Did the last wooden garden structure you built just rot away? Learn how to build long-lasting garden structures that will stand up to the elements outdoors.
Note: While this post is written with do-it-yourselfers in mind, you should also keep these tips in mind if you have someone else building garden structures for you. You can insist your structures are built a certain way and be leery of any contractor that wants to take shortcuts – they will be long gone when your fence falls over or your deck rots to the ground prematurely.
Building with wood is a great way to add structures to your garden relatively quickly and inexpensively. Wood is versatile as it lends itself well to various different finishes (stain, paint, naturally weathering) and is easy to work with using regular cutting and drilling tools.
But wood is an organic material that can rot away when exposed to the elements.
Severe weather such as winter rainstorms, windstorms and snowstorms hammers at the wood. In summer the sun beats down and dries out the wood, only for it to get wet again once the rainy season starts.
You want these structures to last.
You don’t want them to rot away after a few years.
After all you probably spent hours if not days painstakingly measuring, cutting and fastening lumber together for that one-of-a-kind structure that fits so well into your garden and supports what you are growing.
So how do you build long-lasting garden structures that survive in these challenging outdoor environments?
Here are some valuable tips that will help extend the life of any wooden garden project.
Tip #1: Use the best lumber
You should always pick the best lumber to use in your garden.
Rather than go into details here check out my complete post on this topic.
Tip #2: Use quality hardware
Not only should you use appropriate lumber that can produce long-lasting garden structures, but you should also use the right fasteners.
The right fasteners make the construction stronger, look better and last longer.
- Use screws and not nails:
- Outdoor projects may need to be taken apart occasionally such as to replace a part that did rot away or was damaged in some other way.
- Screws have a better resistance to joints pulling apart.
- You have less issues with marring the surface of the wood from errant hammer strikes.
- It’s debatable if construction goes faster with screws or nails. It really depends on what tools you use for each.
- Screws are more expensive in most cases, so factor that into the cost of your project.
- Use the appropriate screws for the wood you are using. There are special screws for pressure treated wood that won’t corrode from the ACQ preservative most PT wood uses.
- Where needed, use galvanized or zinc-coated lag screws and bolts. A good example is attaching beams to the side of posts.
Tip #3: Cover up end grain
Wood is composed of fibers that are oriented lengthwise in bundles. Think of a bundle of straws:
If you pour water in at the top it fills the straws with water. The same will happen with a piece of wood that is vertical when it rains. Even worse is when the bottom of the piece of wood is blocked from draining, but more on that below. It’s a recipe for rot and wood deterioration.
So it is critical that you cover the wood ends, which are called end grain, to protect them from water penetration.
Design your structures so that end grain is covered by other pieces of lumber. For instance if you are building with horizontal and vertical structural members, do it this way:
not this way:
Add a decorative cap on top of any posts. You can make them yourself from scrap offcuts of the same wood used to construct the beds. Or caps can be bought already pre-sized and often with a decorative chamfer.
Here are some cedar ones.
Or if you want a fancier, longer-lasting option here is a durable, attractive option:
To add some light to the top of your posts, especially if you use your garden at nighttime, you can also add solar-powered lighted post caps such as this one:
Tip #4: Elevate wood above concrete
Combine a post that is open at the top and closed at the bottom and you’ll have a saturated post that will rot away in no time.
Even if water doesn’t get into the wood at the top, standing water next to a post or structural beam that is attached or sitting on top of a concrete pad or footing can also rot the lumber.
This is called wicking and here is a good time lapse video of what happens when you soak wood from below:
So you want to ensure there is an air gap between the concrete and the lumber:
Use special brackets such as the Simpson Strong Tie ABA44Z Z-Max 4 by 4 Adjustable Post Base that you can install on the concrete.
They are designed to hold the end of the lumber just slightly above the concrete footing or pad. You can install them during installation by drilling a few holes using a hammer drill and then using special concrete screws.
The other advantage is that they are adjustable, so you can shift the post over slightly if it’s not quite aligned with the rest of the posts or structure. And you can cover the metal bracket with a wooden skirt.
