Plant of the Month (December) : Pale Spikerush – Eleocharis macrostachya

Pale spikerush (Eleocharis macrostachya) in Mother Nature's Backyard 

 

After four years of drought – and spotty summer rain – our plants are blooming at unusual times.   As we’ve already featured many of our December-blooming plants, we’ve chosen a species that often begins growing in December for our Plant of the Month.

The Spikerushes (genus Eleocharis) are a common component of wetlands throughout the world.  These grass-like plants, members of the Sedge family (Cyperaceae), have rudimentary leaves and understated flowers at the tips of upright stalks.   Nearly all are wetland species and some – like our own Pale spikerush – can even begin growing in shallow water.

Pale spikerush (Eleocharis macrostachya): new growth
 after winter rains.

 

The taxonomy of the Spikerushes presents challenges not uncommon in plants with relatively few relevant characteristics and cosmopolitan (widespread) geographic distributions.    Eleocharis macrostachya grows from Alaska and Northern Canada, as far East as the Great Plains states, and South to Mexico and South America (Argentina, Colombia and Uruguay). 

In California, it’s a common and widespread member of wetland communities from sea level to about 8,000 ft. (2500 m.)  It grows in a variety of wet places including marshes, roadside ditches, and along streambanks, lakeshores and rivers.  It also can be seen in seasonal wetlands, including mountain meadows, vernal pools/marshes and other seasonally flooded areas.

Pale spikerush (Eleocharis macrostachya) in vernal marsh
 (Madrona Marsh Preserve).  Taller plants in back are Tules
 and Cattails.  Note how the spikerush grows around the
 edges of the marsh.

 

Known by the common names of Pale spikerush, Common spikerush,  Creeping spike rush and Wire grass, Eleocharis macrostachya shares many characteristics with Eleocharis palustris; some specimens have been included in this and several other Eleocharis species in the past.   There is widespread morphologic variability within Eleocharis macrostachya, even in California, so future taxonomic revisions shouldn’t surprise us.

 

Pale spikerush (Eleocharis macrostachya) in vernal pool:
 Madrona Marsh Preserve, Torrance CA.

 

Pale spikerush is a rush-like perennial that spreads via rhizomes to form dense mats.  In lowland S. California, seeds germinate – and plants begin to grow – with the winter rains. The under-water stems are hollow; stems become pith-filled on land, giving them added stiffness.   The plants can grow either in shallow standing water or in moist soils, making them useful for seasonally moist areas like rain gardens and infiltration swales.  The plants continue to grow until the dry days of summer, when they become dormant and turn a lovely glossy tan.

Pale spikerush (Eleocharis macrostachya): note stems
 with rudimentary leaves at base.

 

Pale spikerush is 12-18 inches (30-45 cm.) tall.  It can grow as a single stem, as a tuft-like cluster of stems or as a mat-like ‘sod’.  The stems have very rudimentary leaves (thin, red-brown sheaths at the base of the stems) and are smooth and upright (see above).  Stems are pale yellow-green under water, medium green on land.  This is a simple, but pretty wetland perennial.

Pale spikerush (Eleocharis macrostachya) blooming in June:
 Madrona Marsh Preserve, Torrance CA.

 

The flowers of Eleocharis macrostachya grow in purple-brown spikelets at the ends of the stems.  As seen in the photo above, flowering plants are showy, even though individual flowers are rudimentary.  The spikelets are slender and cylindrical, somewhat like a flame on a candle, and contain many small flowers, each encased in a floral scale.  Since the flowers are wind-pollinated, there’s no need for fancy petals to attract animal pollinators.  Instead, the sexual parts are well-situated to ensure pollination (see below).  The seeds are enclosed in a gold-brown achene (capsule with one seed) that drops from the plant when ripe.

Pale spikerush (Eleocharis macrostachya): close-up of spikelet.

 

Pale spikerush is a very adaptable plant.  It will grow in just about any soil, including clays and the sandy, alkali soils along our coast.  It tolerates full sun to fairly shady conditions, with flowering more reliable in full sun.  It does need moist soils in winter/spring and can even tolerate seasonal flooding or shallow standing water, particularly if water levels are allowed to fluctuate through the year (becoming shallower or dry in summer/fall). 

Rain garden at Mother Nature's Backyard.  Pale spikerush
(Eleocharis macrostachya) is indicated by arrow.

