Planting for Pollinators

The showy flowers of Asclepias curassavica, the tropical milkweed, and its compact growth habit have made it popular with gardeners and wholesale growers. This species is tender, so is replanted each year. The flowers draw butterflies and bees; the foliage can feed Monarch caterpillars.

Asclepias speciosa, Showy milkweed, is a California native with soft pink flowers and grey foliage, so the whole effect is subtle and elegant. It can get to about four feet all and is rather robust and perennial. Excellent addition to a drought-tolerant landscape. Photo courtesy of Nevin Smith, Suncrest Nurseries

Butterfly bushes are aptly named. These very popular garden shrubs have, until recently, been large and somewhat rangy things for the back of the border. New dwarf hybrids are now available that stay under five feet tall, and are also sterile so they don't reseed.

A recent morning's visitor, this pipevine swallowtail spent much of the morning visiting buddlieas, salvias, cosmos, and other flowers. A diversity of colorful blossoms over a long season keeps butterflies coming to your garden.

The origin of the common name of pipevines is obvious. This hybrid is readily available, but unfortunately is not fed upon by the native pipevine swallowtail. And the strange flowers are quite malodorous.

Passiflora blossoms are very showy, some are almost unearthly. This variety called Purple Tiger has a spicy fragrance and looks, as one boy put it, like a space alien jellyfish. Our native carpenter bees love the flowers.

Passion flower vines are vigorous and bloom abundantly. Some types act as food sources for the Gulf fritillary caterpillar (which means you will have to tolerate watching them eat your vine). All passionflowers attract various of our native bee species. This carpenter bee was so intoxicated that she stayed basically immobile for about three hours. Sugar high, I guess.

Closeup of this Salvia flower (variety: Dark Dancer) shows the unique pollination mechanism. A nectar reward at the base of the flower tube draws butterflies, bees, and hummingbirds. Inside the flower, following the curve of the petal, is an anther bearing pollen, which is deposits on the back of the unsuspecting bee. The part poking down from above is the stigma (female part) which receives the pollen that the bee picked up at the last flower.

Bees and monarchs in the news

I'm always happy to see stories about particular pollinator species in the news. Curious, perhaps, that the non-native European honeybee sparks so much concern, while the status of the 4,000 or so species of native bees gets very little attention.

But what's good for one pollinator can help others, and gardeners are taking an interest. So that's great. And there are lots of other types of pollinators, including butterflies and hummingbirds, that will happily visit your garden if you provide the right plants and conditions.

First principle is to have lots of different plants flowering over all seasons. A bunch of mixed perennial and annual flowers will be more effective than, say, a garden solely of rose bushes.

Second principle is to retain some dense, kind of overgrown areas, include some grass species, and have some open uncultivated soil to provide for the different stages of the life cycles of pollinator species.

What you want to provide is at least three or four types of plants blooming at all times, some nearby shrubs and larger plants where wildlife can rest, nest, and feed.

Grasses help to provide habitat and hiding places for beneficial insects. Soil that you leave undisturbed can provide nesting sites; many of our native pollinators live in burrows in the ground. This all can be very low water. Deep, infrequent soakings are best for most of the plants listed.

Here are some garden plants for pollinators, by season of bloom.

Many landscape shrubs have flowers that attract pollinators. Examples include native shrubs such as toyon (Heteromeles) and wild lilac (Ceanothus), as well as tough non-natives such as Xylosma, butterfly bush (Buddleia), and even the lowly privet. All will draw and sustain native bees, honeybees, and other pollinators into your landscape.

Food for butterflies?

The precipitous decline of the beautiful Monarch butterfly in its Mexico overwintering sites has received a great deal of media attention. Most media sources are attributing that sudden drop in population to loss of habitat and food sources in the midwest. The populations that overwinter in coastal California appear to be more stable, though at a low ebb.

Various publications and organizations are urging you to plant milkweed (Asclepias species), because that plant is the sole food source for Monarch caterpillars. Consequently, wholesale nurseries are selling out of Asclepias as fast as they can grow it. Good news: Asclepias is very, very easy to grow. Some types have very showy flowers which attract butterflies of various species in addition to the Monarch. You can easily grow milkweed to draw adult butteflies, but it may become a larval food source, which means that you will need to tolerate caterpillars eating your plants.

There are several dozen species of milkweed, all of which appear to be possible food sources, but only a handful are actually common in the trade. A few examples:

There is a common misperception from various online sources that native species of Asclepias are preferred as food sources. The issue is that the milkweed, which contains cardiac glycosides, renders the caterpillars poisonous and repellent to birds, which then avoid them.

So does a larval food source from a non-native species make the caterpillar more subject to predation? I asked our resident butterfly expert, Dr. Art Shapiro, who replied that Ònative species are neither necessary nor preferred. As it happens, curassavica is quite potent--more so than any of our common natives. Tropical and subtropical species are generally quite potent, as are species from desert environments and on harsh soils.Ó

There is a species of orange aphid that always seems to show up on milkweeds. It also just seems to disappear, prey to various beneficial insects and birds. So you can just leave it alone, or wash it off with water if it bothers you.

Some other plants to feed butterfly larvae.

There are two other plant/caterpillar relationships that gardeners may try to cultivate (pun intended). The caterpillar of the Gulf fritillary butterfly feeds on the foliage of some species of passionflower (Passiflora). Passifloras are vigorous vines that range in hardiness and degree of garden-invasiveness (ask!), and the occurrence of the caterpillars is pretty haphazard. But the blooms are incredible, some having a spicy scent, and they draw various native bees for pollination.

Pipevine swallowtail, a native butterfly species, is attracted to many different flowers for pollination. But its larvae exclusively feed on native pipevine (Aristolochia californica). The relationship is similar to the monarch butterfly: the pipevine contains toxins that make the caterpillar unpalatable to predators. Most nurseries grow hybrid pipevines, as they are easier to propagate and have showier flowers. But they won't act as food sources.

Another oddity about pollination: Aristolochia californica, like many other pipevine species, is pollinated by insects that feed on carrion. How does a flower draw carrion flies and gnats? By smelling like rotten meat. I have found this limits the sales appeal of this species. The last time we had one in stock, we spent a couple of days looking for the dead animal before we realized where the odor was coming from.

One of the great pleasures of my job is being greeted each morning by a panoply of interesting and unusual flowers, and watching the insects and birds that visit them. We provide a mix of blooming plants, simple water sources, and we manage pests naturally. Even in a limited space you can do the same, and watch bees, butterflies, and hummingbirds visit your garden daily, year-around.

Planting for Pollinators

Butterflies, bees, and more!

Bees and monarchs in the news

Here are some garden plants for pollinators, by season of bloom.

Food for butterflies?

Some other plants to feed butterfly larvae.