Paths of Pollen

Who would think that a collection of essays on pollen that ends with 23 pages of citations of scientific studies would make fascinating reading for non-scientists? Paths of Pollen wins the prize.

Stephen Humphrey writes of varieties of pollen, of pollinators, of strategies for pollinating, and of many challenges to the process. If you thought honey bees did all the world’s pollinating, he introduces you to the many alternatives – dozens of other kinds of bees, other insects like beetles, animals like bats, even the wind. A few plants even pollinate themselves.

Pollen is tough. Microfossils of pollen survived the Permian Extinction 250 million years ago. Now these fossils have become evidence of the existence of extinct trees otherwise unknown.

Colony collapse, the loss of vast numbers of honeybee hives, made headlines in 2006. Humphrey presents a study suggesting that collapse may not be the most serious problem. Although the cause of collapse remains a mystery, plenty of honey bees survive. Wild bees, on the other hand, face more dire problems.

Squash bees visit and pollinate only flowers of the squash family, including pumpkins, as well as many kinds of squash. These bees live underground, in tunnels they dig themselves. A bee weighing a tenth of a gram displaces three grams of dirt in the process, thirty times its weight. The species has adapted over several thousand years of connecting with squash agriculture, notably Native American agriculture, but elsewhere as well. Now it may disappear. Pesticide used to prevent wilt is widely sprayed on the ground, where the tunnels are, endangering these bees. If honey bees do become scarce, wild bees will be essential.

Numerous accounts like that of the squash bee make this book a good read. Particularly of interest to gardeners, it resonates for all of us who recognize the value of plants.

Reviewed by Priscilla Grundy in The Leaflet, Volume 12, Issue 3, March 2025.

Growing kiwi

I have two very healthy kiwi vines, one male and one female. My female plant is flowering profusely right now, but there are no flowers on the male plant. I have had the plants for about 15 years or more and have never had fruit. They do not seem to bloom at the same time. I have just never bothered about it before, but this year I thought I would check out some options.

Any resources regarding hand pollination (both instructions and local suppliers) would be really helpful.

Oregon State University Extension’s guide, Growing Kiwifruit by Bernadine Strik (2005), has information about pollination:

“For fruit to be produced, male and female vines must be present in a block and must flower at the same time. Male flowers produce viable pollen for only the first 2 to 3 days after opening. However, female flowers are receptive to pollen for 7 to 9 days after opening, even when the petals have started falling.

“Pollination is extremely important in kiwifruit production. Large fruit contain 1,000 to 1,400 seeds (research on Hayward). If pollination is poor, fruit will have indentations (narrow valleys) on one side or be non-uniform in shape. If you cut through these fruit, you will find no seeds in these areas.

“Kiwifruit flowers are pollinated mainly by insects, although wind may play a minor role. Honey bees are the main pollinator used in kiwifruit vineyards. Kiwifruit flowers do not produce nectar and are relatively unattractive to bees. About three to four hives per acre are needed to adequately pollinate kiwifruit. Place these in the vineyard no sooner than 10 percent bloom of the female vines.

“In some years, you may have no male vines in flower as a result of winter injury to male plants (they are less hardy than the females). In this case, no naturally produced pollen will be available. To get a crop, the females will have to be pollinated artificially. Call your county Extension agent for more information on sources of pollen and methods of artificial pollination.”

(Note the section on Hardy Kiwi which are different than Fuzzy Kiwi.)

You might also find this article from The Olympian newspaper (May 16, 2009) of interest. It features kiwi growers Hildegard Hendrickson and ‘KiwiBob’ Glanzman, and discusses hand pollination, general care, pruning and training.

Actinidia, Pollination

attracting pollinating insects

What flowering plants should I place near my two blueberry plants in containers on my driveway that might attract the kinds of insects to maximize pollination of the blueberry plants?

Almost any plant that flowers at the same time your blueberry plants flower will help attract pollinating insects. This could be anything from apples to clematis to more blueberries. The Xerces Society (a Portland-based conservation organization) has published this useful fact sheet about choosing plants to help our native bees.

on monoecious plants and bisexual flowers

My neighbor says his Deodar cedar tree is bisexual, and it’s the male cones that are making so much pollen this October. He seemed to be saying this was unusual, and that not all cedar trees were like this, with both male and female cones. What’s the story?

