Stone Fruits

Plums, nectarines, apricots, cherries, peaches, and almonds are all stone fruits. But, so are olives, coconuts, mangoes, pistachios, and black pepper! So what, exactly, are stone fruits?

Nectarines

What are stone fruits?

The term stone fruit refers to all plants that produce hard pits, called drupes. Drupes are indehiscent fruits, which means that they do not split open. Drupes have an outer part (pericarp) that is made up of a skin (exocarp), flesh (mesocarp), and a coating (endocarp), that surrounds a single seed, or kernel. That seed is also known as a stone, or pit. Botanically, stone fruits are those that develop from a single carpel. Drupes are close cousins to berries, but that’s another story. A more common definition of stone fruits refers only to members of the Prunus genus.

Diagram of a typical drupe, or stone fruit (LadyofHats) Public Domain

Prunus plants

The Prunus genus is part of the rose family, making plums, almonds, and all the rest distant cousins to loquats and soapnut trees. [Did you know that almonds, nectarines, and peaches are the same species? I didn’t either.] There are both edible and ornamental stone fruits. Hawthorn, flowering cherries, and cherry laurels are ornamental stone fruits, but I much prefer investing time, water, and garden space on plants that produce food. When that food happens to be summer sweet peaches and apricots, well, all the better! The fruit of Prunus can be loosely or firmly attached to the seed, hence the terms freestone or cling varieties. Most stone fruits contain compounds which, when chewed up, generate hydrogen cyanide, but don’t let that scare you off. This is mostly true of the seeds, not the fruit, and the amounts are too small to do anything but fuel sensationalists.

Propagating Prunus

If you plant the pit from a grocery store stone fruit, you probably won’t get offspring that looks, behaves, or tastes the way the first fruit did. This is because most bare root fruit and nut trees available today are a hardy rootstock grafted onto a productive, flavorful fruit producer. Many of these plants are propagated by twig scions and cuttings taken from adventitious roots, to create clones. Because all of these fruit trees are members of the same genus, they can be grafted onto one another and produce edible fruit. One variety of grafted tree, in particular, boasts 40 different types of stone fruit on the same tree! These botanical masterpieces are created by New York artist Sam Van Aken. He calls them Tree of 40 Fruit. You can find similar stone fruit trees, with 4 or 5 types of fruit, available in garden centers and catalogs. These are a great way to make use of a small space.

How stone fruits grow

Members of the Prunus genus are all perennial trees and shrubs descended from a Eurasian ancestor. As such, these trees are best suited to northern temperate regions, or climates with four seasons. If you want grow these productive, rewarding trees, be sure to select a variety that has a chilling hour requirement that matches your microclimate, otherwise, you might not get any fruit. Adding a stone fruit tree to your landscape is a lovely way to enjoy spring blossoms and summer fruit. There are many dwarf and semi-dwarf varieties that don’t take up a lot of room, and some can even be grown in large containers.

Caring for stone fruits

When you first get a bare root tree, you will need to select a site with lots of sunlight and good drainage. Dig a hole slightly wider than the spread out roots and as deep as the roots go. There is no need to dig any deeper or wider. If your soil is heavy clay, be sure to rough up the edges of the hole a bit, to make it easier for young roots to penetrate. Cover the roots with soil, making sure that the soil level is exactly the same as it was before, relative to the tree’s trunk. Covering the graft area or trunk with soil can lead to rot and death of the tree. Water it in well, gently tamping down the soil to remove large air pockets that would allow the roots to dry out.

It is a good idea to provide a tree support for your young tree. The first year or two, you can improve long term production by removing spring blossoms. This frees the young tree to focus its resources on developing a strong root system. As the tree becomes better established, it is still a good idea to thin fruit for better size and flavor.

Whitewash the trunk and exposed branches each spring with one part white, interior latex paint and one part water to prevent sunburn damage. Each spring and summer, stone fruit trees should be fertilized and irrigated properly, depending on the species, tree size and condition, and local weather.

​Most stone fruits are deciduous, which makes tree training and winter pruning much easier. The only exception is apricot trees, which should be pruned in summer, due to the threat of Eutypa dieback. 

Dormant nectarine tree, whitewashed and caged

It is not unusual for a protective gummy sap to appear at pruning cuts and other wound sites. While these trees are dormant in winter, they are sprayed with dormant oil, to break the disease triangle of many common pathogens.

Corking (dried out fruit) can be prevented by making sure that the soil contains enough boron and calcium. Before adding soil amendments, be sure to get a soil test from a local, reputable lab. Over-the-counter kits are not yet effective enough to be useful. Properly maintained, Prunus trees are classified as low flammability plants, making them a fire safe addition to your landscape.

Pests and diseases of stone fruits

While each species has its own set of problems, most stone fruits must deal with attacks by aphids, mites, caterpillars, shot hole borers, glassy-winged sharpshooters, San Jose scale, Eutypa dieback, peach twig borers, naval orangeworms, mealybugs, and cucumber beetles. Diseases of stone fruits include cane blight, shot hole fungus, crown gall, brown rot, bacterial spot, peach leaf curl, and bacteria blast. Stone fruit trees use idioblasts to protect themselves, and you can apply fixed copper, sulfur, or Bordeaux mixture (Bt), each in their own way and time, to aid in protecting your stone fruit trees. [Never use sulfur on apricots.] Netting and tree cages can help protect the fruit from birds and squirrels, and sticky barriers are an excellent way to thwart crawling insects.

​The shear volume of fruit that a single stone fruit can produce makes them an excellent choice for the home garden. When harvesting your crop, remember than these fruits produce ethylene gas, which which ripen everything nearby.

Add stone fruits to your foodscape for years of sweet summer deliciousness and beauty.