What is green mulch?

We all know what mulch is – it’s that stuff we pile around our plants to prevent any other plants from growing. That’s good, as far as it goes. But mulch is pretty limited in its ability to provide any other benefits to our gardens. And the need to constantly bring in more mulch from off site creates a variety of costs. Is there a better, more multi-functional way we can stop unwanted plants from sprouting?

Enter green mulch.

“What stops plants from sprouting?” some inventive gardeners asked themselves. One answer is herbicides. Another answer is the absence of sunlight, water, and soil. But a third answer is other plants. In general, a plant simply can’t grow in a space already occupied by another plant. And so these creative gardeners came up with a simple strategy: to keep out plants you don’t want, fill all the available growing space with plants you do want.

Well, how do you that? The trick is layers. In order to create a planting so dense that nothing new can squeeze its way in, the members of that planting community must grow in a variety of shapes and sizes, so that they fit around each other, leaving no room for anything else. A monoculture – of pine trees, corn, bluegrass, or anything else – will always be made up of repeating plant shapes with predictable gaps that can easily be colonized by opportunistic newcomers.

And in a dense, layered planting, gardeners have discovered that the real gatekeepers are the lowest-growing species. Trees, shrubs, and other tall plants will always have open space underneath that unwelcome guests can sneak into. In contrast, plants with a creeping habit – that is, plants that spread along the ground, putting a few leaves into any available spot and then stretching onward to the next opening – efficiently cover soil, making it very difficult for any arriving seeds to germinate and get a foothold on a new life.

This is green mulch – living plants that take up space and crowd out unwanted interlopers. It serves this purpose just as well as traditional mulch, while involving less long-term cost and maintenance, and providing a host of additional benefits associated with healthy plants.

Wherever you live, there is sure to be a native plant that will happily serve as your green mulch. These little plants may not be eye-catching showstoppers, but they pull their weight in the garden, helping the community as a whole to thrive.

What is green mulch?

What is a green roof?

The conventional approach to gardening has been to place a few “landscape” plants in the yard, then fill all the remaining area with lawn. The recent film Hometown Habitat advocates a different approach: deciding where people will need to walk or run or play, putting lawn there, and densely planting everywhere else with naturally-growing trees, shrubs, and flowers. Some people take this idea seriously by packing plants into every available space on their property, including on their roof. The result is called a green roof.

Aside from creating more room for plants to do all the wonderful things that they do, putting a garden on the roof creates some special benefits. First, it converts a typically impermeable area into a space capable of absorbing water. Thus, green roofs reduce runoff and flooding. Second, plants and soil are an excellent form of insulation, keeping the building below the roof both warmer in the winter and cooler in the summer. Third, far from damaging a conventional roof, a well-designed planting actually protects the roof underneath and extends its lifespan.

Of course, you can’t get these benefits just by climbing up on your shingles and scattering some seeds. A functioning green roof requires a little bit of planning and knowledge.

First, the aspiring roof gardener must check that their house, garage, apartment complex, office building, or other structure will be able to hold the weight of a planting, with all its supporting layers.

Second, the gardener must familiarize themselves with those layers: a roof garden consists of plants, of course, but those plants must be rooted in soil. A green roof, due to the challenges of weight constraints, doesn’t use soil dug up from the ground below, but rather incorporates a special lightweight planting medium. Below this is a root barrier, to prevent plants from growing too far downwards and working their way into places that are not improved by their presence. Next comes a drainage layer, to ensure that any water not absorbed by the plants will be channeled safely to the ground. Below that is an insulation layer, and finally a waterproof membrane, to make absolutely certain that no water will penetrate into the building underneath.

Finally, with all of that accounted for, the gardener must turn their attention to the most vibrant layer: the plants! A green roof can include more than just tough, low-growing groundcovers, but it won’t provide a suitable home for every kind of plant. The gardener must choose plants that can withstand the challenging conditions on a roof, such as harsh sun, strong winds, and only a few inches of soil.

Putting plants on a roof may seem like a crazy new idea, but in fact – as with many sustainable ways of living – it’s simply a return to the way things were traditionally done. In Iceland, houses were constructed with turf roofs for over 1,000 years, in part because of the superior insulation offered by sod against the frigid climate. This practice continued well into modern times; examples of turf houses can still be seen in Iceland today.

turf houses

What is a green roof?

How can one yard make a difference?

In some respects, sustainable gardening is what’s known as a collective action problem: a challenge in which many people need to work together to enact a solution, and in which the first few people to act incur high costs while receiving few, if any, benefits. These problems are difficult to solve because everyone needs to act, but no one wants to act first.

In the case of sustainable gardening, the first person on the block to plant native wildflowers, or not rake their leaves in the fall, or even just set their lawnmower blade to four inches high (it really is better for the grass) could end up getting criticized – or worse – by their neighbors, while the positive impact they’re having on the environment seems like hardly a drop in the bucket compared to the serious problems our planet is facing. Under such circumstances, who would want to be a trendsetter? Even if our neighbors nod politely at our efforts, isn’t one yard just too small to make a difference?

That Blogger had an opportunity to put these questions to Doug Tallamy, a professor of entomology at the University of Delaware and a well-known advocate of natural yards, just a few months before That Blog was launched. Here are his answers.

Can one yard make any difference to nature?

Less than one yard can make a difference, Tallamy said. Even a few flowers on a balcony or in a window box can provide a valuable foraging stop for butterflies and other pollinators. And a space the size of a bedroom can have real, measurable benefits for these small creatures. A 15-by-15-foot garden in the completely enclosed courtyard of the Department of Agriculture building in Dover, Delaware, became a nursery for no fewer than 150 monarch caterpillars, when employees in the building simply chose to use that space for milkweed rather than for grass.