 

Pale spikerush is most commonly used as a pond/pool plant or in rain gardens, vegetated (infiltration) swales or bog gardens.  We grow it in our rain garden and as a grass substitute under our Elderberry tree at Mother Nature’s Backyard. It does fine with occasional (monthly or twice-monthly) summer water. When grown in mass (like a turf) it becomes a lovely ‘straw’ groundcover in late summer/fall.  In fact, spikerush straw is harvested in some parts of the world.

Alkali heliotrope (Heliotropium curassavicum)  growing through
a mulch of Pale spikerush (Eleocharis macrostachya)

 

Several points should be emphasized regarding Eleocharis macrostachya.  First, it is a wetland plant that spreads via rhizomes.  In our personal experience, it’s not particularly aggressive in a fairly dry garden.  But if you water frequently – and want to limit its spread – then plant it in a container.  The second issue involves plant-plant interactions.  Some sources note that Pale spikerush may inhibit the growth of other plants.   We’ve not noticed this ourselves and suspect it may be most important when dense Eleocharis ‘turf’ is allowed to dry, uncut, and release chemicals into the soil.

Pale spikerush (Eleocharis macrostachya) straw in summer.

 

That being said, Eleocharis macrostachya is a wonderful native for seasonally moist areas.  It’s great for rain gardens and ponds, stabilizing the soil on banks and slopes.  It is easy care, requiring only the removal of dead stalks in fall.  It provides food and cover, as well as nesting materials, for birds and smaller animals.  In days of old, the stems were used for weaving and dried stems for stuffing pillows and bedding.  Some Native American tribes used the plant as a medicine to induce vomiting. 

We love Eleocharis macrostachya as a reminder of the seasonal wetlands once common in the South Bay.  Spikerushes tie us to the past, providing a sense of place.  Ironically, our rain gardens and seasonal swales have become our region’s wetlands.  They are places where the plants of old continue to thrive, a remnant of the vibrant ecosystems that were once the heart (and kidneys) of our region.



Mixed groundcover with Pale spikerush (Eleocharis macrostachya), Carex pansa and 
Stachys bullata.

 

 

For a gardening information sheet see: http://www.slideshare.net/cvadheim/gardening-sheet-eleocharis-macrostachya

For more pictures of this plant see: http://www.slideshare.net/cvadheim/eleocharis-macrostachya-web-show

For plant information sheets on other native plants see: http://nativeplantscsudh.blogspot.com/p/gallery-of-native-plants_17.html

 

 

We welcome your comments (below).  You can also send your questions to: mothernaturesbackyard10@gmail.com

 

 

 

Preparing for (El Niño?) Winter Rains

 

Sustainable gardening in Southern California means coping with highly variable precipitation. This month, we’re continuing to manage the effects of an epic four-year drought.  And now scientists are cautiously predicting an El Niño winter, with higher than average amounts of rainfall.  Yup, that’s gardening in our capricious mediterranean climate!

The U.S. Weather Service has official precipitation records for the L.A. Civic Center going back to the 1877-78 season (the water year runs from July 1-June 30) [1].  Since then, the average yearly rainfall is 14.93 inches [1, 2].  During the 138 year period, extreme precipitation years (both high and low) have become more common. 

 

 

The graph above shows the number of years below and above the average for two 25-year periods: 1890-1915 and 1990-2015.  One thing is clear: there are more ‘extreme precipitation’ years (both below and above average) in the current period.   The last 25 years had 10 years with a deficit of at least 5 inches.  This compares to 6 such years in the earlier period.  But there were also 6 years with 5 or more inches over the average (compared to two from 1890-1915).  So we need to prepare not only for more ‘drought’ years, but also for more ‘wet’ ones.

We gave you some tips for surviving the drought (http://mother-natures-backyard.blogspot.com/2015/07/surviving-drought.html) and summer planning last month: http://mother-natures-backyard.blogspot.com/2015/07/summer-time-for-garden-planning.html.   This month we suggest ways to prepare for this winter’s rains - El Niño or not. 

First, a word of caution. Mother Nature’s Backyard is situated in the flat lowlands of the Los Angeles Basin.  Our advice is most applicable to gardeners in similar areas. If you live in the foothills, and particularly if you live along a creek, in areas below recent burns, or those prone to landslides, you may need to take additional precautions.  Consult your local municipality for advice on preparing for an El Niño winter.  Recent ocean temperatures indicate that this may be a very wet winter.  Prepare now if you live in a flood-prone area!

