How to Grow and Care for Star Magnolia

Star magnolia is a slow-growing, flowering shrub with a rounded growth habit that can be shaped into a multi-stemmed shrub in a pyramid. The star shape of its white flowers gives it both its common name and scientific name. It thrives in sunny, mild conditions in loamy, moist soil, flowering in late winter/early spring.

Star Magnolia Care

Though star magnolia is native to Japan, it grows in USDA planting zones 4 through 9. Here are the main care requirements for growing star magnolia:

• Select a well-drained site that is located in full sun to partial shade.
• Plant in soil that is in the acidic to neutral range.
• Water somewhat regularly during the plant's first couple of years.
• Protect the plant from heavy snow and ice, though they can tolerate below-freezing temperatures.
  
• Consider lightly applying an all-purpose fertilizer in spring, but this plant won't need regular feeding.

Light

This tree grows best in full or partial sun, needing at least four hours of direct, unfiltered sunlight daily.

Soil

Star magnolia likes to grow in loamy, well-draining moist soil. The plant can grow in both neutral and acidic soils.

Water

Star magnolias are low-maintenance plants that don't require frequent watering. They can handle some flooding and are tolerant of moderate drought situations. Water magnolia trees thoroughly once a week during the first two growing seasons and twice a month in subsequent years.

Temperature and Humidity

Star magnolia is cold hardy down to zone 4 or as cold as -30 degrees Fahrenheit. However, it can be damaged by heavy snow and ice, particularly its blossoms can be injured by frost or wind. Its humidity needs are moderate, at about 30 to 50 percent.

Fertilizer

Star magnolia needs very light to no fertilizer. Apply a general, all-purpose fertilizer in early spring before any growth appears. Get a phosphorus-rich fertilizer to promote stronger root growth and potential bloom production. For the amount to use, follow product label instructions.

Types of Star Magnolia

Star magnolia has a variety of flower colors (ranging from white to pink), tree sizes, and shapes.

• 'Centennial': Features large 5-inch flowers; white with a slight tinge of pink on the outside, can grow up to 25 feet tall.
• 'Rosea': Pink flowers that fade to white at maturity; non-fragrant.
• 'Royal Star': Double, white flowers form from pink buds; grows up to 12 feet tall.
• 'Pink Stardust': Fragrant, 5-inch flowers; tree is pyramid shape; grows up to 12 feet tall.
• 'Waterlily": Highly fragrant; may flower later than other star magnolias.
• 'Jane': Grows about 15 feet tall; large 8-inch blooms; burgundy-purple buds with tulip-shaped flowers; pink petals on the outside and white inside.
  

Pruning

The plant blooms on old wood (last year's growth), so prune it more or less immediately after blossoming to avoid losing next year's flowers. People don't generally prune magnolias much (although M. stellata is sometimes a bit more tolerant of pruning than other members of its genus).

They have a tendency to grow as multi-stemmed shrubs or bushes. If you wish to avoid this look, prune away any suckers to train your specimen to assume a tree form. Prune away the lower growth as it emerges while letting the rounded, spreading crown become dense.

New growers are sometimes alarmed by the "funny growths" that appear on star magnolia trees in the latter part of the growing season. No need to worry, though: Those odd lumps are just the pods in which star magnolia tree seeds are contained.

Propagating Star Magnolia

The best way to propagate star magnolia is by stem cuttings in late spring or early summer from soft or semi-hardwood. If using a rooting hormone, roots will grow in a few weeks. Star magnolia can also be grown from seed.

You will need to grow the rooted cutting in a pot for a year under controlled conditions before planting it in the ground. Using stem cuttings from annual pruning benefits star magnolia when branching gets crowded. Here's how to propagate a star magnolia using stem cuttings:

1. You will need a planter or pot with drainage holes, a perlite potting mixture, sterilized pruners or a knife, and a clear plastic bag. Optionally, get compost and rooting hormone.
2. Cut a 6- to 8-inch branch with active growth, cut on a diagonal, or cut a vertical slit at the bottom. Optionally, add rooting hormone to the cut end to encourage rooting success.
3. Plant the cut end about 2 inches deep into the perlite potting mix. Optionally, add compost to the mixture to encourage growth. Moisten the soil. Tent a clear plastic bag over the planter to trap moisture in the bag, which encourages rooting.
4. Put the plant in indirect light. While waiting for roots to grow, keep the top of the soil moist. Remove the tented bag once you notice growth—a sure sign of successful rooting.

