May 18 2011

A simple explanation of tomato pollination, please?

Most plants in the wild are self sterile, ie. Nature dislikes incestuous propagation and prefers cross pollination, where the pollen is transferred between two genetically different plants. Cross pollination is achieved for most vegetables by an agent (called a pollinator), that physically moves the pollen. Usually this is a bee, because they are specially equipped to efficiently carry pollen; they are brawny, fuzzy, and have a static charge, so they acquire and transfer many grains of pollen.

In the case of the tomato, mankind has (perhaps unwittingly) selected plants with the defect of being self fertile. This likely came about as the plant was moved from its native area to other parts of the world without moving the native pollinators that were best equipped to cross pollinate them. So the surviving strains were the ones that had this defect.

Looking at cross pollination from the point of view of the fruit grower is utterly different from the point of view of the seed grower. With most plants, good cross pollination is very much desired, in some cases to make fruit at all, and in other cases to cause better quality fruit. Of course uncontrolled cross pollination makes the seed grower nuts, as he cannot predict exactly the characteristics of the plants grown from the seed.

Tomatoes are kind of a dream plant that can function both for the fruit grower and the seed producer. The reason is that they exhibit little “inbreeding depression.” That is, most plants, if they have any self fertility at all, will grow puny fruit and poor quality seed.

Tomatoes can be self fertilized and still be fairly vigorous.

In a discussion like this, someone always pipes up with the claim that tomatoes are “self pollinating.” This is a myth. Remember that myths are half truths. Most of the time, when you hear the myth, it is, of course, in the context of why tomatoes AREN’T self pollinating. Odd, isn’t it?

Most flowers have anthers (the male organ) that have the pollen on the outside. Anything that brushes the anther is likely to pick up some pollen. Tomato anthers are different; they are hollow tubes with the pollen grains inside. They are not released to the touch. The tomato must have help. It requires MOTION to release the pollen. Wind can accomplish this to some extent. Pollen grains are shaken loose and may land on the sticky stigma, thus accomplishing fertilization of some of the seeds.

Note that this is not self pollination, as the tomato could not do this of itself.

You can hand pollinate tomatoes by using any means of shaking the blossoms that doesn’t break plant parts. You can tap on the stem below the flower cluster with a pencil. Or you can hold an electric toothbrush against the stem. But the best tomato pollinator is a bee that “sonicates” or “buzz pollinates” the flower.

Sonication (Buzz pollination)

Bumblebee on a tomato blossom

Bees, most often bumblebees in eastern USA, will land on the flower, pulling it down until the anther is vertical (thus getting gravity’s help) and then vibrating their wing muscles (and their entire bodies) to shake loose the pollen. The vibration causes the flower to resonate, and many grains of pollen are shaken loose. This drops onto the bee’s belly, which is also vibrating. Some of it will stick to the bee and be available for cross pollination when she visits a flower on another plant.

Much of it will bounce right back up to the sticky stigma.

The development of the fleshy part of the fruit is stimulated by the fertilization of the seeds. Pollen grains on the stigma grow pollen tubes to the incipient seeds and fertilize them. If only a few grains of pollen are delivered, a fruit may form, but will not size up.

When enough grains of pollen are delivered to fertilize most of the incipient seeds, the fruit will be all that it can be.

If you are growing tomatoes for fruit, and not for seed saving, cross pollination is not of much concern to you. You just want good pollination to get the most and best fruit possible.

If you are growing tomatoes for seed, then you want to control the pollination more carefully. Generally, a gardener who saves seeds would want to keep an open pollinated variety pure, so you seek means to isolate the plants. This can be done by excluding bees (cages around plant or flowers), by sufficient distance between plants, or by timing bloom at different times.

Some tomato varieties are even nicer to the seed grower. The pollen is viable, even before the flower opens. If the flower gets sufficient motion (one reason why gardeners intuitively love early morning thunderstorms), it’s possible for the seeds to be fully fertilized quickly and keeping cross pollination down to a bare minimum.

May 18 2011

Turning our place into a bee sanctuary has paid off big-time!

No blossom drop!

Every flower in the cluster set fruit.

