Sweetbay magnolia, also known as swamp magnolia, is a beautiful flowering tree (or shrub) native to North America that can be either evergreen or deciduous, depending on the climate where it is grown. Unusually fond of wet soil, sweetbay magnolia tends to be a deciduous shrub in the northern part of the hardiness range, a small evergreen tree in the south. Its emerald lance-shaped leaves are silver or white on the underside, and it boasts creamy white, lemon-scented flowers that appear at the end of spring or in early summer. Each flower will open in the morning and close at night, lasting for around two or three days before falling from the tree.
Sweetbay magnolia grows at a moderate rate, usually adding 1 to 2 feet per year to its overall height. They're best planted in the early spring. It's possible your immature tree won't bloom for several years, but once it does the tree will bear red, cone-like fruit in the fall once their blooms disappear, eventually going dormant in the winter (in most areas).
|Common Name||Sweetbay (sweet bay) magnolia, swamp magnolia|
|Botanical Name||Magnolia virginiana|
|Mature Size||10–35 ft. tall, 10–35 ft. wide|
|Sun Exposure||Full, partial|
|Soil Type||Moist, rich|
|Soil pH||Acidic (5.5 to 6.5)|
|Bloom Time||Late spring, early summer|
|Hardiness Zones||4–10 (USDA)|
|Native Area||North America (eastern U.S.)|
Sweetbay Magnolia Care
The sweetbay magnolia tree is a relatively easy tree to grow in full sun or partial shade location, provided you can give it consistently moist, somewhat acidic soil. In more northern climates, expect it to remain more shrubby in size and shape; it will be a decent small specimen tree in the South.
This is not a plant-it-and-forget it species—sweetbay magnolias will require annual feeding, occasional pruning, and attention to pests when they attack. But the magnificent spring blossoms make this a fine landscape specimen, especially for damp areas where few other trees thrive.
The sweetbay magnolia tree isn't too picky about the light it receives, thriving in both full sunlight and partial shade. Like many flowering trees, the more sunlight it gets (at least six to eight hours daily), the more likely it will be to be flush with blooms.
For best results, plant sweetbay magnolia in soil that is moist, rich, and flush with organic matter. Unlike most other magnolia trees, it does best in wet, boggy soils and will tolerate soils that are predominantly clay. It prefers an acidic soil with a pH between 5.5 and 6.5. If you notice the leaves turning yellow, it's a good indication that the pH levels in the soil are too alkaline and should be amended.
The sweetbay magnolia tree appreciates water and should be watered deeply as it gets established and matures. Once the tree matures, plan to water the tree as necessary, making sure the soil doesn't dry out for long periods of time. In times of warmer weather (above 75 to 80 degrees Fahrenheit), it may need additional watering.
Temperature and Humidity
Overall, the sweetbay magnolia tree doesn't have any special temperature or humidity requirements, so long as it's grown in the proper hardiness zones. These trees usually grow smaller in cooler climates, with a more shrubby size and shape.
Before fertilizing a sweetbay magnolia, perform a soil test. You should only fertilize if you have a soil deficiency. Unprescribed fertilizing (i.e., fertilizing just because you think you should) can cause fertilizer burn on these trees. It's best to use organic slow-release fertilizer, like mulch.
Types of Sweetbay Magnolia
There are several dozen cultivars of sweetbay magnolia, including some that are hybrids. These are some favorites:
- 'Emerald Tower' grows to about 20 feet, with glossy green foliage. It has been known to survive into zone 4.
- ‘Henry Hicks’ is an unusually large cultivar, sometimes growing as much as 40 feet tall. It has more columnar growth habit and is known to be evergreen into zone 5.
- 'Keltyk' has smaller leaves, a more compact habit, and is evergreen through its range. It grows to 25 feet but is easily kept smaller for use as a patio container tree.
- 'Santa Rosa' has the largest leaves of any cultivar and has a spreading habit that grows to 25 feet tall and 20 feet wide. It is best in zones 6 to 9.
- 'Northern Belle' is reliably evergreen through most of zone 4. It grows to 20 to 25 feet even in the North.
Make sure to verify hardiness ratings before purchasing your sweetbay magnolia. Some are only hardy to zone 6.
Pruning should be done when trees are young, soon after they are established at around the two-year mark. Older trees are drastically more sensitive to pruning than young trees. As you shape the tree, try to thin out crowded branches to allow sunlight and air to reach inner limbs.
Sweetbay magnolias are best pruned immediately after their flowering period has concluded. Most cultivars have a tendency to grow multiple stems, and a common pruning strategy is to prune away all but the strongest stem, which will serve as a central leader and give the plant a more tree-like shape. The best time to prune is immediately after the flowering period is complete, though diseased or damaged limbs should be removed whenever they appear. Avoid removing multiple large limbs in the same season, but if you must do this, it is best done when the tree is still young.
Propagating Sweetbay Magnolia
Sweetbay magnolia is relatively easy to propagate from softwood cuttings. Here's how to do it:
- Using sharp pruners, cut 6- to 8-inch sections from the tips of young, green stems. Place them immediately in a jar of water to prevent them from drying out.
- Remove all leaves, except for two at the tip of each cutting.
- Fill a 10- to 12-inch deep plastic container with good drainage holes with a rooting medium—a good choice is a 1:1:1 mixture of peat moss, sand, and vermiculite.
- Plant each cutting in its pot, deep enough to hold it upright. Tamp the growing medium down around the stems, and moisten.
- Cover the pots with plastic and set them in a bright location, but not in direct sunlight. Within a few weeks, the cuttings should develop a good network of roots. Uncover the pot and continue to grow the specimen until it is large enough to plant in the landscape.
