Question
QUESTION: We have an outside deck off of the second story of our home.  It connects one area of our home to another and we love the inside/outside feeling it provides.  The deck is finished with Elastomeric.  We just had our deck redone, and it was very expensive.  We have great potted trees (2 ficus, a plumeria tree and hibiscus tree) that are very large.  We also have smaller plants.  We'd like to put these plants back on the deck, but we have staining issues.

Every time we water, a stream of brown water (from the soil) comes out of the bottom and stains our deck.  Is there a way to prevent these brown stains?  Even the smaller plants with dishes have brown runoff water (although not as much as those that don't).  The pots that hold the trees are very large and don't come with dishes to catch the water.  I need to soak the plants well because we live in California, where it's hot and dry.  Is there a special soil we can use to repot our plants that will prevent this?  

In addition, black circle stains develop under the plants.  I read that we need to raise the plants off the deck to prevent the black circle stains, but I'm unable to find stands large enough for our trees.  I've searched the internet and building supply stores and haven't found a stand that will accommodate the trees.  Is there a way to prevent the black stains under the large potted plants?

Thanks for your help.

ANSWER: Hi, Bill.  Three or four things I read into your question: You have 1. Very Large potted trees, 2. brown/black stain issues, and 3. drainage over elasomeric decking, and 4. dirty & frequent watering.  As to staining, the organics in your soil are being washed away with the water and depositing themselves on your nice, new deck surface.  I would do two things: add a polymer to the soil that aids in retaining the water and making it available to the plant (google "soil polymer crystals" for many brands available).  Just sprinkling it on the surface does no good; It has to be mixed into the soil at the root level.  When/if re-potting, I would line the bottom of the large pots with landscape fabric.

In commercial applications (a parking deck), we added drainage as a part of the planter box, and piped into the rain gutter system.  Full-sized trees get heavy, so we removed some soil weight by using blocks of floral foam in the planters.  It also added insulation for our colder climate. Your deckscape application is sort-of an after thought, so your goal is to somehow collect or re-direct the drainage off of the deck surface, either by using plant-pans/trays or by direct drainage through the decking surface, depending.  It also depends on what openings are available to you --scuppers, gaps in the deck surface, under the railings, or existing surface drains.  Avoid directly draining off to the sidewalls, as this may discolor your first-story walls with drainwater.  This may not be easy, if you have a full-blown, solid, 6-layer CMFPS elasomeric deck! (like the one shown here: www.prestigedecking.com).  

Water heaters have a drain pan system that would work (http://www.oatey.com/products/pans-and-stands/water-heater-pans/aluminum-water-h), but they are not very attractive for a deck application.  So too, an outdoor shower pan (http://www.gardenista.com/posts/hardscaping-101-outdoor-showers)  The ones shown above are custom-made, stainless steel.

Any tray or drainage device directly in contact with your finish is going to trap water & gunk and discolor it.  Hence, other people's suggesting you raise the plants off of the deck, which is a good idea.  You can raise large trees off the the deck by using pots with small "legs", or add squares of tile or brick at the corners/edge.  Not a perfect solution, but it lowers the area of contact on the new deck surface.  Example here: http://www.allmodern.com/NMN-Designs-Square-Planter-Box-SP1-PSP1052.html  I have not had good success with self-contained pots that are supposed to "eliminate" run-off.  They tend to over-water and kill the plant at the roots.

Ultimately there will be some discoloration, if from nothing else the tree pot shading the deck surface from sunlight & UV damage.  So once a plant spot is chosen, try not to move the pots around too much.

Finally, I am assuming that these very large trees & pots are not excessively loading your structure (1 cubic foot of dirt/tree weighs about 80 lbs. & water by itself weighs 63 lbs/cubic foot).  So, a 15 foot tree in a 3 ft pot adds about 1/4 to 1/2 ton to your deck, and another 200 to 300 lbs. when you water it.  If the deck was designed correctly, it should be no problem for your four, larger plants.

Sorry. I don't have a "magic solution" for you.  Perhaps a new landscape invention waiting to be discovered!

---------- FOLLOW-UP ----------

QUESTION: Thank you.  We're planning to repot and I'll add a polymer to the soil at the roots when we do.  How much should I use?  Regarding landscape fabric, do you mean weed resistant landscape fabric?  Also, should I line the inside or outside?  I'm sorry, but I have only basic knowledge about these matters.

How does using foam in the planters impact the plant's roots?  Doesn't it need the soil?  Yes, our trees are heavy and now they're in plastic containers.  I'm afraid to use ceramic on the second story.  I was going to buy new plastic containers with pans to catch the water.  The water on the deck drains through two drains in the deck.  The deck is slanted toward these drains.  The deck also has a hole on the side for additional water, but the plant water doesn't drain through it.  I visited prestige decking, and, yes, our deck is covered in the grey elastomeric shown on the site.

I found a garden center in Marina del Rey that has different types of feet that raise the pot above the deck surface. I was told this will prevent the black stains. These feet work on all types of planters.

Thank you very much for your help.

Bill

Answer
The polymer is mixed in at a ratio depending on the manufacturer's recommendations.  Typically, for a 3" caliper tree/24" box, you add only 8 to 12 oz., or about 1 to 2 oz. per cubic foot of soil.  More for sandy conditions, less for clay soil.  It doesn't take much to improve the water retaining ability of the soil.  The polymer crystals can store up to 200 times their weight in water and last about 3-5 years. I also use them in our dry desert in the veggie garden.  They are inert & harmless to humans.

Regarding the fabric, yes, a weed resisting fabric placed on the INSIDE of the pot, to retain the soil fines that are leaking out of the bottom of your pots.  

The foam is blocked in at no more than 1/3rd of the pot volume and along the inside wall of the pot.  You fill in the rest with your growing medium (the fancy term for "soil") that the tree/plant lives in and holds/hides the foam filler.  Imagine it like a pie, and the foam is the thick crust, and your plant is a wine glass in the middle of the growing medium filling.  I plan for the plant to grow, and so plant them in larger pots so I don't have to re-pot as often.

The feet you found may do the trick.  Hope these suggestions help.  ~m