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My Mini Rain Garden

September 3, 2017

rain garden siteThe new addition built onto my house three years ago added a feature that my house had never had before – gutters and downspouts. At one corner of the house, near the entrance, I installed a 50-gallon rain barrel under the downspout and attached a small length  of hose which allows me to channel rain water into nearby plantings. By the other downspout, at the west corner of the house, I decided to create a small rain garden.

A rain garden is a strategically placed depression in the ground designed to collect and slowly drain rain water and planted with water-tolerant plants. I don’t actually need a rain garden; my excessively well drained sandy soil slopes away from the house in all directions. Even in the heaviest downpours, water never pools for more than a few minutes. But my hope was that, by creating a depression that can collect and concentrate rain water, I might be able to grow the kind of moisture-loving plant that I normally can’t provide the right conditions for. I had my heart set on a hydrangea.

Last year I did some research on rain gardens, reading both a book on the technical details and the University of Maine Cooperative Extension’s advice. The technical book helped me figure out the appropriate size for my rain garden, which turned out to be very small – a mini rain garden, big enough for one hydrangea.

rain garden preparedThis year, I set out to execute my rain garden plan. My first step was to install a 4’ long flexible extension on my downspout to channel water from the roof in the proper direction. Next, I created a shallow swale to carry the rain water to the lip of the rain garden. I planted some divisions of Geranium x cantabrigiense ‘Biokovo’ in the swale and also along both sides of the downspout extension. This is a groundcover that spreads quickly and grows about one foot high. It should provide an attractive lining for the swale, and my hope is that it will help to camouflage the ugly downspout extension.

With that done, it was time to actually dig out the depression for the rain garden. Because the bottom of the rain garden should be flat, the standard advice is not to build it on a slope, but I didn’t have a choice. This meant that, in order to have the downslope side be at least six inches deep, the upslope side needed to be about two feet deep.  I used some of the soil I was removing to create a six inch high berm around the downslope edges of the rain garden.

rain garden with hydrangeaOnce I amended the soil in the bottom of the rain garden with aged cow manure and compost, I was ready to plant. The hydrangea went in first, planted in the center of the rain garden. I had originally hoped to install Hydrangea paniculata ‘Quickfire,’ a plant that I fell in love with the first time I saw it growing in a garden-tour garden several years ago. Alas, when I studied the patterns of sun and shadow in my rain garden area, I realized that it only got five hours of sun in August, probably not enough for a plant that needs full sun. Instead, I opted to plant Hydrangea paniculata ‘Pinky Winky,’ which is similar in size to ‘Quickfire,’ has beautiful two-tone cream and mauve flowers, and can thrive in a part-sun location. (As the catalog from my local nursery says, “Once you get past the name, this is a very worthwhile addition to a crowded group of plants.”)

I dug the hole for the hydrangea, filled it with water, and let it drain before putting in the plant and backfilling. Then I watered it thoroughly again. The hydrangea will eventually grow to largely fill this rain garden space, but I don’t want weeds covering the ground around it. Once the hydrangea was in place, I planted more of my groundcover geranium ‘Biokovo’ (a plant of which I have an almost infinite supply), putting in divisions around the circumference of the rain garden floor, and adding a few more in the side near the top lip on the upslope edges. These plants will grow toward each other and toward the hydrangea, probably forming a solid ring around it within 2-3 years. I also hope it will grow upward along the sides of the rain garden, stabilizing the soil and maybe even spilling out a bit over the top. As an added bonus, this attractive groundcover sports lovely pink and white flowers in June that will anticipate the colors of the hydrangea blooms.

rain garden with biokovo

We have rain forecast for later today, which will provide a chance to see how well my mini rain garden does in collecting rain from the roof.

15 Comments leave one →
  1. September 3, 2017 3:59 pm

    Jean, those downspout extensions also come in dark brown, which is much easier to “hide”. Good luck with the hydrangea. You’ve done everything possible for success!