The rest of us still have several months to make our gardens both more water-wise and more El Niño proof.   Some of the suggestions below may not be applicable.  But we hope you’ll adapt some for use in your garden – and get moving on making them happen.  The time is now to prepare for the winter rains.

1.   Consider decreasing the area covered with impervious materials. Traditional walkways, driveways, concrete or mortared patios all are impervious surfaces. Water runs off them and, very often, into the storm drains and out to the ocean.   That’s one reason why urban areas like the Los Angeles basin need such extensive storm drain systems.

El Niño years can be tricky.  Whether they bring deluges or persistent showers, excess water can become a challenge for local gardens.  Fortunately, you can take several steps to prevent/decrease the effects of running or standing water in your garden. 

One strategy is to increase the percentage of the yard that can infiltrate rain water.  This allows more water to infiltrate in place, rather than aggregate in ponds or rivulets.  We discuss several infiltration options below (see suggestions 2 & 3).  Another idea is to simply convert impermeable surfaces to permeable ones.  This helps control excess rain water and also increases the amount of irrigation water available to plants (by decreasing summer run-off).

Permeable walkways in Mother Nature's Backyard

 

There are many ways to make walkways, patios and driveways more permeable (see the links below).  Some, like replacing your driveway with permeable paving materials, require more time, skill and money.  Others, like converting an old concrete patio or walkway into something more pervious, can be done quite economically, if you’re able to do most of the work yourself.  For ideas on permeable surfaces see:

·         http://mother-natures-backyard.blogspot.com/2013/06/harvesting-rain-permeable-paths-patios.html.

·        http://www.slideshare.net/cvadheim/permeable-surfaces

 

2.   Use the rainwater that falls on your roof.  Your roof is a large rain collector. Does the water from your roof end up in the storm drains?  Does it make a muddy mess around your house, threatening the health of your foundation? If so, now is the time to install gutters and harvest rain from your roof.  

A rain chain is another way to direct water from a gutter

The advantage of gutters is that they let you direct the water collected by your roof. You can then store the water (see #4, below) or direct it to places where it can be infiltrated into the ground (#3, below).   For more information on rain gutters see: http://mother-natures-backyard.blogspot.com/2013/02/harvesting-rain-gutters-downspouts-and.html.  

3.   Infiltrate more water into the ground using a rain garden, dry well or dry swale. Water from impermeable surfaces must go somewhere. In the past, most of it has ended up in the ocean.  But each year, more California gardeners are installing simple infiltration ‘devices’ in their gardens. 

While getting rid of one problem (excess runoff), these devices also solve another: providing deep water resources for trees and shrubs.   They allow water to infiltrate into the ground, replenishing the ground water.  Trees, shrubs and other long-rooted plants can then access this ground water well into summer.

If you have an area where rain water puddles, you may want to consider a simple infiltration device like a dry well.  These take little space, are relatively easy to install, and often solve the puddling issue admirably.  They can be used in unplanted areas, making them a good option for patios and utility areas covered in gravel mulch.   See the links below for more information.

Rain garden - Mother Nature's Backyard garden

 

Rain gardens and infiltration swales are the perfect complement to rain gutters, infiltrating the water from a roof. While no two rain gardens or dry swales are the same, they all slow or store water briefly, allowing it to percolate into the ground.   They can be planted or not; they can be disguised as a natural-looking dry creek. Some are used as seating or play areas in the dry season.  And they allow you to use plants that like a little extra winter water, even if the rest of your garden is quite water-wise. 

Rain gardens, dry wells and dry (infiltration) swales are easy to incorporate when you are installing a new garden (or re-doing an old one).    Like all hardscape features, they’re easiest to install before a garden is planted.  If you’re removing your lawn, now is a good time to consider whether a dry well, rain garden or dry swale is right for your garden. Here are some good resources:

·        http://mother-natures-backyard.blogspot.com/2013/03/harvesting-rain-rain-gardens-and.html.