What if we just don’t put nature in our yards?

“We no longer have the option of opting out,” Tallamy said bluntly. “Most people do not have viable habitat [in their yards], and we’re seeing a steady drain of species from our ecosystems.”

As those species vanish, the ecosystem services they provide disappear too. That’s a serious problem for us humans, Tallamy said. If we want to safeguard our own survival, we need to do something now. Once the species we exclude from our yards are extinct, we can’t bring them back.

Do enough people have nature in their yards?

No, Tallamy said. But we’re getting closer to the critical threshold of solving this collective action problem.

Sustainable gardening is “certainly not mainstream yet,” Tallamy said (speaking in early 2015), “but it’s headed in that direction. I’m optimistic. We have turned the corner much faster than I thought we would have.”

But seriously. One yard?

Tallamy turned the question on its head, pointing out that regardless of property lines, we don’t need to think in terms of just one yard. Our next-door neighbor has a yard. Their neighbor on the other side has a yard. There are yards all the way down the block and into the next town and across the country. We can invite all of those neighbors to join us in our efforts to garden with nature. We can encourage landlords of apartment buildings to landscape their grounds with native plants instead of with lawn. We can pressure our local officials to plant more street trees and spray fewer pesticides.

When we have the courage to be a trendsetter, we are not small. And we can make a difference.

How can one yard make a difference?

Why is That Blog necessary?

That Blog has now been active for three years, and currently has nearly 200 posts. Those posts document numerous benefits of natural yards, and also report on clear signals that the era of the lawn is rapidly coming to a close.

During that same three-year period, however, the acreage of lawn in the United States has continued to increase, alongside ongoing suburban sprawl, as lawn remains a default landscaping choice in many parts of the country. And, studies still find that many people do not understand or value the many crucial services that urban nature provides for us.

A fascinating report from 2015 – just after That Blog was launched – investigates why experts on the importance of urban nature struggle to communicate what they know to laypeople. The fundamental finding of this report is that while experts recognize that nearby nature is absolutely critical to human health and wellbeing, the average person views nature as a sort of bonus amenity that is nice to have around if there is any space left after inserting houses, schools, workplaces, roads, parking lots, and all the other manmade infrastructure a community needs.

The report finds that many people also struggle with the basic idea of nature in cities. Urban dwellers often don’t view their local parks as nature, despite the presence of trees and other plants. To many Americans, “nature” means someplace vast and far away, the kind of place we visit occasionally on vacation.

In other words, the average person thinks that nature only counts if it’s big, and that we can “stock up” nature to sustain our wellbeing throughout the year. In contrast, experts understand that people benefit from nature as small as a pocket park or a residential yard, and that we need daily exposure to nature to really be at our best.

After comparing the views of laypeople to the knowledge of experts, and examining the communications gap between the two groups, the report concludes that people would value and support urban nature more if they understood that:

  • nature benefits us even when it is small.
  • we benefit from experiencing nature, rather than simply using it as a place to take a walk and get exercise.
  • nature benefits us in specific ways, via mechanisms science can explain.
  • nature is an essential component of urban design; we cannot live without it.
  • we can choose to have more nature in our cities!

For three years, That Blog has examined how even a small planting provides a wide variety of benefits, explored how we feel when we look at naturally-growing plants, explained how plants support our physical and mental health, expressed that natural yards are a great choice for our neighborhoods, and encouraged everyone to garden sustainably with nature!

Until public understanding and acceptance of urban nature is in line with what experts have long known, That Blog is still necessary. In the coming months, That Blog will cover the impacts of global warming, how to be a good neighbor to plants, and what happens to people’s wellbeing when nearby nature is destroyed. But first, That Blog will tackle head-on the key question: How can one yard make a difference?

Why is That Blog necessary?

What is an invasive species?

In the last post, That Blog asked what a native plant is. Asking what an invasive plant is might seem redundant – if it’s not native, it must be invasive, right?

Actually, no. If it’s not native, it must be non-native. But not all non-native plants are invasive. An invasive plant is one that meets a special definition:

An invasive plant is one which tends to spread, and which causes harm to the local ecosystem.

A non-native plant that stays put in a garden, or that escapes into the wild but causes no discernible disruption to the existing plant community, is not considered to be invasive.

Where do invasive species come from? Some – like Kentucky bluegrass – arrive by accident, as stowaways in other shipments. But half or more of the invasive species spreading across the United States today were deliberately introduced by the nursery trade. People planted these ornamental exotics in their yards, and the plants then cheerfully multiplied beyond the property lines.

In recent years, some states have tried to deal with this problem by banning the sale of invasive species. Some of these measures have passed; others have not. Even when they do pass, though, they tend to ban plants which have already been sold in abundance, and which have already spread into natural areas. Once a species has invaded an area, it is usually very difficult to eradicate. Banning the continued sale of such species is unlikely to make a dent in the problem.

An approach that might be more effective is to make every property owner responsible for eliminating invasives from their own land: if we each take care of our own piece of the Earth, together we might be able to accomplish something. Municipalities have used this approach for a long time, in the form of banning so-called “noxious weeds”. But these weed bans are often not enforced, and, more importantly, they tend to take aim at plants that are unpopular, rather than focusing on plants that are truly harmful. As just one example, these rules often forbid milkweed, the family of native flowers that are crucial to the survival of the monarch butterfly.

Before we pause to reflect on That Blog’s third anniversary, let’s take a look at one more definition worth knowing: a naturalized plant is not one that has settled harmoniously into its new home. Rather, it is a non-native species that is capable of surviving and reproducing without human help; in other words, a species poised to become invasive.

What is an invasive species?