Red Ink, Green Joy

Lunaria annua (Money Plant),
by Christian Fischer

On my soggy drive home today, talk radio was filled with opinions about the pending "economic stimulus package" and the looming recession driving it. Lots of doom and gloom, both here and abroad. And it got me thinking (as most things do) about gardens and the people who live with them.

On the one hand, a well-designed garden is a true luxury: it doesn't shelter us from these incessant rains, it doesn't furnish us with cotton or wool to spin into garments. It costs money to design, money to install, and money to maintain. The average bribe rebate from our government will be something like $1600, which will hardly buy you a yard full of gorgeous plants, much less my design fees to wrap them up into a dramatic and fabulous package. Let's face it, you need a custom garden about as much as you need quilted teddy bears on your bath tissue.

On the otherhand, a well-designed garden may be an absolute necessity, especially in darker times. It can save you money on energy and water through intelligent planting design and efficient irrigation and lighting. It can lower your grocery bill by providing physical sustenance, i.e. delicious fruits and vegetables, every month of the year. But most importantly, it can bring you joy every day by creating an environment filled with vibrant colors, intoxicating scents, soothing sounds, bejeweled birds and butterflies, or those priceless spaces where your children can play or you can relax.

So what would I advise to someone who wants to upgrade their landscaping, but isn't sure now whether that's such a good idea? Obviously, I can't tell anyone how to prioritize their budget, and I certainly don't advocate going deep into debt with a landscaping project. But given that it is a short-term investment in your spirit as well as a long-term investment in your most significant asset, maybe — just maybe — a well-designed garden is a luxury you can't live without.

Mad for Moss

Maybe I've been watching too much NFL, but with Randy, Santana, Sinorice, and Jarvis all hogging the headlines, it's no wonder I've got moss on my mind. But I'm not thinking about the 200-pound, fast-as-lightning gridiron gods; I'm thinking about the tiny green stuff that ever so quietly blankets the masonry and glows emerald in the morning light.

And I'm thinking about it because it's time to give my urbanite retaining wall a little verdance of its own, and there's nothing like the green patina of moss to create a feeling of age and presence. But where to start?

Online, there's a lot of talk about moss, but fairly little detail. To create the slightly acidic environment moss prefers, some people recommend blending samples of moss along with some buttermilk, then painting the resulting slurry onto the desired surface. Others recommend using beer instead of buttermilk. Still others recommend beer and buttermilk. There's also advice to just lay the moss down like miniature sod, and even to use super glue.

Not wanting to introduce cyanoacrylate into my garden, I think I'll stick with the Osterizer approach. But which additive? How much? I certainly don't have a definitive answer, so I'm going to try a few different approaches and report here on the progress. I've also read that potter's clay or a water retention gel can help the mixture adhere to a rocky surface, so I might try either that (or perhaps some of my clayey garden soil).

My first step is to collect some mosses that are growing locally, in conditions and locations comparable to my intended target. It doesn't get much more local than the front walk of the house across the street, as well as the driveway and Quercus lobata next door. I'll use a putty knife to scrape the moss up, "roots" and all, then divide it up into portions and blend each into a different recipe. Then I'll use a paint brush to spread the mess onto my rock wall… and wait!

Benefits of a Rain Garden

The whole reason I'm installing my vernal pool, or rain garden, or whatever it is, is to restore a little bit of natural ecology as well as reduce the amount of urban runoff into our storm drain systems.

"But, John," you protest, "how much runoff are you really eliminating with your little 110 square foot pond?"

Glad you asked. Hey, math time again!

110 square foot pool surface area
* 1 foot average pool depth
__________
110 cubic foot pool volume
* 7.48 gallons / cu. ft.
__________
822.8 gallon capacity
* 66% full
__________
543 gallons

That's right, in Friday's storm my little pond held well over 500 gallons of rainwater — not counting what it percolated during the storm — and ultimately released it back to the earth rather than letting it flow out to the gutters or dumping it out at my home's foundation, whether into a French drain or not.