Free standing items:
Use sacrificial wooden feet at the bottom of planters and other items that will be sitting on the ground or on hardscaping such as concrete or a patio. This will keep end grain off the ground but also allow the feet to be replaced when they rot away, rather than having to repair or replace the actual planter. I did this with my daughter’s planter box.
Use casters on planters as another way to lift the wood off the ground. And you have the added convenience of being able to move the planter around.
Tip #5: Special treatment for posts set in concrete
In order to have posts anchored firmly into the ground, you usually will need to cement the posts in.
Unfortunately this means that water can seep in and not be able to easily migrate back out of the post due to the surrounding concrete.
But there are a few steps you can take to minimize rot damage so that your posts last a longer time.
- Put a layer of gravel at the bottom of the post hole and set the post into the gravel so that when you pour the concrete it doesn’t seal the bottom of the post.
- Slope the concrete away from the post at the top.
- Once the concrete is completely dry, use weatherproof caulk (you can buy it in a gray or brown colour) to seal between the post and the concrete.
- Remember to cap the top of the post (not shown in the diagram below)
The alternative is to just use gravel to set your posts and tamp it well on all sides to lock the post into position. The idea with this method is that when the post gets wet, it can dry much more quickly if not surrounded by concrete.
However check if your local building code allows this – it may not be allowed if the ground is frozen in winter and there is a potential for frost-heave.
Tip #6: Seal tops of beams made from multiple pieces of lumber
If you are constructing a deck or other structure where you are building up beams made from multiple pieces of lumber, you end up creating a valley or groove where water can collect.
That standing water in that valley or groove can eventually create rot.
There are a few ways you can minimize water penetration in this situation:
- You can caulk the joint between the two pieces of wood. However caulk does break down so if you don’t have access to the joint (ie. you have decking over top of it) eventually you will get rotting issues.
- You can add a layer of self-adhesive roofing membrane on top of the beam to cover up the joint. Here is one I’ve used and it is easy to apply:
Henry BH200WB4559 Blueskin Weather Barrier Self-Adhesive Waterproofing Membrane, 50′ Length x 4″ Width
- You can add a galvanized washer or two between the pieces of lumber so that there is a gap that water can drain through.
Tip #7: Protect with paint or stain
Usually you will paint or stain the wood used in your garden structures to provide a more pleasing look. But coatings and sealants are also designed to protect the wood from rain, environmental pollutants and blazing sun.
- You can use paint or solid stain to unify all of your garden structures and make them look like they belong, even if they are constructed differently. However paint does not last very long and has a tendency to flake off, especially if the wood goes through significant heating and cooling cycles. Solid stain is better as it sinks into the wood and grabs hold of it
- Especially for cedar and redwood, clear or lightly tinted stain and protectants are my preferred coatings to allow the natural look of the wood to shine through. You will need to periodically renew these, especially on horizontal areas such as decks.
- For wood that is in constant contact with soil such as in raised garden beds or planters, you can line the inside with vapour barrier plastic to help prolong the life of the lumber. That’s what I did when I built my raised vegetable beds. And I did the same with my daughter’s 2×3 foot vegetable planter.
Have you decided you want the natural weathered look (namely a silver gray finish) or want to save the money and time on finishing? You can do that, so long as you expect the structure to not last as long as a structure that is protected.
There are some special protectants that do allow the wood to weather naturally but protect it from rotting and sun damage, but I have never used them myself as I prefer to maintain the beauty of non-weathered wood, especially when using cedar.
All of these tips of course cost some extra time and money and you may think: why bother, Marc? I just want to get that structure built as fast and cheaply as possible.
Yes, I’m here to tell you that you should bother.
In the long run these tips will save you time and money by having long-lasting garden structures. This will allow you to enjoy your tranquil garden rather than constantly repairing or replacing your structures. You also will help the environment as trees won’t need to be cut down to replace structures that have rotted away due to poor construction practices.