·        http://www.slideshare.net/cvadheim/infiltration-gardens-2015

·        Plants for Rain Gardens and Vegetated Swales: http://www.slideshare.net/cvadheim/rain-gardensswales

4.   Consider storing some water.  People in dry climates around the world store rainwater for use in dry periods.  The regulations on rain water collection/storage are changing, so check your local municipality to learn what is legal.  Nearly all S. California municipalities permit you to store water in rain barrels, to be used for watering your garden (not for drinking).

As rain water storage gains popularity, more options are available locally and on-line. Fifty gallon plastic rain barrels are sold at many hardware and do-it-yourself stores.   Some water companies give them away for free or at low cost.   And larger storage containers are also becoming more common. For more on rain water storage see:  http://mother-natures-backyard.blogspot.com/2013/06/harvesting-rainwater-rain-barrels.html

As water becomes more scarce (and costly) it’s silly to not take full advantage of the rain that falls on your property. California law is now clear – you own that water!  Don’t let it slip away.   Act now to use your clean, free rain water this winter.

5.   Use the ‘high’ and ‘low’ spots in the garden to best advantage.  Sandy soils dry out quickly in summer; clay soils tend to hold water, creating wet spots in winter.    Most gardens have areas that are ‘high and dry’ and others that are low and moist.  If not, it’s relatively easy to create a bit of garden topography with low berms (artful mounds) and shallow swales. 

Whether your soil drains quickly, slowly, or somewhere in between, creating modest garden topography has several advantages.  First, a planted berm is often an excellent way screen short, unsightly views (for example to block views of parked vehicles).  Berms and swales can also be used to direct and infiltrate rain water.  And they add interest to a flat garden.

Another benefit of berms and swales is that they allow you to grow plants with water requirements slightly different from those available in the rest of your garden.  For example, plants that hate wet feet can be grown at the top of a berm (driest place). Plants that like a little extra water often do well at the bottom of a slope or swale.  For more on creating garden topography see: http://mother-natures-backyard.blogspot.com/2012/12/getting-to-know-your-gardens-soil.html.

 

Fresh organic mulch: Garden of Dreams, CSU Dominguez Hills

6.   Consider replenishing mulch a little early this year. Newly laid mulch is  more vulnerable to washing away.  If you use mulch, consider doing your fall mulching in late summer or early fall.  That will allow the mulch to compact a bit before the winter rains.  For more on mulches see: http://mother-natures-backyard.blogspot.com/2012/07/understanding-mulches_23.html

7.   Use the weather forecast to plan fall pruning.  Fall pruning is best done after the fall heat waves but before the winter rains.  Predicting the best time to prune can be a challenge.  Consult the long term weather forecast when scheduling fall pruning.  Don’t forget to consider the birds and other creatures that rely on your garden for food.  For more on the topic of fall pruning see: http://mother-natures-backyard.blogspot.com/2014/11/maintaining-your-new-california-garden_15.html

Fall pruning - Mother Nature's Backyard garden

8.   Choose trees, shrubs and vines that can take both drought and excess rain. Global climate change makes planning for the future a bit more challenging.  We’re already seeing some effects: hotter temperatures overall; more temperature and precipitation extremes; changes in the timing of the seasons.  The recent drought is just a taste of things to come.

Trees, vines and large shrubs are an excellent way to provide shade. In fact, all local gardeners should be planting now for future shade.  With planning and proper care, large shade plants can live for many years.  But choosing the best adapted plants is something we’re just beginning to grapple with. 

In Southern California, our best choices will need to withstand both the periodic droughts and periods of greater precipitation. Only certain plants are so adapted. California native trees and shrubs are better candidates than those from the tropics or other regions with plenty of precipitation.  But what native trees and shrubs will be able to take both the heat and the precipitation extremes?  We have some ideas and will discuss that topic next month (September, 2015).

 

Planting Mother Nature's Backyard garden

9.   Take advantage of winter rains for planting.  Winter is the easiest time to plant in lowland Southern California.  Soils are well-moistened and the temperatures cooler.  That’s why California native gardens are traditionally planted in late fall or winter.

Winter is not only the easiest time to plant, but it’s also the best for plant health.  California native plants are adapted to our seasonal weather patterns.  Many are dormant (or at least slow growing) by late summer or fall; they are primed to grow with the winter/spring rains.  Plant them in late fall/winter and they will establish themselves right on schedule. 

