I build some of those wooden pallet planters. I used heat treated wood pallets and stained the outside with a black stain, in the hopes that it would absorb more heat that way.
They'll be three years old this spring and the wood is holding up just fine. I live in a very wet place where everything rots quickly. Untreated wood left outside in the rain rots very quickly here. These seem to be holding up better than bare wood. I'm sure they'll rot eventually but they seem like they'll last at least awhile longer yet.
I'm not sure I'd really recommend them as a planting medium though. I've tried various vertical planting systems and haven't been all that happy with any of them. You can't get any volume of soil in any of them (these pallets are at least a bit better than gutters, hanging pots, or those hanging pockets/bags in that regard). Because there is so little soil and no really chance to develop any type of soil structure, mycrobial life, earthworms or insects providing nutrients for plants in these systems is a real problem. Solid organic amendments don't work (most of those need some soil life to break them down into nutrients the plants can absorb). You pretty much have to use liquid fertilizers. And quite frequently to keep plants healthy. Even with regular watering with
compost teas and fish based fertilizer most systems I've tried developed some type of nutrient deficiencies. I don't really care for all the extra work and inputs involved in having to constantly fertilize these systems.
They all also have problems with drying out. Again small amounts of soil mean little ability to retain moisture, different soil mixtures can improve this some but all all prone to drying. Watering can be difficult and gravity naturally causes the water to run to the bottom of the wall, planter, bags, etc. So the bottom layers can end up too wet, while to top sections end up too dry. Almost impossible to keep good moisture content even watering every day or twice a day. And I have these problems in a very wet climate that gets tons of rain. In a hot, dry climate these would constantly dry out.
The fact that there is so much exposed surface area and little soil volume means that soil moisture and soil temperate is greatly effected by climate conditions. A few cool, wet, cloudy days and your planters end up being cold and waterlogged. A sunny afternoon means they heat up fast. A hot dry wind and they turn bone dry almost immediately. In climates with variable conditions or lots of swings in temperature your plants go from freezing at night to cooking during the day. These swings in soil temperature and moisture levels are not good for the plants so most end up stunted and under preforming.
It's hard to plant a good poly culture in these. Faster growing varieties seem to quickly shade out or strangle slower growing plants. Those lush, full walls with lots of different plants, textures, colors, etc don't stay that way for long. Most plants have
roots that need more deep than these can provide. So you are very limited in what you can plant in things like the gutters, small hanging pots, or pocket systems.
In vertical planters where the plants are placed sideways (like the pallet planters and hanging pocket planters) plants seem to end up elongated and strangley as they try to turn upward to get more light or weight of leaves and fruits pull them down. Most plant stems are not designed to grow horizontal so they try to turn upright and get weird curves and turns in their stems as they fall over when they get too large, and then try to turn upright, etc. You end up spending too much time trying to rig up supports and keep new growth tied up so that steams don't fall over and break off with normal gravity. I think all this
energy the plants use trying to fight gravity prevents them from really thriving. The normal stem and branching structure doesn't provide support when they are turned sideways. Vinning plants that are meant to grow this way and have their own built in supports (through holdfasts or twining habits or tendrils) do much better. Some plants like tomatoes can be encouraged to vine and do ok. Any plant with a naturally bushing form won't do well in a vertical system. Even most lettuce, greens, and herbs which is often what you see in these systems don't seem to do as well as they do planted in the normal upright fashion. At least that has been my
experience.
If you set these up more like a hydroponic system where they are automatically watered with some type or nutrient rich water or fertilizer system they might do better. Something where they get a constant drip or mist watering and can be kept constantly watered to prevent the usual fluctuations. In a protected area where they don't get to much drying from wind, or too much scalding from hot sun, or too much cooling from night time temperature drops. Maybe in a very moderate climate or a climate controlled
greenhouse. But in the real world they just don't seem to preform as well as good old fashion planted in the ground systems.
If all you have is a wall or balcony and you have the time and energy to give these systems the extra attention than you can grow some things. But if you have
land and space to plant things in the ground they will almost always do better that way. If you want to grow food, almost all crop plants will do better in an in ground bed. At least that has been my experience with all the various vertical planters I've tried...which include the pallet planters, old gutters mounted to fences, various hanging pots and boxes, hanging bags, wall pocket planters, hanging upside down planters, and more.
If you want to pretty up a wall or fence these systems can work. There are some hardy annuals or landscaping plants like some succulents and grasses that can handle the stress and variable condition these type of planters provide. Or at least that is my understanding. I've not personally tried that route. I'm more interested in growing food and I've yet to find a vertical planter that excels at this.
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