Plum trees are relatively easy to start from a pit if you have a little patience. However, like most fruit trees, they usually don't reproduce the same type of tree as that of the fruit. In order to produce trees that are true, professional growers propagate plum trees by grafting stems onto an existing rootstock. So be prepared for some surprises after planting your homegrown plum tree in the yard. Whether or not it will bear fruit is also unpredictable. Starting with two seedlings may improve the chance of getting fruit, since many varieties of plum require cross-pollination.
Slice the ripe plums open and remove the pits. Wash them thoroughly in lukewarm water to remove the excess pulp. Mix together a small quantity of equal parts peat moss and perlite, and fill the plastic bag. Add just enough water to moisten the mix, put the seeds in the middle of the bag, and seal it.
Store the bag in your refrigerator for about two months. This process, known as stratification, simulates the natural conditions that will bring the seed out of dormancy. The ideal temperature to stratify the pits is between 33 and 41 degrees. Your refrigerator will be close enough to that range to get the job done.
Check the pits after four weeks to see if they have sprouted. If not, continue checking each week, and remove the pits as soon as sprouts appear. It usually takes anywhere from 60 to 90 days for the seeds to sprout.
Prepare the potting mix by blending three parts potting soil with one part perlite. Fill your planting containers, and plant a seed in each one. The seeds should be about 2 inches below the surface of the potting mix and covered over. Add just enough water keep the potting mix moist. Place the pots on a tray in a sunny location such as a window sill.
Allow the seedlings to grow to 10 to 12 inches, and then transplant them to a well-drained spot in your yard that gets plenty of sunlight. Space them about 20 feet apart to allow enough room for the trees as they mature.