But plant California native plants in summer and they’ll be ‘seasonally confused’; the heat says ‘it’s time to go dormant’ while the irrigation water says ‘it’s time to grow’.  In fact, summer planting is difficult not only for the plants, but also for the gardener.   Planting with the rains is yet another example of working with Mother Nature.  Gardening elders have learned – often through painful experience - that working with Mother Nature is better than trying to work against her!

An El Niño year can be an excellent opportunity to start a new garden – or plant trees and large shrubs.  So do your summer planning now.  Figure out what plants you need.  Plan to buy required plants at the fall plant sales, and plant them with the winter rains.

Rainy day - Mother Nature's Backyard garden

10. Enjoy today’s weather, whatever it may be.  The news on climate change can be downright depressing.  The best antidote is to sit in your garden.  Enjoy the hot, dry days of late summer.  Watch the abundant life that enlivens California gardens this time of year.  Enjoy the balmy evenings – and vow to plant more silvery-colored shrubs to enhance your twilight garden.  

Look forward to the cool rains.  Sit out in your covered patio and smell the rain.  Listen to the sounds of a rainy day in your garden.  Watch the birds and other creatures – what are they doing on a rainy day?  Put your potted plants out to benefit from the good, pure water.

Those of us in California are blessed with a wonderful climate, with seasons that promise beauty and interest every month of the year (http://mother-natures-backyard.blogspot.com/2014/09/seasons-in-southern-california-garden.html).  But where ever you may garden, there’s something wonderful in your garden right now.  So, enjoy today’s weather – whatever it may be.

___________________

1. http://www.laalmanac.com/weather/we13.htm
2. http://www.wunderground.com/blog/weatherhistorian/show.html

 

 

We welcome your comments (below).  You can also send your gardening questions to: mothernaturesbackyard10@gmail.com

Harvesting Rain: Rain Gardens and Vegetated Swales

Rain garden in Mother Nature's Backyard

Your home roof is likely the largest impervious surface in your garden.   Last month (February 2013) we talked about gutters, downspouts and rain chains which can be used to collect and direct roof water.  This month and next we consider methods for infiltrating the water from impervious surfaces into the ground.

 

Why infiltrate rainwater?    Rainwater is clean, free water. As our planet heats up, methods to capture and use rainwater become increasingly important.  Some of the benefits of keeping rainwater in your own garden include:

1. Saving money – rain water is free water
2. Conserving a valuable and increasingly scarce resource – water
3. Helping replenish the ground water
4. Providing habitat for insects and birds
5. Providing a place to plant interesting stream and pond-side plants
6. Teaching children the values of conservation and water-wise gardening
7. Deep watering your garden’s trees and shrubs (in winter/spring in our area)

 

One simple but effective infiltration tool is the rain garden or vegetated swale.  Rain gardens/swales capture water that would otherwise run into the storm drains - and allow it to percolate into the ground.   They make sense for many home gardens and are becoming increasingly popular throughout the world.

What is a rain garden?  A rain garden is a small garden where runoff from impervious surfaces (roof, driveway, patio, walkway) is directed. Rain gardens are like leaky ponds – they hold rainwater just long enough for it to soak into the soil.     Because they only have standing water right after a rainstorm, you don’t have to worry about mosquitoes and other problems associated with standing water.  Rain gardens are often planted with wetland plants that help hold the soil and make the garden beautiful and life-friendly.

 

What do rain gardens look like?  

 

 

Almost all rain gardens have these common features:

 

• An intake area (often a downspout, pipe, channel, etc.)
• A shallow depression (like a shallow pond) to hold water briefly
• A layer of gravel or rocks to help the water to soak in
• Wetland plants that take occasional flooding & hold the soil
• May have: an infiltrator device - to help water soak in faster

 

Rain gardens can be any shape – from round like a pond to linear like a dry stream bed (these are called vegetated swales).   The size of the rain garden is based on the amount of water that needs to soak in.  The shape depends on your needs and tastes – and the available area.

Rain garden designs often have a regional ‘look’.  For example, rain gardens in places with summer rain (for example, Pennsylvania) are often kidney-shaped flower gardens located in low areas of the lawn.  But there’s no reason that all rain gardens need follow this design.  In summer-dry regions like Southern California, rain gardens can be completely dry from late April through October.  In these regions, a rain garden can serve a dual-purpose - functioning as a water infiltrator in winter and something else during the dry season. 

