How does this pollination stuff work anyway?
The nursery trade contains a lot of conflicting information regarding plant pollination. Credible sources contradict each other and it can leave your head spinning. One catalog will tell you that a certain tree is self-pollinating, another will tell you that you need to plant at least two. We feel that this is a reflection of a simple concept: nature doesn’t walk a straight line. Some technically self-fertile plants don’t do so well setting fruit alone; other supposedly self-infertile plants set fruit heavily even when they are apparently isolated from their buddies. Then you add soil types, weather, cultural practices…oh my. Isn’t it good to be reminded of how little we really understand about nature?
Our catalog notes about pollination requirements for each plant are primarily based on our own observations and info we’ve gleaned from the experts. When there is any doubt, we suggest multiple plantings to ensure fruit sets. Here are a few definitions to help shed light on some commonly used botanical terms
Self-pollinating, self-fertile and self-fruitful all mean the same thing. You can plant a self-fertile tree and expect it to pollinate itself and set fruit alone (for example, peaches, pie cherries, apricots). However, many self-fertile trees’ fruit sets are enhanced with multiple plantings (elderberries and amelanchiers).
Self-sterile or self-infertile means that another tree of a different cultivar or variety is needed to set fruit (cross-pollinate). This is the case with most apples.
Monoecious (from Greek meaning ‘one household’) plants have their female and male parts on separate flowers both together on the same plant. In most cases, these plants are self-fertile, but not always! (Black walnuts are monoecious but the male flower releases pollen before the female flowers open, so having two plants is better than one).
Dioecious (meaning ‘two households’) plants have either all male or all female flowers on separate individuals. You would need to plant one female and one male to achieve pollination. When you buy unsexed seedlings, you generally have a 50-50 chance of getting one gender or the other (ginkgo, spicebush, bayberry, sea buckthorn).
Bisexual or Perfect flowers contain both male and female components within the same flower. Some plants with perfect flowers will be self-fertile, some will not. Often, specific cultivars or varieties have perfect flowers but they cannot pollinate themselves and need other varieties to assist them (apples and blueberries).
Pollen Nation - Supporting Pollinators
We owe thanks to our pollinators for giving us food to eat and seeds to grow. Bees, birds, bats, moths, flies and butterflies gather protein-rich pollen and sugary nectar from flower to flower while cross-pollinating our food crops and almost every plant we see (except of course those dependent on wind pollination.)
Yet many of our pollinator species are threatened, endangered or extinct from widespread chemical use on farms and gardens, genetically modified crops, and loss of habitat due to development. Bees are considered a “keystone” species, meaning that many other species depend on them for survival. Their extinction means our extinction. So why do we continue to harm them while at the same time demanding so much?
We can begin to help our pollinators by incorporating native plants back into our landscape and creating forage in places where it’s lacking. We can make our gardens a natural habitat for insects rather than a toxic place that only exists for our enjoyment. It’s a critical time to create gardens that mimic the native environment and help our suburbias (and farms!) be a little more natural. Below, we highlight some ways to encourage pollinators to come onto the scene and some of the plants that attract them.
Over millions of years, plants and pollinating insects have evolved together. Certain pollinators favor certain flowers depending on which colors they can see or which shapes their mouthparts fit into. Below we’ve outlined some patterns, but bear in mind it’s only a rough guide—pollinators are not always picky and tend to jump around. Every visit to the garden is an opportunity to observe pollinator habits.
Nectar-rich flowers attract butterflies, which typically don’t gather pollen, but extract nectar with long proboscises.
Abelia (Abelia mosanensis)
Butterfly Weed (Asclepias spp.)
Butterfly Bush (Buddleia spp.)
New Jersey Tea (Ceanothus americanus)
Echinacea (Echinacea spp.)
Joe Pye Weed (Eupatoreum spp.)
Blazing Star (Liatris spp.)
Mexican Sunflower (Tithonia rotundifolia)
The nectar of red tubular (trumpet-shaped) flowers attract hummingbirds, which see red and have long narrow beaks that fit perfectly into deep flowers.
Red Buckeye (Aesculus pavia)
Wild Columbine (Aquilegia canadensis)
Flowering quince (Chaenomeles spp.)
Cardinal Flower (Lobelia cardinalis)
Bee Balm (Monarda spp.)
