How to Grow and Care for Trident Maple

Trident maple (Acer buergerianum) is a smallish maple with a nicely rounded branching habit. Its three-lobed dark-green leaves are relatively small (1 1/2 to 3 1/2 inches wide) and turn rich yellow to red in the autumn. The exfoliating bark becomes quite striking as the tree ages, showing gray, orange, and brown colors. The bark color and texture adds a considerable amount of winter interest after the leaves have fallen.

Though the trident maple lacks the elegance and grace of the Japanese maple, it compensates by being fast growing, adaptable, and easy to maintain. (It is, however, less hardy than a Japanese maple and highly susceptible to storm damage.) Reaching a modest 25 to 35 feet in height at maturity, the trident maple is a good choice as an ornamental tree in a modern garden landscape and it will do well in most yard designs. Adapting the trident maple to fit your plans is a matter of pruning the tree at an early age to dictate if it will be multi-trunked or single-trunked.

Trident maple is usually planted as a potted nursery specimen or balled-and-burlapped plant in the spring or fall. It has a medium to slow growth rate, gradually slowing down as the tree ages. Early years may see this tree add 2 feet per year, but older trees will slow to about 1 foot per year.

Trident Maple Care

Trident maple will do best in average, medium-moisture soil in a sunny location, though it tolerate partial shade. Give it at least 24 feet of space to spread. Plant it in a well-prepared hole with loosened soil amended with plenty of organic material; it prefers slightly acidic soil. The hole should be at least twice as wide as the nursery container or burlap ball. Plant the tree at the same height it was growing in the nursery container.

Water weekly (and deeply) when the tree is young; after its first two years, a trident maple needs to be watered only during dry spells.

Light

The trident maple will do best in full sun. Giving it a full six to eight hours of sun a day will promote impressive foliage and shape. Shadier conditions will cause the tree to be leggy and sparse.

Soil

This tree is pretty adaptable when it comes to soil but thrives in moist and well-drained soil. Soil pH is somewhat of a concern and should be considered as this maple does best in neutral to slightly acidic soil. Testing the soil around the tree before planting and occasionally thereafter is wise. Amend the soil as needed if the soil is too alkaline.

Water

Until the tree is established, 15 to 20 gallons of water a week for the first season should be sufficient to keep a trident maple happy. After that time, you can water less frequently, as needed. This species tolerates occasional drought conditions.

Temperature and Humidity

The tree can cope with cold winter conditions, and will live longer where it has a reliable winter dormancy period. It does best in USDA Zones 5 to 9, but sometimes survives in the southern half of zone 4. Humid conditions can make the tree prone to fungal leaf spot diseases, though these usually are not serious.

Fertilizer

There is no reason to fertilize this tree other than if soil tests show the conditions to be too alkaline. This can indicate a need for an acidifying fertilizer or soil amendment.

Types of Trident Maple

Trident maple is available in more than 20 excellent cultivars offering different sizes, growth shapes, and leaf color. Some of the better selections include:

• 'Aeryn' is a good choice as a street tree or medium-sized landscape shade tree, growing to a maximum size of about 35 feet. It has excellent red, yellow, and orange fall color.
• 'Michael Steinhart' has leaves that are bright yellow. It is a smaller tree, achieving a maximum height of about 15 feet after 15 years.
• 'Mino Yatabusa' is a dwarf tree with long, narrow leaves. It matures to a maximum size of about 8 feet and has a spreading, shrubby growth habit. It can make an excellent container plant.
• 'Miyasama Yatsubusa' is another dwarf tree, reaching 6 feet in height but with a more upward growth habit than other dwarf varieties. In fall, the leaves begin with a bright yellow color that transitions to deep burgundy red.
• 'Streetwise^®' is a cultivar grown specifically for use as an upright street tree. It is more accepting of training as a single-trunk tree and turns brilliant red in fall. It is a somewhat larger specimen, sometimes achieving 45 feet. This is a trademarked cultivar that should not be propagated.

Pruning

Trident maple tends to naturally be a multi-stemmed plant, but when used as a street tree, it is often limbed to allow for a singular stem for upright growth. Trees grown as specimen plants, on the other hand, are often allowed to spread and keep their natural shape.

Pruning should be avoided when the sap is running in late winter and early spring. Many authorities recommend waiting until the tree has fully leafed out in summer before pruning, but it can also be done during the full dormancy of mid-winter. Pruning should involve removing dead, broken, or diseased limbs, as well as opening up the center of the tree to improve light penetration and air circulation. With trident maples, early pruning should involve removing competing leaders if your decision is to train the tree as a traditional landscape tree with a single trunk.

