See Why Cross-Pollination Is a Plant’s Best Friend

Getting the most from a native plant landscape goes beyond plant selection. You often need compatible partners too

Curtis Adams April 22, 2017

Houzz Contributor. Landscape designer, native plant enthusiast and blogger located in west-central Maryland. I have always had an interest in things botanical, especially species that are native to a particular locale. When it was time to start a second career I decided that the best way to build on this interest and to educate others about the wonderful plants that grow in their own region was to train to become a landscape designer. I completed the Landscape Design certificate program at Harvard's Landscape Institute and launched my own business, Adams Garden, in the Boston area. In 2012 I moved to Knoxville, MD where I am continuing to evaluate native plants, work on removing invasive plants and continue my design business. You can find my blog at http://adamsgardennativeplants.blogspot.com/...

Houzz Contributor. Landscape designer, native plant enthusiast and blogger located... More

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You can provide more than just summertime nourishment for bees and butterflies in your garden with plants that produce berries, seeds and fruit that are loved by birds and other small animals in fall and winter. Getting plants to bear seeds and fruit requires that they be successfully pollinated. Some plants are able to self-pollinate, but more than half of the flowering plants have developed mechanisms that either encourage or require cross-pollination.

For some of the more commonly used landscape plants, like crabapples, hollies, junipers and yews, your neighbors may already have suitable partners for cross-pollination planted. For native species, there may be some wild-type plants in your area that are able to cross-pollinate your plants.

If you are not getting a good yield of seeds or fruit on a plant you already have and you would like to improve the situation, adding an appropriate “mate” may be all that is needed. What follows is a listing of some wildlife-friendly plants whose value can be enhanced with plants that provide cross-pollination.

Proven Winners

Viburnum dentatum ‘Christom’, sold as Blue Muffin, is noted for its sapphire-blue berries. You will get berries like these only if there is another compatible arrowwood viburnum close enough for cross-pollination.

Many of the plants that we purchase from the garden center or nursery for our home gardens are a single variety. We select them for their size, shape or color of bloom. Many of these are cultivars, or clones, that have been selected for their improved features, like color, bloom, size or shape. These cultivars reproduce these traits reliably because they are genetically identical. The downside of this is that many of these clones have a diminished capability to produce fully developed seeds and fruit because they are not able to cross-pollinate.

In addition to the following plants, there are many plant species that need cross-pollination to produce good quantities of seeds. If feeding the wildlife with homegrown seeds and fruit is an important part of your garden’s mission, then including more than one variety of each species, or using open-pollinated or wild-type plants, will help achieve that goal.

Paintbox Garden

This display of berries on winterberry holly requires that a male plant be nearby.

Male and female plants. There are a number of important wildlife-friendly landscape plants that ensure cross-fertilization by having separate male and female plants. These are referred to as dioecious plants. Unfortunately, except for hollies, it is hard to find information in the nursery on the gender of specific cultivars, and even harder for noncultivars.

When you can’t find out the gender of a particular wild-type plant, it is recommended to get at least three, if not five, individuals to increase the odds that you will get at least one of each sex. This works for seed-grown plants. For plants propagated by cuttings or grafts, all those new plants will be the same as the “parent.”

Here’s a partial list of some wildlife food plants that are dioecious.

White fringetree (Chionanthus virginicus): Male flowers are showier, but only female plants bear blue-black berries in late summer.
Persimmon (Diospyros virginiana): Large edible fruit appear in the fall on female plants only.
Hollies (Ilex spp.): All are dioecious except a few cultivars that bear both male and female flowers.
Junipers (Juniperus spp.): Sapphire-blue to black berries appear in late summer on female plants; males are not showy.
Spicebush (Lindera benzoin): Male flowers are somewhat showier in early spring; females have bright red berries.
Bayberry (Morella spp.): Neither flower is showy, but only females bear the waxy blue-gray fruit eaten by birds and used for candle making.
Black gum (Nyssa sylvatica): Both genders have nectar-rich flowers for bees, but females also have dark blue berries on reddish stems in the fall for the birds.
Sumacs (Rhus spp.): Greenish flowers appear on male trees in early summer; females produce tight clusters of reddish berries in late summer.
Willows (Salix spp.): Among the earliest-blooming shrubs, willows are a great source of pollen and nectar, and provide early-season seeds for songbirds.
Yews (Taxus spp.): Flowers are insignificant cones, but females bear bright red berries.

