Never Build Planter Boxes out of Adobe

Never do it. They are a maintenance nightmare.  If you recently moved into a home with adobe planter boxes and the previous owner did not perform the necessary steps to waterproof the inside (which they probably didn’t), those planter boxes are probably in an advanced state of deterioration.

Early in my career I would repair these planter boxes. I soon stopped repairing or applying the SILOX ADOBE WATER REPELLENT on them as I gained experience from going to many homes for estimates. I observed how futile repairing them was when time after time I would see other contractors work falling apart. Below is a sample of the disclaimer I put on all my bids that reveals just how serious I am when I write that building adobe planter boxes are a mistake:

“All labor performed by ADOBE MASTERS comes with a limited four year guarantee.  If for any reason my repairs should ever fail, (outside of accidental damage done by you, family members, or guests…. retaining walls of any type where earth is pressing against the walls is not included in the guarantee) we will repair them at no charge.”

The vast majority of these planter boxes are filled with dirt and/or potting soil, with scant thought given to what the long term effects the water soaked soil that the walls are retaining will eventually do to the adobes.  Planter boxes, usually filled with water hungry plants, see only a little time before the water begins its destructive action.  They seldom have a chance to thoroughly dry out, and the damp soil and constant watering insure they never will.  Remember the mantra for adobe preservation: “Water is the enemy of adobe.”

Many people assume that if they regularly apply a water repellent to the outside of their planter boxes that this will slow down the rate of deterioration. This is simply not the case. The water from inside the planter box is what needs to be stopped.  Some desperate homeowners, appalled at the rapid decline of these adobes, resort to painting the outside of their boxes, believing that this will be the ultimate solution to their problem.  Unfortunately, this hastens the demise of the wall, for the paint will drastically cut off the ability of the adobes to release the water that becomes trapped inside.  The adobes will take even longer to dry out, if ever, and will slowly crumble behind the coating(s) of paint.

I have seen many cases of these “painted adobes” appearing to be in good shape. Upon closer inspection, the adobes can be seen to have developed a slight “bulge” where the water, seeking to escape, hits the inside of the paint coating. Unable to pass through, this water applies pressure against that same coating and causes the bulge.  This bulge retains the moisture, the adobe begins to crumble, and if you poke a pen or nail into this bulge you will find that it is filled with adobe dust…a sign of dying adobe.

What can you do if you own a house that has adobe planter boxes?  My recommendation depends on the condition that these planter boxes are in.  If they are in extremely bad condition with the adobes in an advanced state of deterioration, I would do nothing in the way of preserving or restoring them. Simply continue your usual watering routine, and when the planter boxes begins to disintegrate, remove your plants, demolish the wall, and have a mason build you a new planter box with adobe colored slump block.

Slump block, like adobes, are extremely porous, and literally suck up water.  The goal for having a planter box that does not deteriorate is keeping water from penetrating into the block. Before you put any soil or plants into this new slump block planter box, follow these procedures outlined in the following paragraphs.

Purchase enough SILOX WATER REPELLENT to thoroughly drench all four sides of the inside of your planter box or boxes using the before mentioned two-coat system.  Wait a few hours and then remove the soil that the SILOX has drenched along the edges of the planter box, as this soil will be hardened by the chemicals in the water repellent and will interfere with drainage.  The SILOX will act as an excellent undercoat for the material used in the following steps, and will help in the waterproofing qualities of the entire system (explained below).  Never rely on the SILOX by itself to act as a waterproofing system, for the chemical makeup is not intended for below-grade application. Used in conjunction with the following other steps, it is excellent.

If the planter box is constructed with one of the walls of your home used as the back of the box, thoroughly and carefully coat this house wall with two coats of a black, asphalt foundation coating that is specifically manufactured for below grade applications.  Take caution that you do not get carried away and coat too many of the adobe courses so that you will be able to see any of the black coating when you put the soil back into the planter.  To me, a sloppy job of tar splashed all over the adobes above the planter box where everyone can see looks terrible and amateurish.

Do this same two-coat procedure along the other three sides of the planter box.  One of the tricks to achieving a good job using tar is giving the first coat time enough to completely dry before you put on a second coat, and then to also let the second coat dry before you introduce any soil into the planter box.  This tar dries slowly, even in the blast furnace of an August summer, drying slower if the planter box is in the shade.

Don’t fret if it takes four or five days—even longer—for the coats of tar to thoroughly dry.  Two thin coats of tar are better than one thick coat, and make sure that you are covering the walls with complete coats of tar.  It is easy to miss spots and have small pinholes of uncovered adobe, which is one reason that I recommend a second coat.  This way you are decreasing your chances of missing any areas.

Allow this two coat system to completely dry by letting it sit undisturbed for a minimum of seven days—longer in high humidity. Then, take black plastic, the thick kind that you can buy at Home Depot that is used for placing a barrier between decorative rock and the ground to control weeds. Cut to fit this plastic so that it will cover all four sides of the planter box.  A couple of cautions here: never cover the bottom of your planter box with the plastic! You need drainage, and covering this bottom and then putting the soil on top of this would be a disaster for your plants.

Second, remember that soil will compact after it has been watered several times; the level of soil will drop in your box as the soil becomes compacted.  Insure that your plastic is several inches below the level of the finished soil so that you will take into account this compaction. Like tar, you certainly don’t want to see any black plastic sticking above the soil inside your planter box.

Finally, gently fill up your planter box with the appropriate planting soil, being careful not to tear the plastic by dropping rocks on it or knocking your shovel against it.  It helps to have someone assist you for this phase. An extra set of hands can position the black plastic and hold it firmly against the walls as the soil is placed.  Following these above recommended steps may insure your planter box will outlast the house.

If your adobe planter box that you have been watering is not in a terribly deteriorated condition, I would recommend the following steps to salvage it without having to tear it down and replace it with a more durable slump block.

First, remove the plants and soil. There will be soil left clinging to the inside of the planter box and lodged in the mortar joints, and it is important to clean all this off the adobes.  Either take a brush and whisk it away or take a hose and gently spray it off. Let the planter box air out for a full week­ (two weeks is even better) in the summer sun, and for at least two weeks if you are doing the project in the winter.

Next, follow the steps previously outlined for a new slump block wall.  Your planter box is now prepared for replanting; you should also consider having the damaged adobes repaired and then generously coated with SILOX PREMIUM ADOBE WATER REPELLENT.

Perhaps you are not interested in doing all of this work by yourself.  I recommend to my customers that, if they have a regular landscape company or crew that performs semimonthly or monthly service, to have them do the above procedures, or part of the heavier aspects (such as removing the plants and dirt) and then doing the rest themselves.  Or, inquire if the landscapers will do the entire project.  If they are trustworthy and you are confident they will do an excellent and thorough job without cutting corners, this will save you some backbreaking labor.

If you do not desire to deal with any of these recommended procedures, and wish to try and salvage your planter boxes, my final recommendation is to remove all of their water hungry plants and replace them with cactus or other low water use plants.