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This is a really simple rock wall.
Some simple ideas to build a cheap, but nice looking, rock wall.

How to build a retaining wall. An easy rock wall or a rock garden?

This project is for the homeowner with small retaining wall problems, lots of rock, and not enough yard space. This is no way an engineered wall! But low or well built walls can easily survive for 50 to 100 years with a little thought. Just make sure you reinforce them properly if people are going to be walking above them or they are holding up something important like your house! Look at the height of the wall. If it's greater than 4 foot and you can't push back another 4-8 feet to make the next wall, or the combined height is more maybe 20 feet, than you'll probably have to have an engineered reinforced concrete wall built. (Some communities limit you to as low as 2 feet, but usually it's 3 or 4 feet in height.) Length of wall doesn't matter. The wall can be 500 feet long with 500 feet of muddy soil behind it, if the shelves are wide, it is only the height that matters. I personally like to limit the height of each wall to bench height, about two feet. It's safer, much more fun to garden in, and has it's own seating.
Eriogonum grande rubescens,  Red Buckwheat in a rock wall. - grid24_6
native buckwheat  sticking out of a rock wall. California fuchsia, Yerba Beuna (shade) Lobelia dunnii(moist) also work in California walls.Look around in your area for plants that naturally occur in the rocks.
a garden step made of rock with California Fuchsia mixed in. - grid24_6
Do not get hung up on making a perfect wall. This is supposed to hold the dirt back and provide a place of garden or setting area. This is not supposed to hold a house up or support a bridge. So relax and be creative. Here's some steps that act as a wall.

Here's the basic construction methods of a cheap retaining wall.

A bunch a fence wire into concrete really makes a rock wall tough
Wire and cement at least the base of the rock wall if you need a long term wall. We've used expanded metal, barbed wire, chicken wire, orchard fence, etc.. Sometimes all the junk wire in the yard disappears behind the first large rock at the base of the wall and is filled with cement. Put a piece of pipe in every few feet for drainage. This is easy to do before you pour cement, hard afterwards. Pipe can be rubber, plastic or steel and it doesn't need to stick out, just provide a seep hole.

We're lucky and have gravelly, sandy decomposed granite that makes a decent mix.
1 Part Portland cement, 5 parts sandy gravel can be used and back fill and mortar. Don't expect it to make a engineered wall. It will be a ok wall, some here were done 100 years ago, and they are still here.

If you do not have our wonder dirt, mortar is usually a blend of 3 plaster sand and one cement, back fill is 3 plaster sand, two gravel and one cement.
Leave about 4 inches behind the rocks to stuff the wire in. If you want a better wall, buy some welded wire and actually clean out a 'ditch' along the bottom of the slope, fill it with 3 inches of mortar, place the wire into it and roll your base rocks carefully in place to make your bottom 'footing'. This makes your rock wall into a 50 year wall. Without this simple footing the rocks have a tendency to move. This footing is similar to a concrete retaining wall, just not as 'engineered'. The wide base needs to go back into the slope at least half as wide as the wall is tall. In other words, for a four foot wall, two feet wide.
welded fence wire - grid24_12
I'll usually make the bottom wall rock with cement and wire, a lot of wire. Chicken wire, non-climb fence wire, barbed wire, rebar, or old metal fence posts. Basically any wire or metal fencing laying around goes behind the rock in mortar as you construct the wall. The big rocks go on the bottom. I like to use a dolly to roll over the 300 pounders to dig into the bottom of the slope.

Here are some examples of Rock walls and Retaining walls

corner of rock wall - grid24_12
Sometimes broken concrete can make a good corner.
Corners can be fun. If you think a few of these rocks look square, you are right. This wall has a few pieces of concrete that we needed to get rid of in it. What better way to recycle!
This wall is about 30 years old, a little cracked, but still solid, again a wide wired base. Notice the vegetation covering it. (It's been in a greenhouse for years under constant irrigation.) This rock wall is home to many water loving plants including Wild Strawberry, Maidenhair fern, Red Lobelia and Columbine. This wet rock wall is also inhabited by tree frogs and an occasional snake! It is real popular with the reptiles and amphibians in the summer.
This wall has been in one of the greenhouses for thirty years. - grid24_12
This wall has been in a wet greenhouse for 30 years. Still solid, not cracks or rolls. It has a lot of cement and wire behind it.
a concrete foundation covered with rock - grid24_12
Use the same basic structure of a rock wall for a foundation covering 'rock wall'. If the concrete or concrete block is too smooth, drive some concrete nails in so the cement has something to grab.

If you're old, of small build, or fat and lazy, take longer and build a smaller wall. If you've got some big and strong help(for teenagers turn the TV, phone and computers off until the wall is done) build a wall with bigger rocks. Use tools! A little leverage goes a long way. And remember the big rocks go on the bottom so in most cases you don't have to lift them just roll them. Don't hurt your back. The wall does not need to be perfect! It's ok if it leans back here and there, the rocks look funny, not uniform, of different sizes and colors.

California fuchsia in rock steps - grid24_12
If you decide to build steps into the wall. Build little 7 inch (15 cm) mini walls with bare ground between them. Fill the bare ground with cemented flat stones and you'll have steps.

Dry stack rock walls

Dry walls have a few loose rules.