How to Grow Sweetbay Magnolia From Seed
Sweetbay magnolia is also relatively easy to propagate from seeds collected from the seedpods that fall from the trees in fall, but you'll need to be patient, as seedlings started this way may take as much as 15 years to grow into flowering trees. If you want to try it, collect the seedpods in the fall once they are dry on the branches. Let the pods fully dry, then break them apart and collect the small red seeds inside. The seeds should then be scarified by scrubbing them with a damp paper towel to remove the red coating. Then lightly scuff the seeds with fine sandpaper.
Store the seeds over winter at a temperature of 40 to 45 degrees Fahrenheit. Storing them in the refrigerator, packed with some moist peat moss, works fine.
Once outdoor temperatures reach 70 degrees, you can plant the seeds 1/2 inch deep in the desired garden location. Or, you can start the seeds indoors in late winter in pots filled with potting soil. Keep the sprouting seedlings moist as they are developing. Young plants should be sheltered from direct sun for their first year. Many people choose to grow magnolia seedlings in the pot for the first full year or two before planting them in the landscape.
Potting and Repotting Sweetbay Magnolia
Smaller cultivars of magnolia can make successful potted specimens for a deck or patio. If possible, choose a large container, several times wider than the root ball of the nursery-grown tree; make sure the container has good drainage. A standard peat-based potting soil is generally fine for sweetbay magnolia, but you will need to water quite frequently for this bog-loving specimen. Repotting should not be necessary for several years, until the root ball completely fills the container. More regular feeding is required for container-grown magnolias, as nutrients are quickly leached out from frequent watering.
During the winter months in cooler zones, pad the roots with several inches of mulch to protect them from frost. No winter protection is really required in warmer climates, but keep the ground free of debris which can harbor fungal spores and insect larvae.
Common Pests and Plant Diseases
The sweetbay magnolia tree is typically free of diseases, though you may see some fungal leaf spot develop from time to time. Fungal diseases on mature trees usually aren't serious, though they can be treated with copper-based fungicides. Be more diligent about treating fungal disease on young plants as they are becoming established.
When it comes to pests, scale and tulip tree leaf miners tend to be the most common annoyances, but these pests rarely cause serious damage. Pests can be controlled to some degree by using neem oil or another horticultural oil. Try to avoid using pesticides since these may also kill the parasitic wasps that are natural predators of leaf miners.
How to Get Sweetbay Magnolia to Bloom
A sweetbay magnolia that fails to bloom has usually experienced damage to the emerging flower buds from a spring cold spell. It is most likely to happen in northern zones where the tree's hardiness is somewhat borderline, but it can also happen when an unusual cold snap hits in warmer zones. This is usually not a problem, as the tree generally returns to a normal bloom pattern the following spring.
Magnolias can also fail to bloom if they are being fed with a high nitrogen fertilizer, which stimulates foliage growth at the expense of flowers. And if they are planted in soil that is too alkaline, your magnolia may withhold blossoms.
Common Problems With Sweetbay Magnolia
Sweetbay magnolia doesn't have a lot of issues, but you may notice these:
It's common for a magnolia to turn yellow if it is planted in alkaline soil. These are acid-loving plants that need a low pH in order to properly absorb nutrients. Yellowing leaves, called chlorosis, occurs because the plant is unable to absorb the nutrients it needs. Try feeding the plant with an acidifying fertilizer, or amend the soil with peat moss or pine needs to lower the pH.
Leaves Turn Brown in Summer
It's natural for magnolias to turn brown and drop their leaves in fall, but if it happens in spring or summer, it is usually because the tree is not getting enough water. Remember that this type of magnolia likes boggy conditions, and you may need to water several times a week during hot spells.
Late, hard frost in the spring can also damage leaf buds and cause the emerging leaves to be dry and brittle. The tree generally recovers easily from this damage.
Rough, Bumpy Patches on Twigs and Leaves
This is the tell-tale sign of scale insects infesting your tree. Minor infestations are rarely serious, but a widespread scale attack should be treated with neem oil or another horticultural oil.
How long does a sweetbay magnolia live?
You can expect 80 years or more from a sweetbay magnolia that remains healthy and is growing in ideal conditions. Potted specimens may need to be abandoned after 10 to 15 years as they become too big to be effectively grown this way.
How can I use this tree in the landscape?
Because most cultivars have an upright, somewhat columnar shape, this is a good magnolia to use where space is limited, such as in narrow spaces between buildings. It's fondness for boggy conditions makes this a good tree for problem low-lying areas of the landscape. Its brilliant flowers make it a good specimen tree in the yard, and it can also work well as a potted tree for patios.
What are some good magnolias for colder climates?
While there are some cultivars of sweetbay magnolia that are hardy into zone 4, there are better choices for cold-winter gardeners. Star magnolia (Magnolia kobus var. stellata) is reliably hardy in zone 4, and often survives even into zone 3. ‘Leonard Messel’ and ‘Merrill’ are hybrid cultivars, crosses between magnolia kobus and magnolia stellata; these, too, are reliably hardy in zone 4. The 'Little Girl' series of hybrids are hardy even into zone 3.
What are some good magnolias for my very small garden?
'Lillipution' is a cultivar of saucer magnolia (Magnolia x soulangeana) that grows only 12 feet tall. It is hardy in zones 5 to 9. Several cultivars of the 'Little Girl' series top out at only about 10 feet tall: 'Ann', 'Betty', 'Jane', 'Judy', 'Pinkie', 'Randy', 'Rickie', and 'Susan'.
'Genie' is a 13-ft.-tall hybrid cultivar with dark pink flowers. 'Jane Platt' is a 15-foot cultivar of star magnolia (Magnolia stellata).