A little creativity can suggest ways to make your home rain garden meet your needs and tastes.  Here are just a few ideas of what a Southern California rain garden might look like:

• An unmowed ‘lawn’ in a slight depression
• A concrete planter featuring plants that can survive winter flooding
• A summer pathway with gravel and pavers
• A summer seating area, often featuring pavers or stone slabs set in gravel
• A ‘dry creek bed’ planted local native streamside plants
• A Japanese (Zen Garden) or Mediterranean style gravel garden (maintained as a formal gravel garden during the dry season)

 

As rain gardens become more common, landscape architects and homeowners alike are developing more creative and functional designs.   We suggest you search the internet for designs that inspire and work well with your lifestyle, climate and garden.

Does my rain garden need to be planted?  No, in fact some very successful rain gardens contain no plants at all.  However, there are several good reasons to select a planted rain garden.  First, the plants serve as habitat for birds, butterflies and other insects.  They may even provide food for your family.  So, a planted rain garden is usually more life-friendly than one with no plants.

A second reason to plant your rain garden is that it will be cooler.  In our climate, planted areas play an important role in keeping gardens cooler during the hot, dry summer.  If you live in a mediterranean climate, this can be an important advantage.

 

Another reason to include plants in a rain garden is that their roots help rainwater infiltrate more quickly.  Roots help keep the soil texture open, allowing water to infiltrate better.  This is obviously an advantage in a rain garden.

 

Finally, a rain garden provides the ideal place to grow plants that like a little extra  water.  These include some wonderful native pond-side and stream bank plants.  Planting a rain garden with these plants – and using rainwater to water them during the rainy season – allows you to enjoy these beautiful plants.

 

Building a Rain Garden

 

Check your soil drainage to determine if your soil is suitable.   Dig a 1x1 foot hole and fill it with water.  Let the water drain out completely.  Fill the hole again and check after 1 hour.  If the water drains at least 1-2 inches per hour your soil is suitable for a rain garden.

Choosing a location is key to designing a successful rain garden.  The location should either be near the impervious surface(s) it drains or in a place where water can be easily diverted to it.   Ideally, a rain garden that infiltrates water from a large surface (such as a roof) should be at least 8-10 ft. rom any structures or utility lines and 3 ft. rom sidewalks and walkways.  Rain gardens that drain patios or walkways are usually located fairly close to the surface they drain – usually 1-2 feet away.   In Mother Nature’s Backyard, the water from half of our small roof runs down our rain chain, into an infiltration pot and then directly into our rain garden. Ideally, the rain garden would be located a bit further from the structure.  However, the small amount of drainage area, coupled with the depth of our rain garden, made our location feasible.

 

Rainwater from the north half of the roof flows down the
 rain chain into a  large pot and then into the rain garden

 

 

Determining the size and depth of the rain garden is fairly easy. First you need to determine how much rain falls per hour during a good rainstorm.  Then you convert this amount to cubic feet.  In our area of Southern California, we rarely get sustained rainfall that exceeds ¾ inch per hour.  Therefore a rain garden in our area should be able to contain at least 3/4 inch (.0625 cubic ft.) of rain that falls on the impervious drainage surface. This is probably the least amount of rain fall you should plan for – even in the desert, a rainstorm can drop an inch or more of rain in an hour.   

If you live in an area with heavier rainfall, you’ll need to increase your estimate accordingly: 1 inch per hour = 0.083 cubic feet; 1.25 inches = 0.104 cubic feet; 1.5 inches = 0.125 cubic feet; 1.75 inches = 0.146 cubic feet.    To convert any rainfall per hour to cubic feet simply multiply the rainfall amount by 144 and divide this number by 1728. 

 

Next determine the area of the impervious drainage surface by multiplying the length of the surface times its width.  For example, a 20 by 30 ft. roof has an area of 600 square feet.  Multiply this by the cubic feet of rainfall (0.0625 in our area) to get the total cubic feet of water from the drainage area (600 x 0.0625=37.5 cubic feet).    This is the amount of water your rain garden will need to contain before it infiltrates into the ground.

