

...considerable experience is needed to retain magnolias in a container for any length of time. The roots are particularly sensitive to being hot and dry during the summer months and frosted during the winter months... Evergreen magnolias and clones of Magnolia grandiflora, in particular M. grandiflora 'Gallissonniere,' can be grown in very large containers for indoor use in atria.

I think if you take the matter of extreme heat and cold into consideration, you should be able to grow your magnolia in a container. I would be curious to know which species you have, because some get very large, and for these a container might not be a good choice. Magnolias prefer good, free-draining acidic soil that does not dry out, according to Rosemary Bennett's book, Magnolias (Firefly Books, 2002). Since Azaleas also prefer acidic soil, the idea of using Azalea and Camellia potting mix makes sense.

You may find the following information on growing trees in containers helpful:

Virginia Cooperative Extension: Trees for Landscape Containers and Planters

University of Tennessee Extension: Trees to Plant in Containers or Wells

UBC Botanical Garden Forum: A discussion on requirements for magnolias in containers

UBC Botanical Garden Forum: A discussion on potting guidelines for a particular magnolia This discussion suggests that the container should be filled with soil-based compost which provides some nutrients to the plant.

As for container drainage, here is what Prof. Linda Chalker-Scott of Washington State University says. In short, she says that putting coarse material in the base of a pot for better drainage is a myth.

Date 2020-01-23
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Plant Answer Line Question

Keywords: Woody plant propagation, Magnolia

I have a Magnolia wilsonii in my garden, and this year there is a definite profusion of seed that followed a long flowering season (I'm collecting more every day). What is the best way to sow and grow these?


According to the American Horticultural Society's Plant Propagation, edited by Alan Toogood (DK Publishing, 1999) you can collect fresh seeds in the fall, and thoroughly clean them (the book recommends using a fungicide to prevent rot or damping off). To extract the seeds, gather the ripe cones and dry them until the fleshy fruits come away. Soak them in warm water with liquid detergent for a couple of days to remove the outer coating. Once softened, drain the water. Remove any flesh still attached, and dry the seeds with tissue. Sow fresh and overwinter in a cold frame, or mix with moist vermiculite, sand, or peat, and store in a plastic bag in the refrigerator for 2 months before sowing. Seedlings may be transplanted the following summer, and put back in the cold frame for a second winter.

Another method is to stratify the seeds for 3-6 months at 41 degrees Fahrenheit, sow under cover in spring with bottom heat (68 degrees) for germination to take place in about a month. It will take plants grown from seed from 3 to 10 years to flower, but some species take much longer.

Texas A & M University's horticulture department has an article on starting Magnolia from seed. The article focuses on Southern magnolia, but should still be relevant. Here is an excerpt:
"The seeds should be collected as soon as possible after the fruit is mature which is usually mid-September or early October. The cone-like fruit should be spread out to dry for several days until they open. The seeds can then be shaken from the dried cone or fruit.
"If the seed is to be kept for any length of time, the red pulp should be allowed to dry enough to lose its fleshy character, placed in sealed containers and stored at 32 to 41 degrees F. If stored over winter at room temperature seed will lose its viability. The seed should be cleaned before planting or stratifying. To remove the fleshy seed coat, soak the seed overnight in warm water. Remove the seed coat by rubbing against hardware cloth or window screening. After cleaning, the seeds should be sown immediately or stored for 3 to 6 months at about 40 degrees F and planted in the spring. An excellent way to stratify seeds is to use a polyethylene bag and place alternating layers of a moist medium such as a sand and peat mixture and seeds in the bag. Tie the top of the bag and place in a refrigerator at about 40 degrees. The medium should be just moist enough to stick together but not so wet that it will drip if squeezed by hand.
"Whether sown in the fall or stratified in the refrigerator and sown in the spring, the seeds should be covered with about l/4" of soil and mulched to prevent drying. Seedbeds should be kept moist until germination is complete. Partial shade should be provided the first summer for seedlings."

Date 2019-05-10
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Plant Answer Line Question

Keywords: Cut flowers, Magnolia

Is there anyway to slow the browning of a fresh cut Magnolia flower? I am using it as a decoration and would like to cut it the day before.


According to The World of Magnolias by Dorothy Johnson Callaway (Timber Press,1994), if you cut the flowers at an early stage (before they open) and keep them in a cool room, they will last for several days. They are naturally fragile, and it is for this reason that they are not usually used on a large scale by florists.

If you only need to keep the blossoms fresh for a day or two, then keeping them cool should be sufficient.

Date 2019-10-03
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Plant Answer Line Question

Keywords: Trees in cities, Tree planting, Magnolia

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.

Date 2019-12-18
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Plant Answer Line Question

Keywords: Tree roots, Magnolia

Does a magnolia tree root system cause cracking on the house foundation if planted too close, especially on clay soil?


What kind of magnolia are you growing? Is it deciduous or evergreen? Is it large species or one of the smaller varieties?

According to SelecTree, a website of the Urban Forest Ecosystems Institute, most Magnolias have a low root damage potential. A few, such as Magnolia delavayi, are rated as moderate. I am not an arborist, so I cannot conclusively tell you that a Magnolia will not be problematic for the house foundation. However, it is always a good idea to plant trees far enough away from structures so that you do not have to do a lot of pruning to keep them from conflicting with windows, entryways, the roofline, etc. From what I have read, most tree roots that harm foundations are not themselves causing the cracks, but are exploiting preexisting weak points in the foundation. Roots do expand in size as the tree matures, and they do seek out water to some extent, depending on the type of tree.

Below are some links to information that may be useful to you.
North Dakota University Extension
"How close to the home should trees be planted?
Large trees such as ash, hackberries, maples, lindens and oaks should be kept at least 20' from the foundation. Medium sized trees such as buckeyes, honeylocust and little leaf linden - 15-20 feet away and small trees such as flowering crabs, mountain ash and Canada red cherry - 10 feet from the foundation.
Do tree roots actually crack the foundation?
No, the wetting and drying of the clay soil causes the initial cracks. After these have developed, tree roots will grow into the cracks for moisture."

A personal essay on tree roots and foundations, from Renegade Gardener,a garden blogger

International Association of Home Inspectors
"Tree Roots and Foundations
Contrary to popular belief, InterNACHI has found that tree roots cannot normally pierce through a building's foundation. They can, however, damage a foundation in the following ways:

  • Roots can sometimes penetrate a building's foundation through pre-existing cracks.
  • Large root systems that extend beneath a house can cause foundation uplift.
  • Roots can leech water from the soil beneath foundations, causing the structures to settle and sink unevenly."

Date 2019-10-31
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Plant Answer Line Question

Keywords: Magnolia, Edible flowers

Are Magnolia flowers edible?


Buds, flowers, and leaves in various stages of growth have edible uses. According to the Plants for a Future database, "The flowers [of Magnolia grandiflora] are pickled in some parts of England and are considered to have an exquisite flavor. They are also said to be used as a spice and a condiment." Cornucopia II by Stephen Facciola (Kampong Publications, 1998) confirms this and also says that the flowerbuds of Magnolia denudata are used in Asian cuisine. After removing the calyxes, the buds are pickled and used to flavor rice, and to scent tea. In Japan, the young leaves and flower buds of Magnolia hypoleuca are broiled and eaten as a vegetable. Older leaves are made into a powder and used as seasoning; dried, whole leaves are placed on a charcoal brazier and filled with miso, leeks, daikon, and shiitake, and broiled. There is a type of miso which is seasoned with Magnolia, hoba miso.

Date 2019-12-27
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