The number of hives needed to pollinate a tree fruit crop depends on the species of tree, the density of planting, and other conditions.
Successful pollination depends not just on the number or quality of the hives. Results will differ, depending on the characteristics of the orchard.
Most tree fruits require cross pollination from other varieties. The availability of these cross pollinators will affect the ability of the bees to adequately pollinate a crop. The cross pollinator should be close to the trees needing pollination and have a similar bloom pattern.
The denser the planting, the more blossoms need pollinating, and the greater the number of bees required. A very dense trellised planting may also require different hive placement because bees will not fly though or over the trees if they are too close together. If hives are placed on a road, preferably in the middle of the orchard, the bees will use the road as a flyway and from there will go up and down each individual row. The denser the planting and the longer the rows, the more bees it will take to fly the full length of the row and pollinate the entire orchard.
Type of fruit
Different tree fruit species require different amounts of bees to ensure pollination.
Cherries: Bing cherries are not hard to pollinate if there is good weather and cross pollen is available. Bing cherry blossoms have to be pollinated in the first 24 hours that they are open. The blossoms last for several days, but the longer they are open before pollination the more likely they are to slough off. Cross-pollinator varieties are critical for Bing. Rainier is a marginal cross pollinator because of differing bloom dates. Van, Black Republican, and other varieties are better cross pollinators and if intermixed in sufficient quantities will greatly enhance pollination. While Bing requires the largest number of bees to pollinate, Sweetheart requires the least. All other varieties are between the two. How many colonies you choose to put in depends on your comfort level. For cherries, my comfort level is never less than five hives per acre. During bloom and bee flight weather, I walk through my [cherry] orchard, and if I don’t hear a constant buzz, I add more hives.
Pears: Pears are another difficult crop to pollinate. Many growers believe that bees do not like pears. Actually, the bees will store more pear pollen than any other tree fruit. When the blossom first opens, the pollen grains are pink, and the bees will not be on the blossoms. Depending on the temperature, the pollen will then turn to a tan color, and the bees will be frantically collecting and storing it. In the final phase, the pollen grains turn to a dark brown to gray, and the bees will no longer be seen.
During a cool to moderately cool season, the pear blooms are staggered in opening so the pollination period lasts several days. During a hot year, the pear pollination may be over in hours. In these hot years, I have been told by growers that the bees did not pollinate their pears. I take the hive apart and look at the combs and observe slabs of pear pollen stored in the hives. The pollination window was so short that growers did not observe the bee flight. However, the pears were successfully pollinated, and these growers will have a crop.
Another reason growers do not see as many bees in the pear trees is that pears produce no nectar. Some bees are pollen gathering and others are nectar gathering. In pear pollination, all nectar-gathering bees are elsewhere. Usually, only pollen-gathering bees will be found in pears.
The question of how many hives to place on pears depends on each individual grower’s comfort level. Pears are often in very dense plantings which increases the number of blossoms per acre to be visited. In my pears, my comfort level is two hives per acre minimum, and in my denser pear walls, I use four hives per acre.
Apples: Apples are probably the easiest tree fruit crop to pollinate. If 10 to 20 percent of the bloom is pollinated, there will be a sufficient crop. Tree density is an issue. Different varieties are harder to pollinate than others. Golden Delicious, Gala, and Jonagold are typically the easiest. Red Delicious and Fuji are in the middle, and Granny Smith and Braeburn are probably the most difficult. The number of hives to set depends on your comfort level. Many growers are using one-half hive per acre and achieving adequate pollination, while others are not comfortable with less than 1.5 to 2 hives per acre.
Bees require a great amount of water when they are raising brood. The best source for water is from mud or a sprinkler spigot left leaking. Buckets are an acceptable source of water if nothing else is available. A piece of burlap placed in the bucket, will provide a landing place for the bees, so they will not drown when attempting to get water. Be careful of the spray filling station in your orchard. Contaminated water or mud at that location will attract bees, and they will die. Bees are water gatherers before they are pollen gatherers. If the bees that collect water die, the hive is stressed, and pollen gatherers will revert to water gatherers. This will diminish the colony’s effectiveness for pollinating tree fruit.
I am often asked if dandelions should be killed or mowed to prevent bees from spending time on the weeds rather than the fruit blossoms. Dandelions are extremely beneficial in the orchard and will actually assist in pollination. Dandelions are a good source of nectar. Only the last two weeks of a bee’s life is spent as a nectar gatherer. During this time, the bee will search for nectar wherever she can find it. If there is little nectar in the orchard, the nectar gatherers will leave the orchard in search of nectar. If dandelions are present, the nectar gatherers will fly throughout the orchard collecting nectar from the dandelions.
Once a bee is loaded with nectar, she is too heavy to fly directly to the hive. She will hop from blossom to blossom in her return to the hive. While doing so, pollen will stick to her legs and be transferred to other blossoms, providing pollination. Pollen-gathering bees will prefer the pollen-rich blossoms on the trees over the dandelions. If a beehive has water, nectar, and pollen, it will thrive. If any of these elements are missing, the hive will not be as productive. What is good for the bee is good for the grower.
The amount of time needed to pollinate is dependent on weather. In very marginal weather, there are fewer bee flight hours, but the pollination window is longer because the pollen stays viable for longer. Blossoms open in a more staggered sequence. During very hot weather, the blossoms open more quickly, and the pollen stays viable for a very short time. Both extremes require more bees present in the orchard.
Temperature will affect the length and timing of the bloom, as well as the hours of bee flight and the number of bees flying. Unfortunately, Mother Nature is beyond our control. The key to successful pollination is having the proper components in place to insure a crop in spite of weather conditions.