Weigela (Weigela florida)
Umbelliferous (umbrella-shaped) flowers attract beneficial insects such as parasitic wasps and syrphid flies that have small mouthparts that fit perfectly in the tiny little flowers. Not only are these insects good pollinators but also the best ecological pest management around!
Yarrow (Achillea millefolium)
Dill (Anethum graveolens)
Angelica (Angelica archangelica)
Lovage (Levisticum officinale)
Sweet Cicely (Myrrhis odorata)
Parsley (Petroselinum crispum)
Elderberry (Sambucus spp.)
Viburnums (Viburnum spp.)
Purple and blue flowers are often pollinated by bees, which see the ultraviolet end of the spectrum.
Monkshood (Aconitum carmichaelli)
Blue False Indigo (Baptisia australis)
Echinacea (Echinacea spp.)
Hyssop (Hyssopus officinalis)
Lavender (Lavandula spp.)
Catmint (Nepeta faasenii)
Russian Sage (Perovskia atriplicifolia)
Baikal Skullcap (Scutellaria baicalensis)
Composite (daisy-shaped) flowers attract many kinds of bees and also provide a sheltered sleeping place for male bumblebees, which don’t return to the nest. At dusk or early morning they can be found tucked under the petals, sleeping soundly upside down.
Arnica (Arnica chamissonis)
Calendula (Calendula officinale)
Echinacea (Echinacea spp.)
Gaillardia (Gaillardia spp.)
Sunflower (Helianthus annuus)
Rudbeckia (Rudbeckia spp.)
Host Plants for Butterfly and Moth Larvae
We often talk about nectar sources for butterflies and moths, but what about plants that feed their larvae? Certain host plants are required for the reproduction of this group of insects, the genus Lepidoptera. Host plants are always native because they have evolved over thousands of years with the dependent insects. While butterflies love the nectar of non-native Buddleia, they will never lay eggs on that plant because it is inedible to their larvae. Here are some important woody host plants and trees to incorporate into your landscape:
Maple (Acer spp.)
Birch (Betula spp.)
Hickory (Carya spp.)
Chestnut (Castanea spp.)
Hawthorn (Crataegus spp.)
Dogwood (Cornus spp.)
Hazelnut (Corylus spp.)
Spicebush (Lindera benzoin)
Native Crabapple (Malus coronarius)
Eastern White Pine (Pinus strobus)
American Plum (Prunus americana)
Oak (Quercus spp.)
Black Locust (Robinia pseudoacacia)
Willow (Salix spp.)
Linden (Tilia americana)
Elm (Ulmus americana)
Blueberry (Vaccinium spp.)
Viburnum (Viburnum spp.)
Native Pollinators for the Orchard
Each year it seems harder and harder to overwinter honeybee hives. While honeybees are not native to North America, they sure do a good job pollinating our agricultural food crops. It’s hard to imagine a world without honey! Though we love them dearly, we must point out that it takes 10,000 or more honeybees to do the same amount of pollinating as only 250 native mason bees! Natives fly earlier and later in the day than honeybees and through wetter and colder conditions. Also, they are more successful pollinators because they carry pollen all over their bellies instead of in “pollen baskets” on their hind legs.
Most native bees are solitary dwellers, unlike the social honeybee. They have single nests in holes in wood or in the ground. Two of the best species for pollinating tree fruits are the blue orchard mason bee and the leafcutter bee. One way to encourage native bees is by growing plants that provide early-season forage, like willows, dogwoods, amelanchiers and viburnums. You can also invite bees to the garden or orchard by building simple nest boxes.
Building a wooden block nest box for solitary native bees
Of course native bees can find their own nesting spots, but it’s easy to help them by drilling horizontal holes into fence posts or by making wooden block nest boxes.
Grab a random piece of untreated wood, 4x6'' or so and at least 6'' deep. Drill several holes of different sizes. Smaller bees nest in 3/32–1/4" diameter holes, 3–5'' deep; larger bees need 1/4–3/8'' diameter holes, 5–6'' deep. Holes should be drilled 3/4'' apart and this same distance from the edges. Choose your length. Bees will not nest in holes that have both ends open, so tack a board on the back if holes punch through. They do not like rough holes so make the sides of the holes smooth by using a sharp bit. If you really want to get fancy, you can throw a roof on to help keep off the rain. Mount block nest on a post or attach to a tree trunk near the orchard or garden. Discard nest boxes every few years so they don’t build up with parasites or diseases.
Ready-made nest boxes are available here.