How to Grow Star Magnolia From Seed

Magnolia seeds must go through stratification or a cooling period to germinate.

1. Place the seeds in a container of moistened sand in the refrigerator for three months. When you remove the seeds from the cold, it triggers the seeds to germinate.
2. Plant the seeds about 1/4-inch deep in a pot or the ground in the spring using potting soil. Mulch over the plant to keep moisture in the soil. Place it in a sunny spot.
   
3. Transplant the seedling after about one year of continuous growth in a controlled environment. The planting hole should be at least three times the width of the root ball or container and just as deep.
4. The root ball should be even with the ground when placed in the hole. Be sure the plant is straight before replacing half of the soil you took from the hole.
5. Fill the hole with water and allow the root ball to absorb the moisture. Backfill the hole with the remaining soil.
6. Top dress with a layer of mulch to keep the roots moist and discourage weed growth. Dress with compost in late winter.

Common Pests and Plant Diseases

Star magnolias are susceptible to fungal infections like powdery mildew, botrytis (gray mold), verticillium wilt, and leaf spot. It spreads by spores between infected plants.

To prevent conditions that favor fungal growth, give the plant ample sunlight, air circulation, and well-draining soil, and make sure the tree has dry foliage and flower petals. Also, remove infected leaves early on. Prune branches or thin them out to discourage an overly moist environment and promote air circulation. If symptoms persist, treat with fungicides according to the product label instructions.

Magnolia scale insects are one of the biggest threats to star magnolias. The insects suck the sap from the leaves and can harm the tree. The insects leave behind a residue that leaves a black, sooty mess, which encourages mold growth conditions.

To treat the magnolia scale, you must catch it early on when the insect is in the crawling stage. You can use organic methods like horticultural oil or insecticidal soap (usually applied in August) and reapply again two weeks later. Progress to other chemical alternatives if organic methods are unsuccessful.

How to Get Star Magnolia to Bloom

Bloom Months

Depending on your USDA growing zone, star magnolias bloom from late February to early April.

What Do Star Magnolia Blooms Look and Smell Like?

Star magnolia blooms usually have showy 12 to 18 thin, delicate, strap-like petals that are whitish or pink-toned. Depending on the cultivar, some star magnolias have up to 30 petals. Many types are sweetly fragrant, while some have no scent at all.

How to Encourage More Blooms

If your plant is mature enough or has flowered in the past, check its soil; most magnolia trees prefer acidic soil. Full sun is also a general prerequisite for bloom creation.

Deadheading Star Magnolia Flowers

Star magnolia will shed their flowers naturally with no deadheading assistance necessary. If your star magnolia was grown from seed, it could take your seedling up to 15 to 20 years for it to mature enough to the point of flower production.

Common Problems With Star Magnolias

Star magnolias are easy to plant, and their care is straightforward. They are relatively trouble-free, except for being susceptible to fungus and scale if the branches are overcrowded or not getting enough ventilation.

Tiny Brown or White Bumps on Branches

A sign of star magnolia infested by magnolia scale is brown or white bumps clustering on branches. The plant's leaves appear shiny and sticky and often look like they have black sooty mold growing on the plant. If not treated or the insects overtake the plant, the tree will not survive. To get rid of magnolia scale, manually remove the insects or the affected limbs or branches, or use organic or chemical controls like horticultural oil, insecticidal soap, or pesticides.

Brown or Black Leaf Spots

Several fungus types can cause leaf spots that appear black, brown, tan, or red. Leaf spot is most likely to occur during rainy or humid weather and often clears up when sunny, dry weather returns. Remove diseased brown leaves that have dropped, preventing the fungus from spreading. Most mature trees can fight it independently, but a young tree might need help from a copper-based fungicide before being ravaged by the fungus.

Dying Branches

Verticillium wilt is a fungus that can kill branches or an entire star magnolia. Symptoms include streaking and fading wood, leaves dropping prematurely, and weakening limbs. Once a plant gets verticillium wilt, spores remain on the tree, infect the soil, and can spread. Mature trees can likely fight it off for a few years, but the prognosis is grim; eventually, it will kill the tree. Removal is the best course of action.