Experiments With Gravel Mulch

Yucca filamentosa ‘Colorguard’ has appeared from under our newly installed gravel mulch.

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Most of the mulches we use are organic and improve the soil as they decay.  Shredded bark or leaves, pine straw, straw, newsprint or brown paper all have their uses.

When we consider inorganic mulches, there are definite benefits along with some obvious deficits.  Inorganic mulch won’t improve soil texture or fertility.  But neither will it harbor fungal disease, come pre-contaminated with weed seeds, provide a nesting site for ants or decay in just a few months.

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New terraces are planted to help control erosion, and mulched with pea gravel (spring 2017).

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I was first drawn to pea gravel mulch as we began to try to control erosion and cultivate the steep slopes of our back garden.    But I was also digging some gravel into the back-fill and planting hole when we installed new shrubs and perennials, to try to thwart the voles who would otherwise devour their tasty root balls.  Finishing the job with a nice mulch of gravel felt appropriate as a further deterrent to rodents.

Pea gravel definitely helps both with erosion control and rodent control.  But it also ‘disappeared’ into the soil on rainy days, after a while, and got covered with leaf litter and other organic matter over time.  I find myself renewing the pea gravel in spots after a while.

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“Soil security”

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Gravel mulch serves to help conserve soil moisture, just like every other sort of mulch.  It shades the soil, shelters root systems, absorbs the shock of falling rain and holds soil in place.

Additionally, gravel reflects sunlight and heat back up into the plants above it, helping to dry the plants more quickly after a rain and thereby deter fungal disease.  Gravel mulch also provides a dry barrier between moist soil and dry plant, preventing crown rot.

Soil doesn’t splash up onto lower leaves and branches, and the gravel perhaps makes it a little harder for invertebrates to travel up and back between soil and delicious plant above.

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Gravel mulch is used most commonly in rock gardens, where many drought tolerant and alpine plants are featured.  Some plants wouldn’t live long with a moist organic mulch, but manage just fine with gravel mulch that protects their crown.  Gravel is coming into vogue again as a fashionable and useful mulch for perennial gardens, too.  I have been reading about perennial and succulent  gardens grown under several inches of pea gravel in various garden magazines.

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Even a thin gravel mulch has helped conserve moisture around these newly planted perennials.

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I also recently enjoyed listening to a presentation by Joseph Tychonievich at the Williamsburg Botanical Garden where he presented his new book, Rock Gardening:  Reimagining a Classic Style.  Joseph inspired me to move ahead with my vision to incorporate more areas of gravel mulch in our sunny perennial beds in the upper garden.

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I use fine gravel as a mulch in potted arrangements, too.

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This area is gently sloping, and erosion isn’t as much of a pressing concern as in the lower gardens.  The entire area was left under several inches of freshly ground hardwood mulch in 2013, as the arborists who cleaned up our fallen trees ground up leaves and branches and simply left it all in place.

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Fresh compost piled on top of existing mulch allows me to plant in this area in 2013, right after the trees came down, without digging into the clay. A light covering of wood chips from the forest floor mulches the planting .

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As that has decomposed, I’ve renewed the mulch with bagged hardwood and Cypress mulch from the local hardware store.  It smells pleasant, and Cypress helps to repel insects.  It has an ecological downside, though as mature trees are cut for mulch.

The soil in much of this area still consists of thick, hard clay, despite my best efforts to dig in compost and improve its texture.  There may be a few inches of good compost on top of the clay, but the clay still holds heavy rainfall and keeps parts of the garden far too wet, especially in winter.

I am beginning to understand that a gravel mulch will promote better growth and vigor in most of the plants we are trying to establish, particularly the Iris and Mediterranean herbs.

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Recently,  I decided to experiment with a much larger gravel mulch in one of the beds that needed some TLC.  I lost several perennials here over winter, and so had quite a bit of bare ground.

On our shopping trip, my partner noticed this beautiful blue green rock quarried somewhere in Virginia.  We decided on the spot to give it a try, and I am very pleased with the results thus far.  Not only is this gravel not going to shift around on a rainy day, but I don’t believe it will sink down into the soil anytime soon, either.

