Cushion Plants and Species Richness

Cushion plants are in the news. A study published in the journal, Ecology Letters, has demonstrated that cushion plants can help increase species richness (the number of unique species in an ecological community) by modifying their micro-environment, which in turn allows certain species to exist in the community that would otherwise be unable to survive the harsh conditions. Other studies have had similar conclusions, but what is unique about this study is how extensive it was, involving 77 alpine plant communities on 5 continents.

The term “cushion plant” refers to a specific growth form. It describes a plant that grows low to the ground, has numerous small leaves and a closed, tightly-packed canopy with dense non-photosynthetic living and dead plant tissues below the canopy. Above ground it appears as a lush, thick, spreading, green mat; below ground it has a long taproot and an extensive root system. There are around 338 species of cushion plants, spanning 78 genera and 34 plant families, which can be found around the world mainly in alpine (high-altitude, tree-less) environments. Around half of the cushion plant species are native to the Andes in South America.

So, how are cushion plants able to increase species richness in their communities? There are a few unique characteristics of cushion plants that lead to this result:

– The tightly-packed, low to the ground growth form of cushion plants helps to modify the temperature of the underlying soil, working as a living mulch to keep the ground warmer in the winter and cooler in the summer. Plants that otherwise could not abide in extremely cold soil conditions, can thrive inside of a cushion plant due to this modification.

– The shading and covering of the ground also helps to maintain a higher level of soil moisture below cushion plants, resulting in more available water throughout the growing season, which is especially important during warm months of the year when water becomes scarce elsewhere.

– Cushion plants may also increase nutrient availability in the surrounding soil. This could be due to their long taproots and extensive root systems allowing them to “mine” the soil and pull up nutrients (and water) that would otherwise be unavailable to shallow-rooted plants. It could also be due to the high degree of dead plant material found within cushion plants that leads to an increase in the amount of organic material in the soil below. The warm, moist conditions of a cushion plant’s underbelly could speed up the rate of decomposition and nutrient cycling, making essential nutrients available to plants growing within them.

Because of these features, cushion plants act as “nurse plants” to species that grow within their mats, providing them with more accommodating soil temperatures, greater access to water, and a higher level of nutrients compared to the surrounding open ground. Some of these plant species would have little or no chance of survival in the harsh environment outside of the cushion plant. Cushion plants are also considered foundation species or keystone species because they play such a strong role in structuring their ecological community, affecting the diversity of species found in the landscape and the abundances of those species.

Silene acualis

A common and popular cushion plant: Silene acaulis. Common name: moss campion. Plant family: Caryophyllaceae. Occurs in high mountains of North America and Eurasia. Photo credit: wikimedia commons.

cushion plant as nurse plant

An example of a cushion plant with another plant species growing within it. Photo credit: wikimedia commons.


Seed Swaps

I am a huge proponent of sharing and the free exchange of ideas and items, which is why when I learned that there was a seed swap happening in my current hometown, I was happy to participate.

Seed swaps are events where people can bring seeds that they have either saved themselves (i.e. collected from plants they grew in their garden or found growing elsewhere) or have purchased and trade them for seeds brought in by other participants. Bringing seeds isn’t always a requirement though – in some cases, if you have no seeds to offer, you can take what seeds you need and then plan to bring some to the following year’s swap.

Seed swaps are great ways to be introduced to plant varieties that you may not be familiar with and to get ideas for what to grow in your garden. They are also a huge benefit to people who would really like to have a garden but have limited money to purchase seeds. Another benefit, of course, is that it gives you an opportunity to unload all of your old seeds – seeds that you may no longer be interested in but someone else might.

There are also social and educational benefits to seed swaps. Mingling with other gardeners gives you a chance to meet new friends and learn from their gardening experiences. Depending on the seed swap, there may also be classes and workshops to attend where one can learn more about seed saving and general gardening.

The seed swap that I attended was called Seedy Saturday, and it was hosted by the Treasure Valley Food Coalition. I highly recommend finding a seed swap in your area and giving it a try. If there is no seed swap where you are, start one!


Starting Seeds Indoors: The Planning Stage

It’s February – time to start thinking seriously about this year’s garden. By now you’ve probably received multiple seed catalogs in the mail and you are already starting to think about what you want to grow this year. Now it’s time to think about starting some seeds indoors so that you’ll have some plants ready to go into the garden as soon as it warms up outside. I haven’t had the best luck with starting seeds indoors, probably mostly due to lighting and temperature issues, but hopefully this year will be different.

Something that may be helpful in the planning process is a seed starting chart, which will help you decide when to start each of your seeds. After all, you don’t want to start all your seeds at once because some plants will be ready to transplant faster than others and some plants can be placed outside earlier than others. There are several resources that offer seed starting charts. Two that come to mind are Organic Gardening and You Grow Girl. In order to successfully use these charts, you will need to know the Spring Frost-Free Date for your region. A good place to figure that out is Dave’s Garden.

Once you know what you want to plant and when to plant it, and you have your pots, growing media, lighting, and temperature issues in order, you’ll be ready to go. With dedication, determination, and a little luck, you should have a healthy batch of plants to fill your garden come spring. Happy planting!