In many years, I’ve not seen tomatoes set every blossom, as they have this year. There are few of the blossom clusters with a “hole” where there is no tomato forming.

I’ve been exulting each morning as I watch the bumblebees “buzzing” the flowers. As they taper off, and go to other flowers, they are replaced by little flying emeralds – the tiny, in-your-face green bees that happily gather the remnants the bumblebee left.

Not everyone is aware of the debt we owe to the bees. Pollination can be the limiting factor for many crops, including tomatoes. I have had years when I added compost, adjusted the pH with lime, fertilized, and carefully weeded the plants I set out, only to see many of the blossoms drop off, and the total crop wind up a sorry one.

Tomato flowers do not give the bees nectar, only pollen, but this pollen is gathered by the bees for the nutrition of their young. As they do so, they make a trade with the tomato plants by aiding the fertilization of the seeds that will make next year’s crop.

In another blog post, I’ll discuss the mechanisms of pollen release, which is different for tomatoes than most crops, as well as discuss the popular myth of “self pollinating” tomatoes.

But for now, I just simply want to rejoice and enjoy the fruits of the labors of my little friends.

Feb 16 2011

Some Youtube treasures

It’s my intention to do a lot more video in the future, because more can be shown than is possible in still photos. Video is very difficult, espectially of fast-moving and spooky insects in the act of pollinating flowers.

Meanwhile, from time to time, I discover some very well done videos online. One needs to be careful of online resouces. Some are quite amateurish or worse, give innacurate information. Here are some that I find are good enough to recommend to this blog’s readers:

1.  Bee Pollinators of Southwest Virginia Crops:
There is sheer beauty in this video of honeybees, bumblebee queens & workers, bumblebee and halictid bee buzz pollination, orchard mason bees, digger bees, mining bees, longhorned bees, small and large carpenter bees, and squash bees mating.

There’s even a bumblebee “giving the tarsi” (the possible insect equivalent of “giving the finger”). One can watch this several times, and see new things in each viewing. This is also an excellent way to begin learning to identify common groups of bees. 
By Virginia Tech Entomology Department

2. Pollination Methods: Cucurbits:
This video starts off somewhat slow, but don’t get bored by the lengthy description of the various cucurbit species. It morphs into a good illustration of one means of hand pollination – a technique that may be quite valuable for gardeners who lack bees. Then it shows how hybrids are created, and shows the modern technology of “seedless” triploid hybrids.  Finally it ends with a clip on how to save cucumber seeds.
By the University of Wisconsin, Madison

 3. Honeybee collecting pollen:  Few people realize that honeybees make an active choice when visiting flowers. This may be based on the resources of the flowers, or, more likely, on the needs of the hives.

To collect nectar, or to collect pollen is the choice. Worker bees that are collecting nectar take longer in each flower, probing the flower’s nectiaries with their tongues for sweet droplets which they carry in their crops back to the hives. Bee that are gathering nectar will accomplish some pollination by accident. 

But other bees make the choice to deliberately gather pollen, likely because there is quite a bit of open brood in the hive that requires the pollen for protein for its development. This is the subject of this shore clip.

These bees do not probe with their tongues; rather they “doggy paddle” through the stamens to get as much pollen as possible to adhere to their fuzzy bodies. Then they comb this polle into their pollen baskets and carry it home.
Bees that are deliberately gathering pollen are as much as ten times more efficient pollinators than those who are gathering nectar.

Beekeeper who provide pollination service try to manage the hives so that they maximize open brood at the time of the crop’s bloom. This provides incentive for the worker bees to gather pollen, and makes them more efficient for the farmers’ needs.

I am always looking for more good videos, so if you have an especially good site to recommend, please do!

Feb 6 2011

Gardening for the bees in the Southeast: Part II

With no effort on our part, we are already blessed with some feed for the bees, especially in the spring, either on our property or nearby.  To these we have also been adding plants as we could.  We want to help fill in the major gap that occurs during hot weather.