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This three year old Siberian Iris bloomed for the first time this spring, and I hope the new gravel mulch will help it grow more vigorously in future.

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Now, please keep in mind that gravel is the heaviest mulch you can choose, and moving it around and spreading it takes both strength and commitment.  If I had the luxury of ordering up a truckload of it and hiring a crew to spread it for me, that would be a lovely thing.  But I don’t.

Rather, I’m buying it a couple of bags at a time and spreading it by hand.  It is going to take most of the summer to mulch this whole area working with just a few square feet each week.  But I am already seeing the benefit this mulch brings to our plants.

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This is a single bag of gravel spread around our new Monarda.  It will take a few more bags to finish this area….

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I bought three plugs of Yucca filamentosa ‘Color Guard’ about four years ago, as we were first planting this bed.  I wanted them to make a large focal point to anchor the area and planted them in a broad triangle.  Well, let’s just say that I expected them to grow much faster and they have largely gotten lost between larger and floppier perennials.  In fact, one of the three was struggling so much that I dug it up in late winter and planted it into a pot in full sun, hoping to give it a better chance to grow.

Never mind that I kept digging it up every month or so, checking to see if there was any visible growth, and replanting it again with the confirmation of a fresh root or tiny shoot.  That is a sad tale, and I ended up filling the pot with first one plant, and then another, simply to have something to look at besides the empty pot.  I ticked this off as a failed plant and moved on.

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Maybe if I put a fresh gravel mulch in this pot, the Yucca would finally grow?

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But not so fast!  Something of that Yucca was left alive in the original bed.  And finally, a month after I mulched over the area with the new Virginia gravel, look at what has emerged!  Plants really really want to live, and sometimes we just need to improve conditions for them and get out of the way to give them a chance!

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This newly planted Lavender was struggling with our weather extremes, but has improved under the gravel mulch this month.

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Our friends at our local garden center have a running joke that we always buy gravel or compost, if nothing else, and are their best customers for pea gravel. Gravel has made gardening in this difficult site possible.

If you happen to be in the neighborhood, and want to visit with me and bring a little gift, a fresh bag of gravel is always in style.   I’ll be so happy to see you, will show you around the garden and offer you a few divisions of something nice to take away with you.

And I might even let you help spread the gravel while we’re at it!

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Woodland Gnome 2018

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Fabulous Friday: Rain and Lizards

Hosta in (soggy) bloom

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Our garden is thoroughly watered, I’m happy to share!  And it’s unlikely that any of my gardening friends will be spending chunks of their weekend with a hose in their hand watering after the several inches of rain that we’ve had this week.

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Zantedeschia ‘Memories’

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In fact, the sound of pouring rain roused me well before sunrise this morning.  Downpours have come and gone today, interspersed with glimpses of blue sky and brilliant sunshine.

I appreciate the rain, of course; but am well aware of the flash flooding many have to deal with this week.  It has snarled the local airport with delays as the runway and access roads flooded early this morning.  Local roads flooded out again, and the chocolate milk brown James River is churning very high against its banks.  It is a good day to stay at home!

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Colocasia ‘Coffee Cups’ after this morning’s rain

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Plants hate too much rain, and may perish from their roots up when the soil stays saturated for very long.  I’ve emptied saucers under a few of our pots twice already today, and know I should do the tour and check them all again this evening.

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Artemisia prefers dry conditions. I have potted this one up from its nursery pot into a small ceramic pot just until I can prepare its new place in the garden. 

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All of the small creatures must cope with too much rain, as well.  While there is plenty of fresh water to drink, there is also the small matter of flooding in the nooks and crannies where they generally hide.

We came home mid-day to find our resident lizards enjoying their privacy, sunning themselves on our side porch.  One after another scampered away for cover as we approached.  They know us, and that we bring them no harm.  The boldest held her place on the step making eye contact as I greeted her.  She didn’t scamper into the vines until my shoe touched her step.

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These small lizards are known as skinks.