Note: Male pollen-producing plants, particularly trees, are known to trigger some people’s allergies.

Barbara Pintozzi

The beautiful red-flowered ‘Prairie Fire’ crabapple is an example of a cultivar requiring cross-pollination to bear fruit.

Apples and crabapples. Most varieties of apples and many crabapples need to be cross-pollinated to bear fruit. There are a few self-fertile varieties, such as ‘Fuji’ and ‘Golden Delicious’. But, in general, even the self-fertile ones produce higher yields of better-quality fruit if they are pollinated by a different variety or cultivar.

Other fruit trees that benefit from cross-fertilization are pears (except Bartlett), most plums and sweet cherries. Many nurseries specializing in fruit trees will have detailed information on fertility and bloom times.

Austin Ganim Landscape Design, LLC

The cultivars ‘Adams’ and ‘Donald Wyman’ are examples of self-fertile crabapples. They bloom at a similar time to ‘Prairie Fire’ and would be good partners to improve fruit production.

Bloom time is another consideration with apples. The two pollination partners need to be in bloom at the same time. Crabapples have a longer blooming period than regular apples and are often included in orchards to improve the availability of pollen.

Monrovia

Blueberries. This summertime favorite fruit comes from a number of North American species in the genus Vaccinium. Highbush blueberries (V. corymbosum) are found in the eastern half of North America and prefer moist environments. Another group of species is referred to as lowbush blueberries, typified by the wild blueberries of Maine. These include V. angustifolium and V. pallidum. These are shorter plants, often found in drier locations. There are also hybrids of high and lowbush blueberries, referred to as half-high blueberries. These combine the large fruit of highbush blueberries with the cold hardiness of lowbush species.

Although most of these blueberries will self-pollinate, fruit quality and quantity are much greater if you have at least two species that can cross-pollinate. While the blooming season of blueberries is fairly long, from early spring to early summer, a single variety may bloom for only a portion of that time. To help the gardeners, specific varieties have been grouped into early-, mid- and late-season blueberries. These times refer to harvest times, but that roughly correlates to bloom time as well.

When planting blueberries, you should get at least two cultivars with the same bloom time. Ideally, if you have space, you could get six varieties, two from each blooming group. For example, use ‘Spartan’ and ‘Patriot’ for early bloom, ‘Northland’ and ‘Bluecrop’ for midseason, and ‘Jersey’ and ‘Bluegold‘ for late season. With a large crop of blueberries coming, you can decide how much you get and how much you leave for the birds.

Pollination Press LLC

Here’s a bee handling the cross-pollination duties on the flowers of stiff goldenrod (Solidago rigida).

Composite, or aster, family. Most plants in the aster family (Asteraceae), which includes asters, coneflowers, coreopsis, daisies, goldenrods, sunflowers and zinnias, have some means to discourage self-pollination and encourage pollination by a separate individual of that species. Seeds from these plants are consumed by a number of bird species, such as goldfinches, chickadees and cardinals.

If you have only a single cultivar of one of these plants in the garden — for example, ‘October Skies’ aromatic aster or ‘Fireworks’ goldenrod — then seed production will be very low to nonexistent. Adding a second cultivar of the species or some seed-grown or wild-type plants of that species to your garden mix will allow for cross-pollination and an increase in seeds for your birds to dine on. (A side effect of all those seeds can be an increase in weeding to remove the new seedlings.)