Don't make them very high, 2 feet is good, 4 feet you need to be good. The better the rocks fit together, the wider the rocks, the more the wall is planted, the more stable the wall will be. Big rocks go on the bottom! Slope the wall in a little as it gets taller, 1-2 inches per foot of height is the minimum. A 4 foot wall made of round 4 inch rocks is a bad joke. If those are the rocks you have, buy some sheets of plywood, build a simple but strong form to support same and make a concrete 'rock' wall.

Dry stack rock wall with California  native plants - grid24_6
The plants in the rock wall were planted about a year ago in the fall. They were watered a few times. They then survived the summer on no water with temperatures regularly exceeding 100 deg F. We had only 12 inches of rainfall that year!

These plants include California fuchsia, a colorful perennial that attracts lots of hummingbirds. It can be planted directly into the wall or near the top where it can drape over a bit. Another plant in this dry wall is Dudlea sp. It is also very drought tolerant and lives naturally in rocky outcroppings. It is also a big hit with the hummingbirds. The gray fluffy looking thing is actually a sage. This creeping sage looks great at the top of walls as it cascades down and is only 6 inches to a foot tall. It is also deer proof.
If the rocks available are shale, very soft granite(you can easily break it with a hammer) or any other soft, porous rock, make a dry wall. A cement wall with this material will often fail, because the rocks will just break off and fall apart. But if your soil is a clay, this soft rock makes a great dry stack wall. Layer of rocks, fill in voids with loose, dry dirt, next layer of rock. Try to nest the rock in between the rocks of the lower layer. Water the wall as you finish each day or every time you walk away for a break.
Dry stacks follow the same rules as a wired wall, but you are using clay instead of cement, and the wire only kinda works. If you're retaining wall isn't really retaining anything important, just making life easier, maybe you should build a series of smaller dry rock walls(no mortar or concrete) and have fun planting yourself a rock garden in each one.
Dry walls can be made of broken concrete, old tires(makes a great retaining wall to protect the 1964 Chevy pickup on blocks, behind the chicken coop) , logs(don't last long), concrete block (what's the point?), rocks, railroad ties (see logs) and almost anything else you can stack.
A Salvia Gracias on a rock wall - grid24_12
If your yard has rocks everywhere, great! Pick them up and make a rock wall, or place them next to each plant on the flat and call it a rock garden. If you live in Bakersfield, Los Angeles, or one of the other big cities with no rocks except by the pound from the local 'materials' company, look around for somebody removing some concrete. Broken concrete makes a great wall. It looks natural after you get a few plants growing into it.
No it;s not a pile of rocks. It's a dry California garden with two rock walls and some steps.  - grid24_12
These steps and rock wall were put in about thirty years ago when we had time put no money. Now we have neither?
The walls to the left are dry stack, the rest are mortared.

Build your wall around the plants. Figure out what kind of wall you want, plan it out on paper and in your head, then plan where in the wall you'll plant the plants. Don't make it into a stress session. This is suppose to be fun!

That's what's great about rock walls, they're very forgiving. Particularly if you plant them. I mentioned plants before, here's a few that occur naturally in rocky road cuts, rock outcroppings, and rocky knolls. Penstemon heterophyllus , Artemisia californica , Diplacus species , Dudleya , and Zauschneria like full sun. Ferns , Fragaria(strawberry) , Heuchera , Fringe Cups , and Columbines like moist shade.

dry stack wall with hole in it for plant, plant plant and jam rock back into hole right over plant - grid24_12

Leave small gaps in between the rocks in the wall for the plants. Jam the plant in, trying not to rip it up too badly, but it needs to be snug. You can also build the wall with a few well placed gallon sized rocks that are removable so you can insert the plant after the wall is built.

washing the dirt off of a dry stack rock wall - grid24_12
Every day, before you go in after working on the wall, get yourself a wine cooler, beer, iced tea, coffee whatever, and a hose and water in what you've done. Don't make a muddy mess out of it, just set the stones and water the plants.
If you want plan on building a patio or such you can use the edges of the pad as a retaining wall. Put some rocks against the form before you pour the cement. When you pop the form, was the cement off of the rocks. - grid24_12
If you make a cement retaining wall you can set rocks against the wall as you pour the cement you can create a 'rock' wall. Simply wash the cement off the rocks after you pop the form. You cannot do this on a high wall as you have to pop the form with the cement is not fully dry or you can't get it off the rocks.
The angle in this retaining wall is what gives it it's strength. - grid24_12
We've also used homemade concrete walls to act as retaining walls. This place has about 100 sq. ft of level ground. The back of the little hay shed needed a two foot wall for the 8 foot floor to be level. Cement is so heavy that the 2X6 forms failed in one section and we have a wavy wall. The wall was only 2 foot tall, but wet cement weighs about 100 pounds per cubic foot.
A curved rockwall can make a rock wall much more stable. - grid24_12
If you curve your wall and lean it in a little it will make it more stable.
The corner of the rock wall ran into a faucet. You could extend the faucet or make the wall shorter. - grid24_12
The lack of formality allows a rock wall to look good. If you make it too formal, you have to do a great job. If you do a good job and keep it simple, with a bunch of small mistakes, it will look good.
This rock-wall was used to cover a concrete foundation.  Not enough wire was used behind it and the mortar was not 3 sand to one plastic cement, but the wall turned out rather well.

To see more how to build stuff go to our How to build garden stuff

To see more More rock walls and garden walls.