Here are some of the plants that help take care of our bees, along with our thoughts on their value:


Dandelion, henbit and charlock in nearby fields will bloom throughout winter except in the coldest spells. In the dead of winter, I usually see only honeybees working these, but toward spring, other species join them. (No we do not herbicide our lawn “weeds,” as these are important forage plants – and we don’t want to contaminate our ground water. Plus their blossoms are pretty in their own right!)  All three of these plants are introductions, but so far as we know, there are no native plants that fulfil the same function


Red maple trees bloom nearby in February, and willow trees soon after. Both provide forage (food) for honeybees. Tupelo adds a major nectar source in April. There are a few flowering quinces in the neighborhood; bees love these. Crocus and daffidils also get bee attention.

Redbud trees also bloom early, usually by the end of March. Carpenter bees and honeybees tackle redbuds furiously. Chickasaw plum and some domestic plums in the neighborhood are the first of the fruit blossoms that supply lots of nectar. Dogwood is NOT a significant bee plant; bees rarely visit their blossoms.

Oaks, pecans, hickories and pines shed a lot of pollen, which bees sometimes gather, but it is of low nutritional value. An occasional black locust is highly favored by the bees, as is Carolina cherry.

Dewberry is a major pollen source in March and early April, followed closely by blackberry which gives both pollen and nectar. Apples, crabapples, and pears usually feed the first queen bumblebees, though I have occasionally seen queens on plums earlier. Apples are very important for orchard mason bees, carpenter bees and honeybees. We have planted low-chill apple varieties which are suited to the South.

Wisteria and azaleas explode with blooms in April and are important feed for bumblebees. The first tiny Lasioglossom bees are often found on the stamens of azalea blossoms.

Carolina jessamine yields toxic nectar that kills honeybee brood. Photina (red tip) is a good feeder, if it is not trimmed for hedges.

Dahoon holly and boxwood are practically attacked by a variety of bee species. A few years ago, bradford pears were likewise covered with thousands of andrena bees when they bloomed. Today these bees are very scarce; you’d be lucky to see a half dozen on a tree, along with a couple honeybees and a bumblebee or two.

By the end of April, spiderwort is worked by a variety of bee species, especially Lasioglossum. Plantain also begins to feed Lasioglossum bees. A variety of blueberry and huckleberry species bloom from early April to early June, giving the blueberry bees good forage. Carpenter bees love these as well, but do not pollinate them, as they cut slits at the base of the petals to steal the nectar. Carpenter bees will also do this for honeysuckle, buckeye, and other flowers with a deep corolla.

Megachilid bee on privit

Privit is regarded as invasive, but this megachilid bee doesn't care. Privits that are kept trimmed for hedges do not bloom, but when they go wild, become small trees which provide excellent bee forage.

By late spring we have more garden flowers, including vegetables like squash, cucumbers, tomatoes, peppers, eggplant, butter beans, and okra. Marigolds do feed a few bees, but do not seem to be of major interest. Likewise zinnia seems to be of some small use. Cosmos has been a major hit with the bees. Bee balm is significant, but only blooms for a short time. Its wild relative, horsemint is much better for bees. Cultivated morning glories are a big bust, as bees show little interest, though their wild (and highly invasive) relatives are much more attended, by bumblebees and megachilids.

Passion flowers are very good, and clematis attracts a few bumblebees. Lantana and butterfly bush seem to only be important to butterflies. Lasioglossum seems to love parsley blooms.

Sunflowers are a major hit with melissodes bees and honeybees. We plan to plant more of these – our only complaint being the relatively short bloom period for each planting.

A halictid bee on sunflower blossom

A halictid bee loads up on sunflower pollen.


When the hot weather of summer comes, there is a dearth of flowers. A few trumpet vines help feed bumblebees. An invasive plant, Brazillian vervain, supplies nectar through the hottest periods. Bitterweed begins to bloom in the heat, and is heavily worked by megachilid bees. Butterfly weed is present in sparse amounts; we aim to increase the supply of this. There are also occasional pine hibiscuses, which bees seem to love.

Sumac is also present around in spotty amounts – the southern variety blooming in midsummer, unlike in the north, where it is a spring flower. Sometimes sumac will be literally covered with bees. too bad it’s not a common plant.

Caryopteris – a plant we brought from Tennessee – gets wild applause from the bumblebees.