543 gallons and counting? I'm feeling pretty good about myself right now.

Rainy Day Math Fun

Well, wasn't that refreshing?! Nothing like two inches of solid rain to wake up the winter, and more is coming down today. It's the perfect test of my vernal pool, which began filling around 8 a.m. yesterday and ultimately filled to about 6" below capacity within 12 hours. The water comes primarily from our roof, with about 2/3 of its downspouts tied into a central outlet at the mouth of the pool. (The other downspouts let out onto the permeable driveway, so there's some percolation, although I intend to tie those into the pool as well.) There also was some water siphoned in from drainage problem areas in the back yard, but probably less than 20 gallons.

A couple of things were really amazing to me. The first is that my math was more or less right! Assuming a maximum daily rainfall of about 1 inch (not quite the record, but also above the norm), I wanted the pool to hold all the runoff from my 1200 square foot roof. Ready for some algebra? Follow along:

1200 square feet
* (1 inch of runoff ÷ (12 inches/foot))
___________
100 cubic feet of runoff capacity needed

So I built the pool's surface area to about 110 square feet, at an average depth of about 12":

110 square feet
* (12 inches ÷ (12 inches/foot))
___________
110 cubic feet capacity

Sure enough, this storm dumped 2 inches of rain; and again, the pool collects about 66% of the roof area:

(1200 sq. ft. * 66%) = 800 sq. ft.
* (2 inches ÷ (12 in./ft.))
___________
133 cubic feet of runoff

But wait! Why didn't the pool overflow? Ah, let's not forget about the soil's absorption capacity. My soil isn't completely compacted, so it should still percolate at a rate of at least .75 inch per hour (not that I've actually tested it yet). We don't know the rainfall rates per hour; we do know the day's average was 2" over 24 hours, so let's assume it fluctuated between 1/16" and 1/2" per hour. The pool was receiving those rates (depths) of rain across its 110 sq. ft. area, as well as the 800 sq. ft. of roof.

800
+110
___________
910 sq. ft. total surface area

To determine what percentage of "its own" area the pool was receiving:

910 sq. ft. total area
÷ 110 sq. ft. pool area
___________
8.27

The pool was receiving 8.27 times, or 827%, of its own area. Multiply that by the rate (depth) of rain to find out what volume it was taking on:

8.27 * 1/16" per hour = .52" per hour (assumed minimum flow into pool)
8.27 * 1/2" per hour = 4.14" per hour (assumed maximum flow into pool)

This means at the peak periods, precipitation was outpacing percolation by about 4 inches per hour. That's why the pool filled as much as it did. But that was a small minority of the time: more often, percolation outpaced precipitation by .25 per hour... and that's why the pool never overflowed.

(Knowing that the pool takes on 8.27x its area, we can also determine the "equilibrium" rainfall rate:

.75"/hour pool percolation rate
÷ 8.27
___________
0.91"/hour precipitation rate)

(By the way, the second amazing thing to me was that, after about 12 hours of no rain, the pool had no water this morning. Let's see what the fill/percolation rates are today, now that the soil is saturated.)

This kind of math is what landscape designers and architects have to do all the time in designing drainage systems, water retention basins (like vernal pools), even landscape irrigation systems. It's a lot more complex than just this algebra, but I hope it shows a little bit of the "behind the scenes" work we do — it's not all just pretty pictures.

If you've hung on this long, you're probably doing the math yourself. Please correct me if I've missed something, or feel free to ask questions. It's been a fun rainy-day diversion.

PS: This whole episode has alerted me that I might consider renaming my little water feature. Technically, a vernal pool has the geographic feature of a semi-imperpeable "pan" beneath the grade which slows drainage throughout the winter and spring. Mine, obviously, drains fairly readily; so I suspect rain garden — although becoming nauseatingly trite — may be a better description. Stay tuned.