We often get asked if the Corten Steel Planters will stain the adjacent area by producing rust runoff or by being in direct contact with the surface the planter sits on. Below are some pictures of a Corten Planter that has been weathering in the same spot on the patio for about four months. The outside of the planter is completely covered with rust and the patina will act as a protective layer and prevent any further corrosion on the outside walls of the planter. From the pictures you can see that there is very little rust run off (virtually none). At this point the planter is weathered and the weathering steel should produce very little to no rust run off. A point to consider is that Corten Steel (weathering steel) seals and fully weathers best when it is repeatedly exposed to moisture and then is allowed to dry. Thus the amount of rust run off could vary by climate. As a reference the planter in the pictures is happily weathering in Seattle.
Also, staining will occur were the planter metal comes in direct contact with the surface the planter sits on. If you are placing your planter box on grass, lawn or dirt than there is nothing to worry about. Or if you never plan to move the planter you will never see the marks it leaves underneath the floor. But if you plant to move the planter and do not want rust marks you should make sure the planter metal does not come in direct contact with the surface that can be stained. For our planters this can be achieved by placing a plastic strips on the channel feet/legs the planter sits on. Another, solution is to place the metal planter box onto casters. Placing the planter on casters will eliminate direct contact and allow you to easily move the heavy planter.
Generally, If you cannot stand the ideal of the smallest amount of rust on your deck or patio Corten planters are probably not ideal for your application so consider other metal planter options like Stainless Steel or Powder coated aluminum.
Aluminum is a very strong yet lightweight alloy that is well suited for construction of large metal planters. Aluminum is naturally rust-resistant and can be powder coated in just about any color. Powder coating is a durable and environmentally friendly coating process that contains no volatile organic compounds.
Unlike some plastic planters that can crack in freezing weather, or bow in hot sunny conditions, aluminum retains its structural integrity. See some pictures below of a 20”x20”x20” aluminum planter enjoying the sunshine, and in the winter being frozen solid. Planting in durable metal planters eliminates the need to winterize the containers by moving them inside to shelter the planters from extreme weather.
Recently I helped a friend build a brick patio in front of his new house. The court yard area sloped down towards the front entrance so we had to level the patio area by digging up the dirt and installing an interlocking brick retraining wall. The brick patio and the brick retaining wall was a fairly strait forward installation. One issue that came up was that on each side of the retaining wall we had a sloping fence and exposed soil. Extending the retaining wall on each side would have cost more money and a side retaining wall that is just one or two bricks high would look awkward. So we decided to use the rocks that we dug up in the process of leveling to cover up and hedge the exposed dirt. Then we placed a Corten Steel (also known as weathering steel) planter box on each side to cover up the rocks and give the patio a finished look. The combination of the rocks and extra long Corten planers provide a natural transition for the sloping sides which would have been difficult to achieve with brick or other hedging solutions.
The two grades commonly used for outdoor planters are 316 grade, known as marine grade, and 304 grade, more commonly used for outdoor planters. Both grades are suitable for use at inland locations whereas 316 grade is recommended for use in coastal, marine or heavily chlorinated environments. Our standard planters come in 304 grade stainless steel with a fine brushed finish.
To periodically clean the planters use non-abrasive cloth and warm water with or without a gentle detergent. Always wipe with the directional grain of the steel. After washing, rinse with fresh water and dry thoroughly.
Salt water air and other chemical may result in small brown spots appearing on the surface of the planter. The spots can be easily removed by gently rubbing the surface of the steel, in the direction of the brushed finish, with a Scotch-Brite pad.
Stainless steel will not rust but it is vulnerable to salt air and chlorine. 316-grade stainless steel is made with molybdenum and is manufactured for costal use. The molybdenum provides higher resistance to pitting and crevice corrosion and gives 316 better overall corrosion resistant properties.
A stainless steel planter will provide you with years of use and enjoyment without rust.
My neighbor taught me this trick after she purchased one of our Corten Steel planters. She uses empty plastic water bottles to fill up the planter about half way and then fills the planter up with dirt to the top.
This approach has several benefits:
1) The planter is not as heavy because half of it is filled with air that is inside the empty water bottles.
2) You can use less dirt to plant.
3) Plastic bottles at the bottom of the planter allow for excellent drainage.
4) Plastic bottles at the bottom of the planter promote air circulation and will help to keep the roots of your plant cool.
5) This is a great way to reuse the bottles which may otherwise end up in the trash.
Tip: make sure the water bottle caps are nice and tight on the bottles. Each bottle should act as an air bubble and keeping the caps tight helps ensure the bottles do not collapse under the weight of the dirt.
Say you are filling your planter box or flower pot with dirt on the deck or inside the house and you do not want dirt coming out from the drainage holes, but you still need the planter to drain. You can run to home depot and get some landscaping cloth (about $10). But why do that? Just line the bottom of your planter with newspaper or brown paper grocery bags. The paper will allow the water to drain while keeping the dirt from falling out. Also the paper will retain moisture, so less frequent watering needed.
I would stay away from using magazines, as all that paint on magazine pages will most likely prevent water from draining.
Our Corten Steel Planters are made to rust and will start showing the signs of rusting if you just put them outside for a couple of weeks and let Mother Nature take its course.
If you do not want to wait for a couple of weeks, wash the planter with warm water and soap when you first receive it. This will remove any remnants of oil and the water will react with the metal initiating oxidation (rusting). A periodic mist of water will accelerate the oxidation process, especially if you are in a dry climate.
Spraying vinegar onto the planter will give it the rust look in a matter of minutes. This rust however washes off, so the next time it rains, your rust will be gone. The planter really just needs a few months, with or without vinegar, to gain a natural layer of rust and seal.