Gardening season is upon us in northern New England. After another weird winter characterized by a series of freezes and thaws, and then a late winter rally of cold and snow in March, spring seems like it is finally here to stay. When considering perennials to enrich our landscape, the array of species at our fingertips is staggering. A trip to the local nursery will expose us to an impressive array of glossy-leaved, long flowering, insect-resistant plants from all over the world. Some of the most popular perennials are genetic anomalies, having double flowers, or leaves and/or flowers that are a different color than the original plant. In the case of double flowers, the pistils and stamen, the nectar and pollen producing parts, are replaced with showy petals. This renders the plant useless to pollinators like bees and butterflies. Right now your local nursery may be selling a sterile double-flowered bloodroot, a sumac with purple leaves, or an Echinacea with lime-colored flower petals.
Bumblebees and butterflies love Liatris pynostachya (Prairie Blazing Star)!
Despite all the eye candy available to us, many gardeners are starting to think more broadly when we plan our gardens and landscapes, beyond just aesthetics. Alongside our personal needs for food, medicine and beauty, the plants we grow can also serve the creatures that share this earth with us. The plants can provide food and shelter for pollinators, amphibians, reptiles, mammals, and birds! Essentially our built landscapes can be vibrant, buzzing ecosystems that mimic the productivity and beauty of wilderness.
Not only is it possible for our gardens to provide important ecosystem services, it is imperative that they start doing so, as there is just not enough protected land on earth to slow or stop what some people are calling the 6th great extinction. Below are some very sobering statistics. Don’t get discouraged. There is definitely something we can do about it!
Studies of ecosystems have revealed that there is a 1:1 correspondence between habitat loss and number of species. That means that 50% loss of habitat will eventually result in a 50% loss of species! When habitat is lost, some indigenous species will disappear immediately, others will slowly decrease in numbers. With that in mind, it is estimated that 95-97% of all land in the lower 48 of the United States has been significantly altered, including approx. 50,000 sq miles of asphalt roads (5.5 times the size of New jersey), 40 million acres of nonnative lawn grasses (8 times the size of New jersey). 41% of our land is in agriculture, 54% is classified as cities and suburbia. The remaining preserved land is fragmented, and habitat islands have high rates of species extinction and emigration and low rates of species immigration and new species development. If habitat is not restored we will continue to see massive losses in plant and animal populations, as well as an accelerated rate of species extinction.
A recent study adds an exclamation point to our need to start thinking about being better stewards of the land. Analysis of extensive data by scientists at the World Wildlife Fund and the Zoological Society of London has revealed that the earth has lost half of its wild animals in the last 40 years! This steep decline was spread over both terrestrial and marine habitats, with freshwater ecosystems seeing a particularly sharp decline. The animal, fish and bird numbers were calculated by analyzing 10,000 different populations, covering 3,000 species in total. It was determined that habitat loss and degradation is responsible for almost half of this loss.
Now imagine that just half of the 40 million acres of US lawns were converted back into viable animal and plant habitat, in the form of native plant gardens. That would cover an area equal to nine Yellowstone National Parks. More importantly, that new habitat would be spread all over the nation, creating habitat bridges for a diverse array of ecosystems.
A Clouded Sulphur taking advantage of a mid-autumn bloom of New England Aster (Aster novae-angliae) flowers. The larval stage of this insect can only eat plants in the Fabaceae (Pea) family.
There are many known benefits of biodiversity. For one, more biodiverse ecosystems are more productive. They capture more energy from the sun, turn that energy into more insects and animals, sequester more carbon, filter more water, and produce more oxygen. Diverse ecosystems also prevent pest outbreaks, and deter invasive species. There simply isn’t space for invasive species to take over when all the ecological niches are filled by diverse, competing organisms. Biodiverse ecosystems are also much more stable than simple ones. If one species is lost from the food web, the web will not collapse, as another species will step in to do the job. One of the easiest ways for gardeners to contribute to the food web and increase biodiversity in their landscapes is to plant native species. As you will see below, native plants are critical components of a functioning ecosystem.
