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Mariposa plum, also called Improved Satsuma, is a Japanese blood plum tree that gives large, red to purple plums, sweet, juicy, and firm with a small pit. The flesh is a deep purple; the skin is tinted with a light green-color. The plums can be eaten fresh or cooked in a delicious, vibrant jam. The flavor is rich, lingering, and aromatic. We came across this plum tree by accident and have been enjoying the deliciousness of its fruit.
Growing a plum tree is simple as long as the tree is planted in the right soil and watered regularly. It grows best in warmer climates and blooms early spring. Harvest in the Pacific Northwest begins in September. If you live in a warmer climate, the tree will need approximately 250 hours of cool weather (between 32 degrees and 45 degrees (F) in order for it to go dormant and bloom in the spring—approximately 10 cool days.
Mariposas should be planted in the fall. They like a sunny spot with well-drained soil and lots of open space. Prepare the soil with plenty of organic compost or manure which will add nutrients to it and help it drain. Dig the hole about three times larger than the root ball. Mariposas are self-pollinating but if you plant two of them they will increase pollination and therefore fruiting. If you will plant two trees, keep the holes about 20 feet apart so they have room to grow. You will want the graft union (a lumpy scar that’s caused when the scion, a young shoot, and rootstock are united) positioned about 3 to 4 inches above ground level. To prevent air pockets around your roots, fill the hole half way, water it, and continue filling with the soil. Then mold and push down the soil around the top of the root ball with your hands. Water regularly until well established.
In the spring, it’s a good idea to fertilize the trees with a 10-10-10 fertilizer and then once more at the start of summer. Place a handful of the mix around the base of the tree and water it in really well. Speaking of watering, you want to make sure that the tree is getting at least one inch of water per week, unless it’s really warm, then you will need to increase the frequency to two to three times per week.
Pruning is important to know about though you won't want to do it too much in the first couple of years. The tree needs to reach its mature height of 14 feet to 18 feet before you prune it to your desired height. Pruning involves removing any branches that cross in the middle so that the main branches grow nicely with enough space around them that will allow room for the fruit, giving you more produce, and easier access to the plums themselves after they are ripe. Plum production begins when the three is 2 to 3 years old.
Eating the plums fresh is a pleasure; canning them will allow you to enjoy their deliciousness throughout the year. Here are the basics of canning mariposa plums.
You need canning jars, a stock pot and a jar lifter for removing the jars safely, a thermometer, a wide mouth funnel, a cooling rack, a wooden ladle and jar rings. If you haven’t done much canning, these are a few of the many useful tools available to use.
Plum Jam: Good with pancakes, toast, French toast, crepes, and pastries.
Begin by pitting the plums, chopping them, and coating them with sugar. For every pound of medium sized chopped plums you need 1/2 cup of granulated sugar and 1 teaspoon of lemon juice. If the plums are ripe and sweet, you may want to use less sugar than you would if the plums are not fully ripe and firm. The lemon juice will enhance the flavor of the plums though it is optional.
If making the jam at a later date, place the plum and sugar mixture in a sealed container and allow them to soften for 24 hours. You can do this for up to two days (place in the fridge if keeping it for longer than a day).
If you are choosing to make the jam the same day, run the plums through a food processor first, then add the sugar and mix well.
While the plum mixture could be cooked on the stovetop, (this will require your undivided attention since it can easily burn) I prefer to place it in a casserole dish and bake it in the oven at 325° for approximately 2 hours, checking it and stirring it occasionally. Once it has begun to thicken (liquid has evaporated through cooking), you will be ready to place the jam in sterile jars, making sure that the lids have been sterilized right before filling the jars. (You can bake for longer, if you would like the jam to have an even thicker consistency.) Cover the filled jars with the hot lids and screw the rings on tightly.
Processing the Jam
The National Center for Home Food Preservation has current canning guidelines here. We recommend these are followed.
Personal Experience with Processing the Jars of Jam
I have made jam using this method for many years without the additional water-bath method after the jars are filled with the boiling jam. Instead, after sealing the jars, I have placed them on my counter and covered them with a blanket to maintain the temperature of the boiling jam for as long as possible, and then left them undisturbed for 12 to 24 hours. This has proved successful in rendering sealed jars of jam (they pop within this time when they are sealed). If a jar does not properly seal, we use that jam right away.
According to the National Center for Home Food Preservation, "the high sugar content of fruit jams, jellies and preserves add an extra measure of safety and barriers to even spoilage." Though this method has worked personally, we recommend you use your own personal discretion in choosing the method that best protects spoilage and the safety of your family.