The Satsuma orange (Citrus unshiu) is one of the sweetest and most cold-hardy citrus fruits. Originating in China, the name "Satsuma" comes from the province in Japan where the modern cultivars originated. These fruits were first brought to North America in the 18th century. The small to medium-sized trees are low-growing with a spreading and droopy habit. The pretty white blooms appear in spring and are attractive to early pollinators.
With its loose, leathery skin, this is an easy-to-peel fruit with 10 to 12 segments of delicate and juicy flesh. Grown from seed, it can take up to eight years before you will reap your first harvest, but the timing will be significantly decreased if you plant a grafted tree—which is how it is normally sold commercially. For best results, plant your satsuma tree in early spring.
|Common Name||Satsuma orange, Satsuma, satsuma mandarin, unshu mikan, cold hardy mandarin|
|Botanical Name||Citrus unshiu|
|Plant Type||Evergreen citrus tree|
|Mature Size||10–15 ft. tall, 5–10 ft. wide|
|Soil Type||Rich, moist|
|Soil pH||Acidic, neutral|
|Hardiness Zones||8-11 (USDA)|
Satsuma Tree Care
When planting a satsuma tree, you should wait until the temperature remains consistently above 50 degrees during the day, for at least a week. This helps to ensure cold temperatures will not kill the plant in its vulnerable state and allows the tree to acclimate to mild temperatures before the heat of summer. If a hard frost does occur late in the spring season, cover the young sapling's branches loosely with a blanket to protect it.
Location is also important. Satsumas do not do well when exposed to wind, so in addition to choosing a location with plenty of sun, you will want some shelter provided by a building or a fence.
Most fruit trees require full sun conditions, and Satsumas are no exception. They should ideally get eight to 10 hours of direct sunlight, especially in spring during blossom and fruit formation.
Citrus trees prefer sandy, loamy soil with a slightly acidic pH. Satsumas are adaptable to different soil conditions such as rocks or clay, but will not tolerate salty or alkaline soils. The soil must have good drainage.
Satsuma trees need ample water, so plan on consistent and deep watering throughout the growing season. After planting, water every two to three days, and then once every week to ten days thereafter during the growing season. If you are experiencing a dry spell, watering will need to be more frequent to keep the soil moist.
Temperature and Humidity
Although Satsumas are more cold-hardy than other citrus trees, they still need consistently warm temperatures during their growing season. Cool (not cold) winters and hot, humid summers produce the best fruit harvest.
Mature trees can easily survive in short periods down to 14 degrees Fahrenheit during the winter. If temperatures dip lower than this, or if you have a young tree, implementing some cold protection strategies is recommended. Mounding the base of the trunk with around 2 feet of soil during these times can be beneficial (it should be removed again when the frosts pass). Alternatively, you could invest in a trunk wrap. Winter temperatures between 25 to 35 degrees Fahrenheit are actually said to enhance the sweetness of the fruits.
Satsuma trees benefit from regular fertilizing. It's best to fertilize in late January to early February when the tree is producing new growth. You may use a balanced 8-8-8 citrus fertilizer that contains nitrogen. A two-year-old tree can handle one to 1.5 pounds of fertilizer.
Types of Satsuma Orange
There are over 100 Satsuma cultivars to choose from. They can vary considerably in terms of when they mature, shape, color, and harvest quantity and quality. Some popular and readily available examples include:
- 'Owari': This productive tree produces high-quality fruit that rarely produces seeds
- 'Brown Select': This tree has a less droopy habit than most and has a dense, compact form. The rind easily separates from the flesh of the acidic, sweet fruit
- 'Silverhill': The shape of the fruit on this tree is flatter than most, and it has a high sugar and low acid content, making it particularly sweet. The tree is known for being vigorous and productive, with a more upright growth habit than most varieties.
- 'Early St. Ann': The fruit is ready for harvesting from mid-September through October—this is around a month earlier than most other cultivars.