Rustic Landscape Use your Landscape to Naturally Increase Food for Wildlife

In this area, I planted some native seedlings of purple coneflower and ‘Summer Sun’ smooth oxeye, a cultivar of Heliopsis helianthoides. The coneflower has since spread around the garden, while the smooth oxeye has remained in the three original clumps.

Dig Your Garden Landscape Design

When you look at how elaborate this vine’s flower is, it’s no surprise that it is designed for cross-pollination by insects — large bees, in particular.

Passionflowers. The exotic-looking passionflowers (Passiflora spp.) are a group of somewhat aggressive vines found in tropical areas around the world. There are nine species native to the warmer parts of the U.S. and a few more exotic species naturalized. Passionflower vines produce elaborate flowers in early summer, with fruit ripening in late summer and fall. Wildlife favor the fruit.

To get fruit, a flower needs to be pollinated by another genetically distinct passionflower. Since a single flower lasts only a day or two, it needs a ready supply of flowers from other plants blooming at the same time. If you have only a single plant or clone, you will not get any fruit.

Landscape Use your Landscape to Naturally Increase Food for Wildlife

The large leaves and unusual fruit of the pawpaw are more of what you would expect of its tropical relatives.

Pawpaw. The common pawpaw (Asimina triloba) is a southeastern North American native that is gaining in interest for its unusual fruit, which have a tropical, mango-banana flavor. To get fruit set, you need to have two genetically different pawpaw trees. Natural cross-pollination is done by beetles and carrion flies, which are not particularly good at traveling long distances.

You can improve fruit production by using an artist’s brush to transfer pollen from one plant to another. In pawpaws, the female parts (stigma) are receptive to pollen before the pollen of that same flower has ripened. In this way, self-pollination within the flower is avoided. Humans and small mammals consume the fruit, and the pawpaw is the larval host for the zebra swallowtail butterfly.

To get these multicolored berries, Viburnum nudum ‘Winterthur’ needs a partner for cross-pollination.

Viburnums. These are another example of self-infertile plants. These are often marketed for the beautiful berries that are produced in the fall; however, if you do not have a genetically different plant of the same species, berry production is greatly diminished.

As an example, ‘Winterthur’ smooth witherod (Viburnum nudum ‘Winterthur’) is noted for its blue and pink berries, but if that is the only cultivar in the area, no berries will be produced. By including a wild-type of V. nudum, or another cultivar like ‘Bulk’ (sold as Brandywine), in the area, production of the multicolored berry clusters is greatly increased. It should be noted that the ‘Bulk’ cultivar is self-fertile and can produce berries on its own.

The same holds true for southern arrowwood (V. dentatum). Here, planting two cultivars like ‘Christom’, noted for its deep blue berries, and ‘Synnestvedt’ or ‘KLMseventeen’ (sold as Little Joe) nearby will ensure a good berry yield.

Another exception is highbush cranberry, aka American cranberrybush, V. opulus var. americana (formerly V. trilobum). The species V. opulus is self-fertile and can produce large quantities of bright red berries on its own.

Well-Designed Interiors

These clones of ‘Bradford’ pear planted in matching rows create a formal allée. These will not bear fruit unless a different clone of the Callery pear (Pyrus calleryana) is nearby.

Some words of warning. In residential horticulture, optimizing fruit and seed production is not a major concern, and in some cases, it is considered undesirable. In fact, in landscapes and gardens that are strictly designed, and where maintenance costs are a major consideration, having more seeds and fruit would be negative factor.

From the ecological standpoint, you may not want to encourage fruit and seeds from exotics (by this, I mean plants not native to your region) unless they are known not to have invasive tendencies. The ‘Bradford’ pear (Pyrus calleryana ‘Bradford’) is an example of this. When there was only a single cultivar in use, it was effectively sterile. When new, improved cultivars of P. calleryana were introduced into the market, these were able to fertilize the original ‘Bradford’ that had already oversaturated the landscape, leading to the current invasion.

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