Studies have shown that native plants support many times more insect biomass than alien species, including 4 times more insect herbivore biomass, and ~3 times more overall species. One of the most compelling reasons to promote native plants is that 90% of herbivorous insects are highly specialized and require one genus or just one plant species to survive. It takes millions of years for most insects to adapt to the specific chemical deterrents that are present in a particular plant or group of plants. Essentially, if you take away the host plant you lose the insect species that has adapted to its unique chemical composition. Only 1% of the 4 million insect species are “pests.” The other 99% pollinate plants, turn dead plants and animals into compost, prey on insect herbivores, aerate the soil, and are a critical food source for birds and other creatures.
In turn, 96% of terrestrial birds feed their young exclusively on insects and spiders, with Lepidoptera (butterflies and moths) larva making up the bulk of food. Take away the insects and you take away the birds. It has been found that locally-adapted plants support a whopping 35 times more Lepidoptera biomass! Amphibians, reptiles, and small mammals also largely depend on insects.
Wild Bergamot (Monarda fistulosa) is a favorite source of nectar for Fritillary butterflies. However, their larva only eat plants in the Viola (Violet) genus.
A classic example of insect specialization is the monarch butterfly. The sticky latex sap in Milkweeds contains cardiotoxic cardenolides that will kill most insects, and the gum can glue together an insect’s mandibles. Monarch caterpillars have learned to drain some of the latex out first, and evolved sodium/potassium pump enzymes that are not destroyed by the chemical. This prevents the life-threatening circulatory system damage that would befall other insects. Monarchs also store the cardenolides in their body to make them toxic to predators. Other examples of specialization are fritillary and pearly crescent butterflies. Fritillary larva only eat violets (Viola spp.), and pearly crescent butterfly larva only feed on smooth leaved aster species such as Flat-Topped Aster (Doellingeria umbellata) and Smooth Aster (Symphyotrichum laeve).
A honeybee on Echinacea purpurea. Populations of native bees due tend to decrease when non-native honeybees are kept nearby.
Focusing your gardening efforts on supporting pollinators, like native bees and butterflies, is a great place to start, since bees are responsible for the majority of pollination services needed by plants, and because birds depend on moth and butterfly larva to feed their young. Choosing a number of plants, that have a variety of flower types, and that bloom successively throughout the whole growing season, is important for getting the maximum number of species to stick around. Butterflies and moths have a long proboscis and so reach isn’t a problem for them. However, most of them do not hover to feed, so they need a landing spot. Many plant species have evolved wide landing areas that accommodate this need, such as Echinacea spp, Rudbeckia spp, Goldenrods, and Liatris spp.
A mining bee making her way over to a stunning display of Penstemon calycosus (Calico Beardtongue) flowers.
There are over 4000 species of native bees. The small, short tongued bees, such as sweat bees, can only reach into shallow flower tubes. They favor plants like Culvers Root (Veronicastrum virginicum), Coreopsis spp, Asters, and the Mountain Mints (Pycnanthemum spp). Flowers with longer tubes, like the penstemons, columbine, Monarda spp, and Virginia Bluebells (Mertensia virginica) are favored by medium- to large-size bees and bumblebees, whose tongue length usually corresponds to body size.
When creating pollinator gardens it is important to consider the full life cycle of our native bees and Lepidoptera. 70% of our native bees nest in the ground in bare or sparsely vegetated soil. Most of the rest tunnel nest in dead standing trees (snags) or in dry plant stems. Different species of Lepidoptera overwinter as eggs, caterpillars, pupa, or adults. Bumblebees nest in abandoned mouse nests, under hummocks of dead grass, and in tree cavities. Brush piles, bare ground, and dead standing vegetation are all important habitat. A tidy yard is of little use to wild creatures. Letting dead perennial stalks stand throughout the winter will preserve insect habitat and give birds access to seeds that will often persist throughout much of the fall and winter. A dead standing tree can support as much or more life as when it was alive.
A tiny native bee (possibly a type of sweat bee) enjoying a late September feast on a relatively giant Oxeye Sunflower (Heliopsis helianthiodes). Sweat bees are ground nesters and need patches of dry, bare soil to build their tunnels. If you have habitat like this on your property consider preserving it for the bees, as 70% of our native bees are ground nesters.