Because Satsuma trees have a prostrate growth habit, pruning is essential to prevent fruit on low-lying limbs from touching the ground. The best time to prune your tree is early spring after the danger of frost. Prune any branches growing below 18 inches above the ground. Remove leaf debris from beneath the trees to help keep them clean and disease-free.
Propagating Satsuma Trees
Like most fruit trees, Satsuma trees sold commercially are usually grafted specimens, in which fruiting branches are grafted onto rootstock from another type of citrus, selected for its hardiness and disease resistance. Grafting is a delicate process that is difficult for amateurs, so citrus trees are usually not propagated outside the commercial industry. However, it is certainly possible to propagate a Satsuma tree by rooting a branch cutting. But be aware that the resulting tree is not likely to perform in the same way as the parent tree. If you want to try it, here's how:
- During the active summer growth period, use sharp pruners to clip several 4- to 6-inch branch segments, each containing a flexible green tip leading to firmer older wood. The cutting should have at least three sets of healthy leaves. Angle the cuts at 45 degrees.
- Remove the leaves from the lower two-thirds of the cutting. Dip the cutting in rooting hormone.
- Plant each cutting in a small pot filled with porous seed-starter potting mix. The bottom one-third of the cutting should be buried. Thoroughly moisten the potting mix, and press it firmly around the cutting to hold it in place.
- Place the cutting in a loosely secured plastic bag to hold in moisture, then place it in a location with bright, indirect light, at a temperature of 70 to 75 degrees Fahrenheit.
- Monitor the bagged cutting, moistening the potting mix when necessary. When the cutting has developed a good network of roots (you will feel resistance when lightly tugging on the cutting), loosen the plastic bag to allow the cutting to begin acclimating to drier conditions. It can take as many as six weeks or even longer for the cutting to develop roots.
- After several more weeks, when you see new green growth developing, the plastic bag can be removed entirely. Continue to grow the new tree in its container until it is large enough to transplant into the landscape or into a permanent patio container. It's not uncommon to grow the small tree in its starter container for a full year or more before transplanting it into the landscape.
How to Grow Satsuma Trees From Seed
It is no easy task to grow satsuma orange trees from seed, because the fruit is largely seedless (one or two seeds per fruit), and because it can take as much as eight years for the plants to mature into fruit-producing trees. Further, the resulting plant will likely look and behave differently than the parent tree, which is usually a grafted plant.
But if you want to try this method of propagation, peel open some ripe fruit and extract the seeds. You may have trouble finding them since satsumas are nearly seedless. Plant the seeds in small pots filled with a citrus tree potting mix, just barely covering the seeds. Moisten the potting mix, then place the post in loosely secured plastic bags and place them in a spot with very bright indirect light and warm temperatures (70 to 80 degrees Fahrenheit; you may need to use a heating mat).
Periodically mist the potting mix to keep it damp. Within 30 to 60 days, the seeds should germinate and sprout. When the seedlings are a few inches tall, remove the plastic covering and move the pots to a sheltered outdoor location where they will receive shade during the midday hours. Grow them in the original starter pots until fall, at which time you can transplant them into larger pots and move them to a sheltered location for the winter.
It's common practice to grow Satsuma trees in pots for several years before they are large enough to plant in the landscape. While they are in pots, move the plants to a sheltered location for each winter period.
Potting and Repotting Satsuma Trees
Although Satsuma trees can grow to as much as 20 feet tall, they can be trained to stay smaller and can be grown in containers. Keeping your mature Satsuma pruned to about 5 or 6 feet tall and wide is a good rule of thumb. Use a fairly large container, at least 20 gallons in size, and fill it with a commercial citrus tree potting mix. Any material will suffice for the container, though large black plastic container is a standard choice for growing citrus trees. Make sure the pot has ample drainage holes.
The main benefit of planting Satsumas in containers is that they can be moved indoors during the fall and winter. Placed near a sunny window and watered regularly (mist the leaves to keep the humidity up, as indoor heating has a drying effect), your Satsuma will produce tasty fruit for you during the cold months.