Most home rain gardens are 1-3 feet deep (with most of the depth filled with gravel or dirt – see below).  Decide on a depth and divide the cubic feet of water (37.5 cubic feet) by the depth (2 feet) to get the surface area of your rain garden (37.5 / 2 ft. = 18.75 square feet).   In this example, an oblong rain garden that is 3 ft. wide by 6 ½ feet long and 2 feet deep will do the trick.   It’s prudent to make your rain garden a little larger than the calculated size and to also plan an overflow area in case of heavy rainfall.  Mother Nature is full of surprises these days!

 

 

 

The shape of the rain garden may be dictated by the site or designed by you.  Gardeners often find that rounded shapes are most pleasing; but the design depends on your needs and the design of your home and garden.  You can easily lay out the basic shape for your rain garden using a garden hose.  As long as the size is adequate, the shape of the rain garden is up to you.   Our rain garden is oblong with rounded edges and a dry-stone wall on the walkway side to provide stability and a decorative appearance.

  

 

Digging the rain garden can usually be done with a shovel and a little effort.  We had a little mechanical help, but did much of the digging with picks and shovels – even in our heavy, debris-filled soil. The excavated area should have gently sloping edges.   Pile the excavated soil around the edges to create a small berm around the rain garden.    You can see our fully excavated rain garden above.  Because our area in Mother Nature’s Backyard is limited, our rain garden is fairly deep - about 3 ½ feet at its deepest point.  Because the rain garden is filled with gravel and a layer soil, only the only the top part is visible (see photo below).

 

Rain garden is filled with gravel and smooth.  Next a 6 inch layer
of soil was placed over the gravel layer.

 

 

Fill the bottom of the rain garden with at least 6-12 inches of gravel. This will help the water to infiltrate better.   If your rain garden is deeper than 2 feet you can use more gravel.   The surface of the gravel layer should be at least 8-10 inches below the level of the surrounding soil.  Rake the gravel to make it level.

Cover the gravel with 4-6 inches of garden soil (use the excavated soil).  This will be sufficient for the bottom plants, many of which will grow through the gravel layer and into the soil beneath the rain garden.

Smooth/compact the berm to create gently sloping edges.

Plant the rain garden with appropriate plants (see below).

Mulch around the plants with an appropriate mulch.  Depending on the plants, this may be an organic or inorganic mulch (see our July 2012 posting on ‘Garden Mulches’).   In Mother Nature’s Backyard we used chunks of sandstone left over from the stone pathways to create a color-coordinated inorganic mulch at the bottom of the rain garden.  The plants on the berm are lightly mulched with wood chips until they grow to cover the area.

 

Choosing Plants for Rain Gardens

 If you live in Southern California,  we suggest choosing California native plants for their beauty, life-friendliness and suitability. Otherwise, consider using plants native to your own local area.   You will need to choose two types of plants:

Plants for the bottom of the rain garden.  These plants will be briefly flooded after a rainstorm and the ground will be seasonally moist.   You need to choose plants that normally grow along streams or around ponds and lakes (riparian plants).  These plants are often short (1-3 feet) and grass-like.  Some typical examples are rushes, spike rushes, and some annuals and perennials like annual Monkeyflowers (Mimulus) and even Miner’s Lettuce (see February 2013 Plant  of the Month).

Plants for the upper sides and berm.  These are plants that like damp soil in winter and spring. This area will likely be too damp for the most water-wise local plants (like local native Salvias), particularly if your soil drains slowly.  However, there are many lovely plants to choose from.  These range in size from grasses and sedges to large shrubs and even trees. 

A list of California native plants appropriate for the bottom and sides of rain gardens is available at: http://www.slideshare.net/cvadheim/south-bay-native-plants-rain-gardens-swales-213

A talk on rain gardens & vegetated swales (complete with discussion of some appropriate plants: http://www.slideshare.net/cvadheim/infiltration-gardens-2015

  

Additional Resources on Rain Gardens

http://raingardens.spawnusa.org/rainwater-harvesting-principles.html

Brad Lancaster's Rainwater Harvesting for Drylands and Beyond, Volumes 1 & 2

http://www-csgc.ucsd.edu/BOOKSTORE/Resources/GS3%20Rain%20Gardens_8-10-09.pdf

LA Rain Gardens - http://www.laraingardens.org/  

http://www.landscapedesignerlosangeles.com/Rain_Gardens_and_Bio-Retention.html

 

You can also e-mail your Water Zone questions to: mothernaturesbackyard10@gmail.com