    • September 12, 2017 10:16 pm

      Ginny, Thanks for the tip. I don’t know why I bought the white; I guess because the downspouts are white. In addition to the dark brown, they also come in “stone” (close to the color of my house and to my sandy soil0 and in green. I’ll wait to see how much the vegetation grows up to camouflage the extension, but it’s good to know that I have the inexpensive option of switching it out for a less intrusive color.

  2. September 3, 2017 11:53 pm

    I hope your Hydrangea thrives, Jean! It’ll look lovely with Geranium ‘Biokovo’. I grew the latter successfully in my former garden but repeated attempts to grow it in my current garden have failed, which is a pity as it was one of my favorite plants too.

    • September 12, 2017 10:18 pm

      Kris, So far, so good with the hydrangea. We had several inches of rain in the week after I planted it. Since then, I’ve dumped the water from the dehumidifier on it once or twice. Happily, it has not shown any wilting at all, even this afternoon when temperatures got into the upper seventies.

  3. September 4, 2017 2:01 am

    That is so interesting. Here in Ireland I have a giant rain garden! I am trying the opposite and I hope to build a rockery if I can provide enough drainage. We must be kucky as we have loads of hydrangeas, my neighbour calls the “old folks bushes,” but I love them and have taken a few lace cap cuttings this year so I can grow more. Loving the blog 🙂

    • September 12, 2017 10:21 pm

      LOL, it seems appropriate that as I am approaching my 70th birthday, I have planted an “old folks bush.” I think you probably get quite a bit more rain in Ireland than we do here, but your soil must also be different. Maybe those receding glaciers at the end of the last ice age scraped up most of the sand from your part of the world and deposited it on this side of the Atlantic.

  4. September 4, 2017 10:14 am

    Jean, I hope the rain garden works out! Thousands of gallons of rain falls off a roof, so this is an opportunity to put some of it to good use. We also live on a slope so I have several dry stream beds around the house that fill with rain. There is rudbeckia planted in the sunny ones and hosta in the semi-shaded beds. It has worked and created an interesting look to my landscape. K

    • September 12, 2017 10:24 pm

      Kathy, All gardening is a process of trial and error, but I’m hoping this will turn out to be a success rather than an error. The problem here is that the water drains into the sand so quickly. I suppose that’s why we have such luxuriant aquifers and a water export business. (The Poland Spring bottling plant is just a few miles down the road from my house.)

  5. Joanna @ Gingham Gardens permalink
    September 4, 2017 1:45 pm

    It will be fun to see how this fills in. Please post an update.

    • September 12, 2017 10:25 pm

      Joanna, I will definitely post updates next year.

  6. September 11, 2017 12:17 pm

    Hello Jean, the size f the rain garden for the roof area is a lot smaller than I was expecting. If your drive is impermeable, do you have channels either side that support moisture-loving plants. I hope your hydrangea thrives, it’s been given the best start it can!

    • September 12, 2017 10:32 pm

      Sunil, The only impermeable surface on my 1 1/2 acre property is the roof of my house. I live on a dirt road, about one-tenth of a mile from the paved road, and my driveway is gravel. Even my walkways and patio are semi-permeable rather than impermeable.because of the seams between the concrete paving stones and the decorative bands of pea gravel that separate/connect different sections of walkway. This downspout only drains about one-quarter of the roof of my not-very-big house. Then there’s my sandy soil, with sand going down about 40 feet. A few days after I finished the rain garden, we had evening thunder storms with torrential rain. At one point, I looked out to see if rain water was collecting in the rain garden and was happy to see that it was. Two minutes after the rain stopped, I looked out and it had already completely drained!

  7. September 13, 2017 6:18 am

    I am thankful to you because your article is very helpful for me to carry on with my research in the same area. Your quoted examples are very much relevant to my research field. I also want to create a small rain garden on the roof .

    • September 13, 2017 9:28 pm

      Allen, My rain garden isn’t on the roof, but it collects runoff from the roof. I would think putting extra water collection actually on the roof would be a bad idea.


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