Cedrus deodara is monoecious, which means that an individual tree will bear separate and unisexual male and female flowers. If the tree had bisexual flowers, each flower would be ‘complete’ and ‘perfect,’ that is, with male stamens and female pistil in each flower. So it’s clearer to call the tree monoecious than to say it is bisexual. According to Wayne’s Word: An Online Textbook of Natural History, “about 90 percent of all flowering plants have bisexual flowers with both male (stamen) and female (pistil) sex organs. The remaining 10 percent have unisexual male and female flowers on the same plant (monoecious species) or male and female flowers on separate plants (dioecious species).”

Most conifers (like true cedar) are monoecious. The male pollen cones are 2 to 3 inches long by October, and are found in great number on the lower parts of the tree. Female flowers are tiny, and usually found high up in the tree. Female seed cones take two years to mature. You might wonder how pollination can take place if the female flowers are up high and the pollen is down low. Conifer pollen is wind-dispersed, so it might seem arduous for it to reach the female flowers up above. However, if you consider the geographic origins of the true cedars, you will notice that Deodar cedar is also called Himalayan cedar and like the cedar of Lebanon (C. libani) and the Atlas cedar (C. atlantica), its native range is mountainous. Imagine cedars growing on a sloping mountainside, and you can easily picture the pollen drifting downward to female flowers on the trees below.

grape vine producing uneven fruit sets

What causes some grapes to get to normal size and others to stay small? This is on a Concord vine about 7-8 years old.

Some varieties of grape produce naturally straggly clusters of fruit. According to The Grape Grower: A Guide to Organic Viticulture by Lon Rombough (Chelsea Green, 2002), Concord has a tendency to ripen unevenly in hot climates (such as the mid-South), but he doesn’t note straggly clusters as a characteristic of this variety. That makes me think the uneven size of your fruit is more to do with pollination. See the following, from Oregon State University Extension, which suggests that a cool, wet spell around the time of bloom can interfere with pollination and result in large numbers of unset berries. Rain, which also inhibits pollination, can also be a factor in poor fruit set.

There are other possible reasons for the uneven fruit set. If you are growing a variety of grape which is not ideally suited to your climate, or if the soil is overly rich or overly fertilized, you may not get abundant fruit.

Our Native Bees

[Our Native Bees] cover

Paige Embry is an engaging and humorous writer exploring the topic of bees. And not just any bees. She is passionate about “Our Native Bees”, which is also the title of her new book. She gives honey bees their due, but laments they “get all the press – the books, the movie deals – and they aren’t even from around here.”

While I haven’t seen many movies on honey bees, the author makes her point. We have native bees that are far better pollinators, do equal work with fewer numbers, fly in nastier weather, and often use better technique. An example of the latter is buzz pollination, or shaking the pollen from the flower. Honey bees haven’t learned this trick, but bumble bees and others have and their work facilitates some of our favorite foods, including tomatoes.

This is not a field guide. While the author lives in Seattle, her scope for natives includes most of North America. There are some excellent, close-up photographs, but their purpose is to supplement the text, not help with ID. Instead, this is an investigative study of many apian topics and to recognize that bees are diverse and have the power to fascinate people, even when we mislabel or misunderstand them.

One of the author’s major themes is agriculture. For example, she studies the production of lowbush blueberries in Maine and neighboring New Brunswick, an interwoven history of wild plants, wild bees, managed plants, managed bees, and the impact of various attempts at pest management. Recounting this could be deadly dull, but in Emery’s hands, it is most engaging.

Throughout all the stories, there are questions asking what is possible. Can native bees provide better solutions for our pollinating needs? Can we provide better solutions for the needs of native bees? The author provides some answers to these questions, but I think her underlying goal is that we join her on a journey to a better understanding and appreciation of the diversity of bees, especially native bees.

Excerpted from the Spring 2018 Arboretum Bulletin.