Which Garden Vegetables and Fruits Need Insect Pollination

Ruth O’Neill, Research Associate
Wanner Crop Entomology Lab, Plant Sciences & Plant Pathology

Knowing which plants require pollination can help you monitor bee abundance as well as seed and fruit set in your garden, and also help you improve the diversity of your gardens to benefit bees and other pollinators.

Honey bees and other pollinators are needed by many common urban garden plants to set seed and to produce edible plant parts, but not all of them.  For example, pumpkin vines and raspberry bushes will be completely barren if they are not visited by pollinators, while green beans and snap peas require no pollination at all.  Some plants need insect-pollination only for seed yield but not for production of the edible portion of the plant, so if the gardener is purchasing seeds each year then pollination is not needed.  Other plants are pollinated by the wind, or by self-pollination.  Some plants don’t require pollination at all.

Pollination is fertilization via the transfer of pollen from an anther to a stigma of a flower.  Self-pollination takes place within the same flower, or sometimes between genetically identical flowers on the same plant.  Cross-pollination occurs between plants.  Both self- and cross-pollination can be accomplished by bees, but bees are most commonly associated with cross-pollination.

Listed below are some common and not-so-common garden and orchard plants grown in Montana, with information on whether insects are needed for garden productivity.  

Case 1:  Insects Needed to cross pollinate for production of edible portion of plant.  
Pollination of these crops is mostly accomplished by bees, including bumble bees, solitary bees, and honey bees.  Flies, butterflies, and other pollinators may contribute as well.  In some of these crops, such as faba bean, a low percentage of successful self-pollination can also occur though cross-pollination is more common. 

Case 2:  Buzz-pollination of self-fertile flowers by bees needed for production of edible portion of plant.  For good fruit set, some garden plants strongly benefit from (or even require) bee visitation even though the flowers are self-fertile.  Pollen in these plants is held in hollow anthers with pores at the tip, like little salt shakers.  Vibration releases copious pollen, some of which lands on the female parts of the same flowers.  This is accomplished via “buzz pollination”, in which bees deliberately vibrate their wing muscles, creating a high-frequency vibration on the flower.  Only bumble bees and solitary bees perform the buzz-pollinating behavior – not honey bees. In the absence of bees, gardeners can buzz flowers by hand with an electric toothbrush applied to the back of the flower for about one second.

Case 3:  Insect-facilitated pollination needed to produce non-edible seed.  These garden plants do not require cross-pollination to produce a harvest.  However, for gardeners interested in raising and saving their own seed, bee pollination is needed.  Please note that some of these crops are biennial and will not produce seed until the second year.  And some of these biennials will not overwinter in the ground in Montana, and so will need to be moved indoors during the cold months and re-planted in the spring.

 
NOTE: Raising garlic for true sexually-reproduced seed (i.e., not just the divided bulbs or the bulbils) is an art.  See Meredith and Drucker’s “Growing Garlic from True Seed” http://garlicseed.blogspot.com/p/growing-garlic-from-true-seed.html

Case 4:  No insect pollinators needed. 

These plants either self-pollinate to produce seeds and edible plant portions, or they are wind-pollinated.  Most types of beans have flowers that are self-pollinating, with most fertilization occurring before the flowers are even open.