Garden Q&A – Insect-Friendly Gardens
CNPS Garden Q&A with Bob Allen
I’ve been reading about the insect apocalypse and declining monarch butterfly populations. Why are native insects important, and how can I support them in my garden?
Native plants serve as food and shelter for many species of native insects. Whether in the wild or in the garden, they exhibit a variety of fascinating interactions. We can boil them down to either one- or two-sided interactions.
One-sided interactions benefit the individual insects that feed on the plant, such as on sap, leaves, buds, and/or other parts. Since most herbivorous insects are host-specific — they feed only on one or a few related plant species — just having these native plants in the garden promotes survival of their dependent native insects.
- Larvae of the achemon sphinx moth, Eumorpha achemon, feed on leaves of native grapes, both Vitis girdiana and V. californica. Every year, the plants in my yard are inhabited by these caterpillars, which are surprisingly difficult to locate.
- When manzanitas (Arctostaphylos sp.), bloom in winter-spring, they are host to numerous species of native butterflies, flies, and bees, such as the red admiral butterfly (Vanessa atalanta). Every garden needs at least a handful of manzanitas.Two-sided or mutually beneficial interactions are activities that provide benefit to both insect and plant.
Certainly the most widely discussed two-way interaction is pollination.
As the insect gathers nectar and/or pollen, pollen sticks to its body, sometimes pow-dered all over like snow. Even the most careful insects inadvertently drop some of the pollen they so assiduously collect. Pollen that lands on a receptive stigma, either within the same plant/flower or between the flowers of different individual plants, successfully becomes an agent of pollination. Pollination, when successful, leads to fertilization, seed production, fruit growth, and seedling production.
If insects were 100 percent successful at gathering and retaining the pollen they encounter, there would be no polli-nation and therefore no reproduction of insect-pollinated plants. As Charles R. Darwin said, “Natural selection will not produce absolute perfection.” (On the Origin of Species, Chapter VI.) Fortunately for plants, he was correct; pollinating insects are sloppy.
A garden full of locally native plants provides food and shelter for native insects.
Adult insects use the pollen and nectar they collect to feed themselves and/or feed their young. Thus, pollen-collecting and successful pollination are both mutually beneficial interactions. Insect-pollinated native plants require insects for their own reproduction.
How can I support native insects in my garden?
We can support these native insects by using locally native plants, eliminating pesticides, reducing garden disturbance, controlling our use of mulch, and changing human notions about native insects.
- A garden full of locally native plants provides food and shelter for native insects.
- A hard look at pesticides reveals that nearly all are used against non-native insects that feed on non-native garden plants. A native garden, then, has no need for pesticides. The insects that show up to feed on those native plants belong there.
- Soil cover (mulch) is often overused. Sure, it helps keep weeds down, but it also covers the bare soil required for nesting by many species of native bees, egg-laying by grasshoppers, and soil pupation by many species of moths and beetles. Try to keep at least some areas of undisturbed bare soil to allow these insects to survive.
We must change the all-too-common human perception that having insects on our plants is a bad thing — it’s not. Enjoy the insects!
Robert L. “Bob” or “BugBob” Allen has studied insects and plants since early childhood in San Juan Capistrano, California. He is now an adjunct professor of biology at Santiago Canyon College and Orange Coast College, a research associate in entomology at the Natural History Museum of Los Angeles County, a research associate at the Rancho Santa Ana Botanic Garden, a horticultural consultant, and author of Wildflowers of Orange County and the Santa Ana Mountains.
We tore out the water wasting lawn and planted manzanita and ceanothus. The California poppies came up by the thousands and the bees really enjoy them. We trained a honeysuckle over an arbor for the hummingbirds. The back yard has dill weed and narrow-leafed milkweed. Butterflies flit through from the nearby dill patches. The tomatoes host tomato hornworms and the Monarchs like the parsley flowers.
I am growing A LOT of speciosa, upon which I’ve gotten monarch caterpillars before. I need to know what nectar plants they like, do you have any suggestions?
Hi Janet. Glad to hear about the showy milkweed (Asclepias speciosa) you have planted! Check out the new Butterfly feature on Calscape.org to find plants native to your location that support local butterflies.
Try pincushion flower (scabiosa) and cosmos. They like the parsley flowers and anything with a flat umbel. My Buddleja attracts everything!
Try pincushion flower (scabiosa) and cosmos. They like the parsley flowers and anything with a flat umbel. My Buddleja attracts everything! Another good idea is Monarda.
I have a blank front yard. The yard is postage stamp size. Not large. I do have fruit trees in the front. Nectrine, peach, orange trees. In the fall, I would like to plant native plants.Suggestions would greatly be appreciated. I enjoy the fruit I get from the trees. So, not sure if I want the bugs to eat them.
Hi Linda. Glad to hear you are planning to plant natives in your yard! Since native plants and native insects co-evolved, native insects will most likely look for native plants for food – not non-native fruit trees! Planting natives will likely attract pollinators that may increase pollination and thus yield on your fruit trees. Check out our Native Landscape Planting Guides to get plant and landscape design ideas for your region. Also, be sure to visit Calscape.org to discover plants native to your location.