Repotting is typically required every three or four years, or whenever the roots begin to outgrow the pot and fill the drainage holes. When repotting, lift the plant out of its exiting container, prune back 2 to 3 inches of the roots, then repot in the same container with some added fresh potting mix. (You can also pot up to a container about 25 percent larger than the old pot, but eventually this may become impractical).
Potted Satsuma trees are often moved indoors to a sunny window in regions that experience regular freezing temperatures. These trees can survive temps down to 15 degrees Fahrenheit, but most growers take no chances when predictions call for extended below-freezing temps. In-ground trees can be protected with a frost blanket in regions where winter frost is common.
Withhold feeding during the winter months for young trees, but established trees more than two years old should be fed in late January or early February.
Satsumas are generally harvested between October and December, depending on the cultivar grown. The fruit doesn't do well hanging on the tree after maturity. Prompt picking when ripe is important, and they can then be stored in a refrigerator with temperatures between 32 and 36 degrees Fahrenheit.
As the fruit reaches maturity, the rind will become looser (separating a bit from the flesh), and the surface will become bumpier. The ripe fruit coloring can vary depending on the climate. In humid regions, the fruit may be ripe even while it is still green, and a reddish-orange hue is possible when night temperatures are cool.
Because the rinds are loose, it is best to clip the fruit from the tree rather than plucking. If you damage the rind when picking, it will lead to fast decay. Of all the citrus fruits, the satsuma is one of the most delicate, and care should be taken when handling it.
Common Pests & Plant Diseases
Although Satsuma trees are hardy compared to some other citrus varieties, they can be prone to a fungal disease called sour orange scab. This causes lesions on leaves, branches, and fruit. Thankfully, it doesn't usually affect the quality of the fruit flesh. Other fungal diseases are also possible, all best treated with a preventive fungicide spray.
Mites, scale, mealybugs, leafminers, and aphids are all possible insect pests, though Satsuma is somewhat more resistant to insect damage than other types of citrus.
How to Get Satsuma Trees to Bloom
The fragrant white blossoms of satsuma trees normally appear in early spring, from March to April. The green fruit becomes evident in August, turning orange in late September through December.
When a Satsuma doesn't flower or produce fruit, it is most often because the tree is not getting enough direct sunlight. These trees need at least eight hours, and preferably more, in order to produce robust flowers and fruit.
A lack of nutrients can also compromise the blooming period. Mature trees need a hefty feeding in January or February to support bud development.
Common Problems With Satsuma Trees
Satsuma is susceptible to some of the same fungal diseases common to other types of citrus (see above). In addition, Satsuma and other citrus species can be susceptible to chlorosis if grown in soil that is too alkaline. The main symptom is leaves that develop a light green color, often with darker veins. Take steps to lower the soil pH to a more acidic level to rectify this problem.
The other common complaint is from growers who take the "cold resistant" label too literally. Although these trees can survive an occasional cold snap down to 15 degrees Fahrenheit, they are by no means tolerant of extended cold. In borderline regions, it is all too common for trees to experience branch die-back when cold winter temperatures kill off the branch tips. Fortunately, it's an easy matter to prune off these damaged branches. Unless the cold spell is prolonged, Satsuma trees usually survive in zones 8 to 11. Even zone 7 gardeners can succeed with this plant if they're willing to move potted trees indoors when the weather turns cold.
Is Satsuma orange a type of mandarin?
Under some classification systems, Citrus unshiu is considered a species in its own right. Under others, they are considered to be a variety of mandarin. Genetics show the fruit is actually a mandarin-pomelo hybrid.
The satsuma is similar in size to its mandarin (Citrus reticulata) relatives, but it has a softer, more delicate texture and a looser rind, and it is ready to harvest earlier too.
How long does a Satsuma tree live?
Provided it remains disease-free, a citrus tree like Satsuma lives, on average, about 50 years. But under ideal circumstances, lifespans of 100 years or more are possible. Potted trees usually experience a somewhat shorter lifespan, mostly because they are more susceptible to disease and insect problems.