Trident maple is a very popular choice for the ancient Japanese art of bonsai, or its Chinese counterpart penjing. Though bonsai is much more prevalent, the art form of growing and sculpting miniature trees originated in China, where the trident maple is a native. The specialized and detailed art form of Bonsai pruning is generally done in the spring.

Propagating Trident Maple

There are a variety of ways to propagate a trident maple, but one of the easiest is root a stem cutting—a process that works with most non-grafted maple trees. This is best done in late spring as new growth is at a peak. Here's how to do it:

1. Fill some small containers with standard commercial potting mixed blended with well-decayed compost.
2. Cut several long pliable stems about 10 inches long from the tips of some young branches, snipping the ends at a 45-degree angle.
3. Cut away all the leaves except for a few at the top.
4. Dip the end of each cutting in rooting hormone, then plant them so about one-third of the cutting is buried in the potting mix. Firm the soil around the cutting and water it well.
5. Place the planted cuttings in a sunny location, but where it can be protected from full sun during the hottest part of the afternoon. Keep it well-watered.
6. After several months, the cutting should develop roots and you may see new leaf growth beginning. At this point, you can transplant the cutting into a permanent landscape location. Or, you can continue to grow the cutting in a container in a sheltered outdoor location until it is big enough to plant.

Remember that home propagation is only legal when you are attempting to propagate a non-trademarked cultivar or pure species. Trademarked cultivars such as 'Streetwise^®; cannot be legally propagated by any means.

How to Grow Trident Maple From Seed

The species form of trident maple is fairly easy to grow from collected seeds, but named varieties may not "come true" from the seeds they produce. And for trademarked cultivars such as 'Streetwise®', it is not legal to propagate them from seed. If you do have a variety that has viable seeds, collect the seed pods when they have turned brown or started to fall off on their own. Soaking the seed pods in water overnight will make it easy to peel them apart and extract the seeds inside.

Trident maple seeds require cold stratification, so place the seeds in a plastic bag with a mixture of moistened sand and vermiculite and place them in a refrigerator for three months (temps should be about 41 degrees Fahrenheit). Then, in early spring, plant them in small pots filled with ordinary potting mix, just barely covering the seeds, and place them in a warm location with plenty of direct sunlight, until they germinate and sprout.

Continue to grow them in their pots through the first growing season, then transplant them into their landscape locations in the fall. Or, the potted seedlings can be moved to a sheltered location for the winter, then planted in the landscape the following spring when new growth begins.

Potting and Repotting Trident Maple

Setting it permanently into the landscape is not the only option for the trident maple. These trees make fantastic candidates for large containers to place on patios or around the yard. They thrive in this setting and will not be hindered by the confined growing space, though the more extensive the container, the larger the tree. A heavy clay or cermaic container is best, as it will resist tipping.

If creating bonsai, penjing, or growing the tree in a container, it might be a good idea to shop for a dwarf cultivar. Acer buergerianum ’Miyasama Yatsubusa', for example, reaches a height of only 6 feet tall and has a spread of 3 feet, but, unlike the pure species, it is fast-growing.

Overwintering

In the first year or two, a young trident maple planted in the landscape should be well-watered going into winter. Do not feed your tree in the fall. Once established, a mature trident maple will display the best fall color if it is allowed to dry out somewhat in fall.

Young trees can be susceptible to gnawing rabbits and deer, so a shield of metal hardware cloth can protect them over the winter.

In cold regions, potted trees should be moved to a sheltered but unheated location for the winter, such as a shed or garage. Or, you can bury the pot in the ground up to the rim and cover the root zone with a thick layer of mulch.

Common Pests & Plant Diseases

Trident maple is a relatively trouble-free tree, but it can be prone to some of the same pests and diseases that affect maples as a group. Verticillium wilt, a fungal disease that causes the tree's vascular system to shut down, is a potentially life-threatening problem. Light infections can sometimes be halted by pruning out affected limbs, but a serious infection requires the removal of the entire tree.

The trident maple can also be susceptible to a variety of fungal leaf spot diseases, though these are rarely serious.

Common Problems With Trident Maple

Cultural problems are rare for trident maple, but in regions with heavy snow, limbs can sometimes break under the weight. With young trees, shake off snow after each snowfall to protect the tree.

Like other maples, trident maple grown in alkaline soil may develop chlorosis, which causes the leaves to turn pale green with darker veins. This is caused by the tree's inability to absorb nutrients. Amending the soil or using an acidifying fertilizer can lower the pH to create the acidic soil the tree needs.

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