How do we help with the cooling of our neighborhoods? Cement, housing, fake lawns? The story about the permafrost was so interesting. To bad the human race isn’t helping with our climate, except to continue to cover the earth. Suggestions!!
Hi Linda. If you live near Mountain View, check out this talk on Sept. 12 on gardening to help with global cooling. https://www.facebook.com/events/2373406302735333/
Can you give me the best method to germinate the seeds that I purchased from SNPS-SD Ca Native Seeds.
It is July and I have put the seeds (not needing strafication) on damp soil and have the containers covered and on heat mats. It’s been 3 weeks and now I’m second-guessing myself. Maybe the Native seeds need to be outside either in shade or sun. Can you give me hints at how to have some successful germination?
I have Nuttall’s Snapdragon Broadleaf/Riverbank Lupine, Red Bush Monkey flower, Silver Lupine, Fremont’s Star-Lily.
Hi Molly! This is Cindy from CNPS-SD Seeds & Bulbs. I’m sorry to hear that your seeds are germinating! While it’s not uncommon for one or 2 species not to pop up, when none of them come up it is worth being suspicious of the technique. In general I wouldn’t recommend heat mats for natives. I actually recently tested the temperature on one and it got up to 90 degrees (they tend to raise the temp 15 degrees above ambient). Holding seeds at that fixed temp doesn’t mimic their natural germination conditions and at will actually cook them at high enough temps (and you mention a cover – which if super tight might not let in oxygen). This gets me to my general soap box summary of how to start native seeds: by all means experiment but your best bet is to mimic the natural conditions the seeds might see in the wild. In CA, and for the plants listed above, that means going to seed in the heat of summer, maybe lying around on top of the dirt exposed to sun for a few months, and then slowly being hydrated in late fall when still warm during the day but when nights are cool. This “diurnal” temperature fluctuation can be key for many plants and shouldn’t be ignored when using temperature controlled devices for germination. Some species need that solid month or so of deep cold first to break the germination lock and it is worth trying a week or 2 in the moist soil in the fridge when all else fails. Lee Gordon has also reported that some seeds seem to benefit from sitting out in the hot dry sun before planting. In the case of lupine seeds, they may travel through the gut of a bird or get scratched up (aka “scarified”) making their hard seed coats more ready to take up water. The snapdragon and monkey flower seeds are sooo tiny they can easily be buried too deep in the soil and not find the light of day. So… my recommendation? Ever so lightly sprinkle seeds on clean dirt in pots in dappled sun and mist 1-2x per day. If they don’t come up in the summer, consider waiting until fall or try a few of the other tricks up the germinators sleeve. There are a few references I’ll try to look up and post here in the next day or two. Hope that helps.
Hello me again… here is a great reference for different propagation techniques from the Santa Barbara Botanical Garden and reposted on Calscape. See in particular section four on Seed Dormancy and Treatments. https://calscape.org/seed_propagation.php
The grounds committee of a 40 year old Home Owners Association in Mountain View, CA is looking to introduce native beneficial plants and shrubs especially under 40 year old clumps of Redwood trees. The ground unfortunately is mostly root bound and covered with ivy that was also planted 40 years ago when the property was first developed.
One idea was to use 30 gallon planter barrels with the following selection of plants/shrubs
1) Flowering shrubs: Western Spicebush (Calycanthus occidentalis) Bright green aromatic foliage with interesting maroon-red flowers in spring-summer that resemble small water lilies and have a wine-like fragrance. Another option is Western azalea (Rhododendron occidentale): beautiful white springtime flowers, deciduous
2) Ferns: Western five finger fern (Adiantum aleuticum) > Western sword fern (Polystichum munitum) > California maidenhair fern (Adiantum jordani). Avoid Giant chain fern (Woodwardia fimbriata) it grows too big
3) Berries: Prefer Thimbleberry (Rubus parviflorus): woodsy edible berry, perennial on thornless canes in a dense shrub up to 2.5 meter tall often growing in large clumps.
Any feedback would be greatly appreciated.
Huckleberry should do well in dappled shade. Pretty glossy leaves and lantern shaped blossoms. Tasty berries.
If you want to help monarchs, you have to plant native milkweed, showy or narrowleaf. You also have to plant nectar plants, here’s a great list from Xerces Society: https://xerces.org/publications/plant-lists/monarch-nectar-plants-california
Helebore, cyclamen and dicentra would be pretty if you are willing to rip out some
of that ivy,
There is a lot of that fragrant white azalea along Soquel Creek with tiger lillies, Very pretty combination.
If you are going to use the barrel planters. how about a couple of filberts? Tasty nuts, but the animals and birds are going to eat most of them. Velvet leaves and a charming horizontal arrangement of branches. Stays small.
The listed plants won’t help monarchs. They need showy or narrow leaf milkweed as host plants (for egg laying and larva). They also need nectar plants- Native asters, goldenrod, yarrow, ceanothus, mor listed at xerces.org.
All of these are nectar flowers for monarchs.
This is a great source for info: https://xerces.org/pollinator-resource-center/california
At Tahoe we saw a small bush called Serviceberry with small white flowers. Here again, you won’t see much fruit, the critters gobble it all up.