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Lizards crave warmth and laze about on all of the hardscapes around the house and garden.  Since they gladly eat up insects, spiders, slugs and worms wherever they can find them, I am quite happy to see them hanging around our potted plants.  We have an understanding, as these little guys are quite harmless.  Our cat is in on the bargain and watches them closely, but leaves the lizzies strictly alone.

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It is challenging to plant for the weather and our ever variable ‘climate.’  Those of us who planted drought tolerant perennials, like lavenders, Yucca, and other succulents are watching them try to cope with the saturated soil.  Sometimes herbs will get moldy or turn to mush in our steamy wet spells in summer.

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Spanish lavender wants great drainage and bright sun to thrive.

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That is why it is smart to consider drainage when planting them in the first place.  Plant a bit high, on a bit of a mound, and incorporate sharp sand or small gravel into the surrounding soil to improve drainage.  Mulch with grit, crushed oyster shells or gravel to keep soil and pathogens from splashing up onto their lower leaves in heavy rain.

Sun reflecting off of the gravel mulch will also help dry the plant’s inner foliage more quickly.

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A tiny dragonfly happily hovered around the pots on the patio during a break in the rain this afternoon.

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On the other hand, we have plenty of plants just loving the reliably moist soil.  The Caladiums and Colocasias like even moisture, though even they may rot if the soil stays too wet too long.  When the weather turns dry, these want watering most days to keep them growing happily.

They have a system:  Their large leaves, covered with tiny openings called stomata, allow water transported up from their roots to evaporate into the surrounding air.  So long as their leaves are growing and working in the sunlight, their roots can pump large amounts of water out of the soil and into the air.  Trees do this on an industrial scale!

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Caladium ‘Carolyn Wharton’ and Colocasia ‘Coffee Cups’ both enjoy moist soil.

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The smaller or more protected a plant’s leaves, the less water they will release from soil to atmosphere, and the better they tolerate drought.

It is smart to learn about a plant’s tolerance for wet soil and humidity just as we learn about its needs for sunlight, warmth, PH, and trace minerals in the surrounding soil.  That way, we can give them the conditions they need and keep them growing.

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Succulents with thick, waxy leaves release very little water into the air. They are built for hot, dry conditions and may rot of their soil remains saturated for too long.

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A plant with particular needs, or one that doesn’t thrive in local conditions may still be grown well in a pot.  And of course, pots can be set back under the eaves when the skies open and a downpour comes.

And believe me, our little lizards and toads find lodging in the pots sometimes.  Somehow, it seems to work out pretty well, no matter what strangeness the summer brings.

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“Breathe deep…
The rain falls but a moment,
and in a moment, gives life to another day.”
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Laurence Overmire

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Woodland Gnome 2018
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Fabulous Friday:  Happiness is Contagious. 
Let’s infect one another!

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Caladium ‘Peppermint’ left, and C. ‘Berries and Burgundy’ above and right

Soil Security

Saxifraga stolonifera, Strawberry Begonia

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Gardens offer endless surprises and seemingly endless challenges.  One hopes to discover most of the challenges in the first year or two.  Better to address them right off and be done with it, right?  But that’s not how this business works…. things change….

Ours is a very steep property.  Our bit of James City County spreads across ridges and ravines.  We happen to live and garden on the slope of a ravine.  Water drains down across the yard to a creek running through the ravine, which flows to a pond and then out to College Creek.   Managing all of that water during a heavy rain remains a challenge for us.

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This area suffers serious erosion in heavy rain, and is frequented by voles.  It is hard to get anything much to grow here.  We have just added the stones to offer some protection and planted a dozen seedling Hellebores to help hold the bank.

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Our county’s division of  storm water management staff advise:  “Plant more plants!”  I take that advice to heart, regularly, and have struck up a working relationship with one of the staffers.  They work with the local Master Gardeners to help homeowners design rain gardens to catch some of the run-off after a heavy rain, and offer grants for those who install them.

I like that proactive, cooperative approach.  This spring, I’ve done a bit of reading about how to construct a rain garden.  And one of the first things I realized is that steeply sloping land isn’t a very good place to site one, unless you are prepared for a major project of earth moving and engineering to construct a berm on the down slope side.

