Some plum cultivars are capable of self- pollinating and will produce fruit even if grown in isolation. Other plum varieties require cross pollination, which means at least two cultivars with overlapping bloom periods must be planted. The typical standard plum tree usually begins to bear fruit in three to five years and comes into full production in about 10 years. The average useful life of a plum tree is 15 to 20 years. Trees should be planted in early spring at least 20 feet apart in fertile, well-drained soil.
To determine a maximum maturity index (the stage at which fruit can be harvested without suffering bruising damage during postharvest handling) flesh firmness is measured with a penetrometer with an 8 mm-tip. Plums are less susceptible to bruising than most peach and nectarine cultivars at comparable firmness. Ideally plums should be stored at a temperature of 31-32oF with a 90- 95% relative humidity. Typical storage life is two to four weeks.
Source(s): Ohio State University Extension and UC Davis Postharvest website