Stella Otto: The Backyard Fruit Gardener

Today's Tip: Mow vegetation short around the base of fruit trees and bushes to reduce winter habitat for rodents.

Pollination — A Sexy Time in the Fruit Garden

Per­haps you expected that this arti­cle was going to be as excit­ing as Adam and Eve in the gar­den of Eden. Well, maybe not as excit­ing, but surely as impor­tant! It will address the fine points of how we’ll get from blos­som to fruit crop. Numer­ous fac­tors can make the process go awry. Your under­stand­ing of the pol­li­na­tion process can help achieve a boun­ti­ful har­vest. Two impor­tant points to remem­ber that apply to all edi­ble fruit plants:

  1. Bees and other pol­li­nat­ing insects rarely carry pollen to plants at a great dis­tance. Hence it is highly ben­e­fi­cial to plant tree fruit vari­eties within 100 feet or less of each other. Nuts and berry bushes do best when within 50 feet of a pollen source.
  2. Bee flight is severely cur­tailed below 65°F. This can result in lim­ited to no pol­li­na­tion and a reduced fruit crop.
Does Your Fruit Tree Need a Partner?

The pro­duc­tion of flower buds alone is not enough to insure pro­duc­tion of a suc­cess­ful fruit crop. It is really only the first step. Once the bloom is vis­i­ble, the crit­i­cal processes of pol­li­na­tion and fer­til­iza­tion are start­ing to take place. Pol­li­na­tion is the trans­fer of pollen from the male parts of a flower blos­som to the female parts. To com­pli­cate mat­ters, a num­ber of dif­fer­ent fruit vari­eties have pollen that is not com­pat­i­ble with itself, the vari­ety that is pro­vid­ing the pollen. This is the case with apple, pear, most sweet cherry, Japan­ese plum, non-astringent ori­en­tal per­sim­mon, blue­berry, and kiwifruit.

For exam­ple, most apple vari­eties need to be pol­li­nated with pollen from a dif­fer­ent apple vari­ety. This con­di­tion is known as being self-unfruitful. A Red Deli­cious apple will not suc­cess­fully pro­duce much fruit if pol­li­nated by another Red Deli­cious. How­ever, if that same Red Deli­cious blos­som receives pollen from a McIn­tosh bloom, it will most likely develop a nice crop of fruit (other nor­mal con­di­tions coop­er­at­ing.) This process of shar­ing pollen between vari­eties is known as cross-pollination.

Sweet cherry, will chal­lenge you a bit more. Not only is it self-unfruitful; there is also some cross-incompatibility between cer­tain related sweet cherry vari­eties. That is, not all vari­eties of sweet cher­ries will pol­li­nate all other vari­eties. So you must choose from vari­eties of suf­fi­cient genetic vari­a­tion — one from group A and one from group B, as it be. Most nurs­eries offer cross-pollination charts in their cat­a­logs indi­cat­ing appro­pri­ate choices. If you are extremely short on gar­den space, two vari­eties of sweet cherry, Lap­ins and Stella, are self-fertile and do not require cross-pollination by another variety.

Time to Tango — or Bloom

In addi­tion to tak­ing cross-pollination needs into account, it is equally impor­tant to pay atten­tion to when the var­i­ous vari­eties bloom. The time that the receiv­ing bloom of one vari­ety is open needs to coin­cide closely with the time that the pol­li­nat­ing vari­ety is also bloom­ing. Oth­er­wise, proper pollen trans­fer and fer­til­iza­tion will not take place. Fer­til­iza­tion occurs when the male and female genetic mate­r­ial are united to form an embryo which can then develop into the fruit.

Bloom is typ­i­cally thought of as early, mid-season, or late bloom­ing. (Note: this does not nec­es­sar­ily cor­re­late with the matu­rity sea­son of the fruit.) It is best to choose two or more vari­eties from within the same group, but it is pos­si­ble to choose one vari­ety from the early group and one from the mid­dle bloom­ing group as their bloom time will often over­lap some­what. If you choose one vari­ety from the early group and one from the late how­ever, their bloom times will likely be too far apart to pol­li­nate each other well.

Some fruit do not require cross-pollination and are termed self-fruitful — notably apri­cot, Euro­pean plum, tart cherry, peach & nec­tarine, fig, quince, astrin­gent per­sim­mon, black­berry, cur­rant, goose­berry, rasp­berry, straw­berry, and per­fect flow­ered muscadine.

To Each His Own

Beyond the gen­eral con­sid­er­a­tions of pol­li­na­tion some fruit have a few indi­vid­ual quirks.

  • Apple — There is a small per­cent­age of apple vari­eties that, due to pecu­liar­i­ties of nature, have a triploid num­ber of chro­mo­somes. As a result, their pollen is ster­ile. Although they can be suc­cess­fully pol­li­nated by other vari­eties, they can­not them­selves serve as reli­able pollen sources for other vari­eties. If you do want the fruit from one of the vari­eties listed below, be sure that your fruit plant­ing is made up of at least three apple vari­eties, includ­ing those with viable pollen.
    Triploid vari­eties include Arkansas Black, Bald­win, Belle de Boskoop, Bram­ley Seedling, Graven­stein, Jon­agold, Mutsu, R.I. Green­ing, Sir Prize, Spigold, Stay­man Wine­sap, Sum­mer Rambo, and Winesap.
  • Kiwifruit — Unlike most other cul­ti­vated fruit, kiwifruit have some plants that bear male flow­ers and other plants that bear female flow­ers. Although flow­ers on either type of plant will have both male and female repro­duc­tive parts, only one repro­duc­tive struc­ture is func­tional in each case. Nor­mally the female flower is slightly larger in size than the male flower, mak­ing it pos­si­ble to visu­ally dis­tin­guish between the two. It is best to have a male flow­er­ing kiwifruit vine within twenty feet, and def­i­nitely no fur­ther than thirty five feet, away from any given female vine. As a rule of thumb, a ratio of plant­ing one male per six female vines is rec­om­mended. Of course if you only want one female, you will still need a male plant too.
  • Mus­ca­dine grape — While bunch grapes are self-fertile, this is not the case with all mus­cadines. Many of the newer vari­eties are self-fertile; but many of the old vari­eties are pis­til­late, or female. Con­se­quently, they need to be planted together with a pol­li­nat­ing vari­ety. For the best pol­li­na­tion, plant at least two self-fertile vari­eties within fifty feet of any pis­til­late vari­ety. Among the pop­u­lar pis­til­late vari­eties are Black Beauty, Fry, Sweet Jenny, Sug­ar­gate, Sum­mit, and Supreme.
  • Peach — A few vari­eties of Hale parent­age break the norm. Early Hale, Hale­haven, and J.H. Hale are self-unfruitful; nei­ther pol­li­nat­ing each other nor able to be pol­li­nated by Elberta.

Regard­less of the indi­vid­ual quirks, there are hun­dreds of fruit vari­eties, mak­ing it pos­si­ble to find a part­ner for just about any­thing you might want to grow.

©2013. Adapted from the Back­yard Berry Book: A hands-on guide to grow­ing berries, bram­bles, and vine fruit in the home gar­den and the Back­yard Orchardist: A com­plete guide to grow­ing fruit trees in the home gar­den by Stella Otto.