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This was our steep, eroding slope before our work began this spring.

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As I thought about rain gardens, and walked our property looking for a place to catch run off and use it in a new planting bed, my partner pointed out a new erosion problem on the very shaded and inaccessible slope beside and below our driveway.

This is an area we’ve largely neglected over the years.  Towering, mature Ligustrum shrubs cast deep shade across this slope.  Their leaves drop here year round, and the ground has been covered in a tangle of Vinca vines and wild growth.  Where there is bare earth, it has been covered with fallen leaves. I planted  some Mahonia and Hydrangea in this area when we first took over the garden, and they have expanded, but never bloomed.

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Daffodils have replaced Caladiums here at the base of our driveway, where a great deal of water runs off when it rains.  An Autumn fern has thrived here for five years or more, and I decided to expand the planting last summer.

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But last summer, I began clearing some of this strip, nearer to the drive, and planted it in Caladiums, Zantedeschia, Ajuga, Oxalis, some transplanted Liriope and a few ferns.  We enjoyed it enough that when we dug the Caladiums in October I planted Daffodils and Arum in their place.

Below this planted area, we noticed a new area of erosion a few weeks ago.  Storm water had found its way into a vole tunnel, and a whole piece of the bank had collapsed.  There was a gorge, partially filled with leaves and other debris.  Finding that bit of erosion sealed the deal that we would invest our time, energy, and gardening dollars in fixing this neglected, and now crumbling, bit of the garden.

Too steep for a single ‘rain garden,’ we decided to create several terraces to catch and slow the flow of water down the slope, directing the run-off from one planted area to another.  We found several Rhododendron shrubs to anchor each terrace, and planted the first right into that nasty gorge to stabilize it.  We found some sturdy trapezoidal concrete blocks for building the terraces.  They fit together snugly to make a secure wall.  We installed the first ones below that Rhododendron to hold it in place.

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The first Rhododendron we planted to stabilize a gorge caused by erosion over a vole tunnel. We planted in the hole and stabilized the area with two concrete blocks.

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We trimmed up the lowest Ligustrum branches to let in light and make the area more accessible and raked back the leaves and debris.  Then, we studied the area for several days to decide where to place our blocks to form natural terraces.

After building the terraces, and planting three more of the shrubs, I began filling each terrace with plants.   I selected a variety of perennials which will thrive in shade, tolerate a lot of moisture, hold and cover the soil by spreading, put down extensive root systems, and stop voles with their poisonous roots. Oh, and did I mention they also must repel deer?

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The terraces before today’s torrential rain.

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Remember our mantra:  “Plant more plants!”  It was going to take a lot of plants to fill these spaces.  Luckily, we have a pretty steady supply now of a few perennials which fill these criteria.  They are ours to dig, divide, and transplant as needed.

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Divisions of Strawberry Begonia transplanted from another part of our garden. Each division will send out numerous stems, with a tiny plant growing at the tip of each.  They will form a thick mat over time. 

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I was able to transplant Hellebore seedlings, Ajuga and Saxifraga stolonifera in nearly unlimited quantities from other parts of the garden.  The Hellebores have  poisonous roots, and so I planted them around each of the Rhododendrons to protect their roots from curious voles.  I also planted them below the lowest row of blocks to form an additional vegetative barrier for any run-off.

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This Rhododendron is ringed with seedling Hellebores.

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I purchased holly ferns, Japanese painted ferns and Autumn Brilliance fern.  Although the Japanese painted ferns aren’t evergreen, they spread wonderfully and give about 7 months of presence here.  I also purchased some little 2″ Columbine and Heuchera and a couple of quart sized Tiarella .

I prefer to buy the smallest pots of perennials I can find to  minimize the size of the holes we must dig.  Living on a slope, we dig as little as possible.

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Tiarella is a shade loving native perennial which runs and spreads over time. It blooms each spring, feeding hungry pollinators early in the season. It resembles Heuchera, but proves more deer resistant.