There are several approaches to getting to know what is native in your region. A trip to your local library or bookstore may be in order, as there is an increasing amount of literature on the topic. Native Plants of the Northeastby Donald J. Leopold is good start for those of us who live in New England. Taking plant walks with a knowledgeable herbalist or botanist and/or a trusty plant guide is probably the best way to get to know the native, naturalized, and invasive species in your region. An excellent plant guide for the eastern US is Newcomb’s Wildflower Guide. Not all of their plants may be native to your particular area, so it’s important to do further research before you choose your plant list. I find the online databases for the Missouri Botanical Garden and Lady Bird Johnson Wildflower Center to be particularly useful, along with wikipedia. Prairie Moon Nursery has an excellent website, with a long list of plants native to the midwest and east. They include range maps, so you can see if the plant you are interested in is native to your particular area.
Native plant nurseries are popping up all over the country. If you have a local nursery, and if they use local seed stock, you are probably in the best position, ecologically speaking. A plant of the same species with Michigan genetics is bound to differ a bit from a plant with Vermont genetics. It may bloom at a little later, have leaves that are more or less hairy, and/or have a slightly different chemical make-up. This may or may not make a difference to your local insect and animal herbivores. If local ecotypes are not available, do not fret! Wild geranium from Minnesota is likely to deliver many more ecosystem services in your Massachusetts shade garden then a hosta from Japan.
I prefer landscape plugs for woodland plantings and small, more formal meadow plantings. They are grown in deeper pots, and have more established roots than normal plugs. They also need less watering to get established. Landscape plug packs are usually available in late spring/early summer. Preorder to make sure they don’t sell out of the plants you want.
For larger meadow plantings it is much more cost effective to sow your seeds directly into the ground. Some of the better nurseries, like Prairie Moon, have expertly crafted seed mixes. They often contain 20 or more species of wildflowers and grasses, and are designed to provide sweeps of color and food for wildlife throughout the growing season and then into the fall and winter as seed heads mature and ripen. The best time to sow seeds for most species is late autumn, as most seeds need a period of cold, moist stratification before they can germinate, and there is no better way to do that than the outdoors. If there is danger of the seeds washing away, as on a slope, it may be better to cold stratify the seed in the fridge. Follow instructions from the seed supplier.
Before any seeds can be sown, the ground must be prepared. You can do this by tilling the site regularly during an entire growing season, spring through autumn. The first till should be deepest, as you are trying to unearth the deeper roots of perennials and biennials. After that it is best to till more shallowly, just a couple inches. A hoe can be used for this stage if the area is not too big, or if you want to get a lot of exercise. Shallow tilling will stimulate all the “weed” seeds stored in the top few inches of soil to germinate. If you do this repeatedly throughout the growing season, you will exhaust and flush the weed seed bank. This will eliminate the competition for your meadow species, essentially giving them a competition-free blank slate. If you do notice undesirables growing amongst your meadow plants it is better to cut them to the ground than to pull them up by the roots, in order to avoid bringing up additional weed seeds and to prevent root damage to the species you are trying to get going.
Before I wrap up this posting I’d like to share a couple tips for success with native plants. First, it is important to get to know the soil and moisture conditions of your site. However, instead of amending the soil to improve fertility and drainage, you’d actually do better to keep things as they are. This goes against conventional gardening wisdom, but there is no better habitat for all kinds of weeds than rich, well drained garden soil. It is better to find plants that match existing conditions. Very wet, very dry, heavy clay, and sandy soils tend to favor native plants over invasive species.
In a woodland or meadow plant community, nature does not waste space or time. Different plants often occupy the same space throughout the growing season. For example, in a healthy forest, the spring ephemerals like ramps (Allium tricoccum) and trillium species will first cover the forest floor, followed by plants that peak in midsummer, like Solomon’s plume (Maianthemum racemosum) and Doll’s eyes (Actaea pachypoda.) In the fall the woodland asters and goldenrods dominate. Suddenly, when everything else dies back, the ferns and mosses become evident. The different needs of the members of this plant community allow them to live virtually on top of each other, but without competing for the same resources. As a matter of fact, many plants, especially ones that evolved together, have symbiotic relationships with each other. Trying to mimic these kinds of patterns in your gardens will bring greater success and satisfaction, as well as a deeper understanding of the living, breathing, incredibly complex natural world that surrounds us.
Erin Keith O’Hara runs Turtle Hill Native Plants in East Monpelier VT. He lives in a tiny house amidst giant gardens.
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