Another hot weather plant is crape myrtle, which does get a steady, though small amount of attention from bees.  Once cotton begins to bloom, honeybees and bumblebees will concentrate there, and of course, they frequently get poisoned.


By late August, we begin to see more fall flowers which bloom in a progression through the end of November. Joe Pye weed is wonderful for the bees, as are any of the various goldenrod species. Many asters, such as mistflower, also bloom through the fall, with frostweed continuing after frost many years.

Rudbeckia and Bidens are extremely important wildflowers, through the fall, feeding a variety of bee species.

We’ve listed quite a number of forage plants on or near our home. We could list a lot more, within driving distance.  But many of them, though important, are quite sparse in occurance. Roadside mowing and herbicide use, hedgerow removal, pine plantations and the chemlawn mentality have removed many of the wild bee forage plants.

Flower gardens can help, but many of the showiest flowers are overbred and of little value to bees. We tore out our roses, when we found that the bees had no interest in them and they were prone to fungus diseases and needed lots of spraying to keep them pretty.

In another post, we’ll be talking about native vs alien plants, and some of our use of each. Your thoughts (on the topic) are always appreciated.

Dec 4 2010

New guide available on increasing native bee benefits

Native bee benefits:  How to increase native bee pollination on your farm

Written by:  Neal Williams, Bryn Mawr College, (610-526-5091,
and Rachael Winfree, Rutgers University (732-932-8315,

Can be downloaded from:

The pamphlet is a very informative one, with some really good photos as well, and I commend the authors on providing a good new resource for pollination management.

While I heartily endorse much of the pamphlet as very valuable, there are a couple misleading points,  and one glaring error that I’d like to point out as a critique. Perhaps the authors need to consider this for an update.

1. Much is made of colony collapse disorder in honeybees. This is similar to past unexplained die-offs that have occasionally occured in beekeeping history, only this one was at a larger scale. Much of this loss seems to have run its course, and the bees were easily and quickly replaced, except in cases of beekeeper bankruptcy. At any rate the beekeeping industry, with some research help, is on the way to solutions to CCD.

What is not made clear is that wild bees are not so quickly and easily replaced; thus are of much more concern. And with this, we go back to the biggest problem for all bees, which beekeepers have been trying to solve for a couple generations, and have been unable to get any significant help.

The problem is pesticide misuse – violation of the pesticide label directions – that continue to occur. In most cases wild bees and feral honeybees have no legal protection; lip service is given to protecting managed honeybees, but most “protection” involves advising pesticide users to evade the pesticide directions, by notification of beekeepers.

A pesticide user is the one who makes the choice to use a pesticide, and he is responsible for its safe use, yet these notification schemes allow him to dump the trouble and expense for protecting the bees onto others who are not benefited and have no way to recoup the costs.

Pesticide misuse is the greatest single danger to all bee species. Wild bee advocates and beekeepers need to be working together to get enforcement of label directions – which generally forbid applications in conditions where they are a threat to foraging bees. (And the labels only say “bees,” yet the pesticide cops tend to interpret this clear direction as only applying to honeybees.)

2. Several times the pamphlet mentions “attracting bees.” This is a flawed mindset. When populations are thin, bees can’t be attracted, or if they are attracted in small numbers, they tend to go to the rich food sources planted to attract them, rather than to the crops that need pollination.

What is needed is another mindset – pollination managers need to have an overall view that strives to restore stable normal populations of bees by giving them habitat, including nesting sites, continuous forage, and pesticide protection. The pamplet does explain this, but undoes it to a certain extent, by frequent reference to “attracting bees.” When pollinator populations return to normal, competition for forage will ensure that ALL blossoms get the required visitation.

3. Carpenter bees are NOT good blueberry pollinators. They are notorious nectar thieves with flowers with a deep corrolla, such as blueberries. Then they leave a slit in the side of the corrolla, enabling other bees to happily steal the nectar as well, without contacting the sexual organs of the flower.

Carpenter bees are excellent pollinators of fruits with open-faced flowers, such as blackberries, apples, plums, peaches; and of flowers designed for a large bee, such as passionflower.