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Heuchera is the only perennial in our palette for this new bed which may be grazed from time to time.  I am willing to take the chance for its beautiful foliage.  The rest of these plants have already proven themselves in our garden and I have confidence in using them here.  They are tough and thrive in our climate and soil.

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Heuchera ‘Melting Fire’ and Athyrium niponicum ‘Pictum’ anchor the end of this terrace. I will add Caladiums next month when the weather is settled.

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And this was surprisingly good soil!  While we have clay in other parts of the garden, this was good, rich dirt.  Although I had stocked up on compost, I was able to build these beds without adding a great deal.

The key to planting on sloping ground is a good gravel mulch.  We’ve learned over the years to minimize digging, top dress and even out the ground with compost, and then mulch heavily with gravel. Finally, we pack this all down firmly with hands and feet.

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Columbine and Tiarella anchor this terrace. Two tiny lady ferns, grown from bare root starts, will one day flourish in this moist bed.

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We discovered that the first gardener on this property often used a large stone or hunk of concrete or brick to anchor shrubs he planted on slopes.  I’ve followed his lead and often anchor a newly planted shrub or perennial with something heavy to hold it in place until it establishes.

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Dryopteris erythrosora ‘Brilliance’ will eventually grow to three feet. This evergreen fern has interesting spring color on new growth. We have anchored it with stones as it sits at the top of the slope.

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We’ve been working on this new area over the past week or so.  We have been trying to fix the erosion ahead of the heavy weather forecast for this week.  The rains have shown us the weak spots, and where more work was required.  We had to go back and re-pack the area around the first Rhodie’s roots, for example.  And we also placed some stones above it to divert the flow of water around it from the slope above.

A front came through mid-day today, with torrential rain, about an hour after I finished the last of the planting and gravel mulch.  We were pleased that the terraces held.

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Additional erosion after today’s rain left roots exposed. It showed us additional engineering was needed where water pours off of the driveway.  The terra cotta pots helped anchor plastic bags to protect the Hydrangea on the right during freezing weather in March.  It is slowly recovering and finally pushing out new leaves.

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There were only a few spots of erosion, and only one Hellebore partially washed out on a terrace this time.  But the path along this slope was badly eroded.  Ligustrum roots were exposed where the path was washing away.

We studied the path the water took from driveway to ravine, noted where the gravel had washed out, and re-engineered parts of the project.  Translation: Back to Lowes for more concrete blocks, a few more bags of gravel and a bag of topsoil.

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Additional engineering should slow the run-off flowing into the path from heavy rain.  My partner placed the blocks to divert the water’s flow.  We’ve added topsoil and gravel over the Ligustrum’s exposed roots in the path.  Sadly, some daffies may be sacrificed in the process….

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We aren’t quite sure why the erosion on this bank suddenly got worse in the last year.  We must have made some small change in how the water flows, without even realizing it, when I planted the Caladiums last summer.  But whatever the cause, the problem was getting worse with each heavy rain.

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“Soil security”

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When you live on a slope, stable soil is a measure of security as heavy weather blows through.

We’ve created terraced beds throughout the garden, planted lots of shrubs and perennials, and dumped hundreds of bags of pea gravel on this property over the years.   We rarely visit our favorite garden center without adding a bag or two of gravel or compost to our order. It is an investment in holding the soil in place and keeping our home’s foundation stable.

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We trust that these new terraced beds, and the reinforced path we’ve created for water to flow down our sloping garden, will meet the challenge of heavy rain and the run-off it generates.  But more than that, we trust they will grow into beautiful additions which bring us many years of enjoyment.

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Woodland Gnome 2017

 

Note: I don’t often like to show parts of our garden that aren’t ‘beautiful.’   We have a lot of rough edges here in our Forest Garden.  It is a work in progress. I hope the techniques we use to hold the slope and garden on uneven land will help others trying to garden in similar circumstances.

I’ll show you this bed again as the plants grow in.  We trust that it will soon be one of our most beautiful areas, filled with photo-worthy foliage and flowers.  We expect it will attract the attention of our turtles, lizards and toads as the season progresses, too.  

For the Daily Post’s

Weekly Photo Challenge:  Security

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Columbine

 

 

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