Deciding to stain your new wood deck can be an exciting and easy weekend project. It should only take a couple of hours, and the deck will be protected from the elements. But deciding which deck stain to get is important for one big reason.
Some wood deck stains will kill or harm your plants if they come into contact with each other. The chemical and preservative make-up of these wood stains can cause brown spotting on leaves, lack of water uptake, and inability to absorb sunlight in your plants.
The good news is there are new products and natural stains on the market to keep your deck looking good all year. Keep reading to learn all you need to know about plant-killing oil-based stains and the environmentally safe water-based wood stains.
What Is in Wood Stains?
Deck stains and oil-based paints have been found to be toxic to humans, animals, and plants. All oil-based stains (not just for decks) have been put under environmental scrutiny in the past twenty years for having a high level of VOCs (volatile organic compounds).
Green America reports, deck paint and stains have been found to contain harmful biocides, pesticides, fungicides, and added dryers.https://greenamerica.org/green-living/eco-friendly-paints-and-stains (source)
The different components of wood finishes include:
- Pigments or dyes to add color to the wood.
- Resin, the natural or synthetic binder in stains. Resins include alkyds, acrylics, cellulosics, polyurethanes, vinyl, and oils.
- Solvents and/or thinners are used to keep the finish in liquid form. Organic solvents such as ketones, glycol ethers, alcohols, petroleum distillates (mineral spirits, toluene, xylenes, and naphtha), and turpentine are used in most stains.
- Various additives are used to adjust drying time, prevent fungus/mold growth, and thicken the wood finish.
The US Environmental Protection Agency (EPA) defines a biocide as “a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products.”
In short, wood stains have these harmful chemicals to minimize the rot of your deck. Except, they are harmful to all living organisms, and this includes your plants.
How Do Deck Stains and Sealants Kill Plants?
If you aren’t careful when staining or sealing your deck, you might spray the liquid onto nearby plants. Most information available on this subject relates to the harm of stains for human contact, but if it hurts your skin, it isn’t good for plants either.
The preservatives in stain will prevent plants from absorbing water, nutrients, or sun. If any of the stain gets on the leaves, you may see brown spots, or the plant may wither away.
A few sources like Green America, The Green Seal, and Allergic Living suggest preventing wood stain and finishes from entering your garden soil. In plants, this can damage their roots, and they won’t survive. It is also important not to ingest any edible plants that have come into contact with contaminated soil. Like the EPA stated earlier, these stains contain poisons.
Does Stain Kill Grass?
The effects of deck or fence stain on grass are moderate. If the stain comes into contact with your grass, there will be some discoloration or death along the bottom of your fence line. Grass will typically bounce back within 3 to 6 weeks as long as the grass is well watered.
How to Prevent Stain From Killing Plants
Protecting your plants and grass from deck stains is simple. Cover them with a tarp or plastic sheeting, but not too tightly so as not to suffocate the plants. If the plants can be moved, move them to the other side of the yard until the deck is fully dry.
It’s generally suggested that you cover nearby vegetation to prevent stain from damaging it, and any other surfaces you don’t want stain residue on.
Ready Seal gives the same suggestion in their FAQ section on their website. “Light overspray may not kill grass or plants, but yellowing/browning may occur. Heavy overspray and spills can kill vegetation.”
With any wood stain, it is advised to use a brush instead of a power sprayer, as the stain will travel more easily to the surrounding vegetation and travel through the wind when using a sprayer. Although spraying is my preferred method, if you have nearby plants, you may need to brush.
Here’s a quick video exploring rolling, brushing, and spraying stain on a deck.
What to Look for in a Stain
Check VOC Level
In 1999, the EPA put into effect the Clean Air Act, which in part required architectural coating manufacturers to monitor the VOC level of their products. Oil-based wood stains had incredibly high VOC levels and made up 9% of VOC levels in the atmosphere.
The current standard for VOC levels in wood stain is under 250 g/L and under 350 g/L for varnishes. Many companies have solved this requirement by making their stains water-based, and some have committed to creating 0 g/L VOC stains and finishes.
The EPA requires manufacturers to put the VOC level of each coating product on the label. When deciding which stain to choose, read the label first.
It has been 20 years since the EPA passed the Clean Air Act, so you are more likely to walk into Home Depot or Lowes and find mostly water-based deck stains. In fact, both Home Depot and Lowes committed to only stocking stains that met the VOC requirement.
Water-based deck stains do not act the same as oil-based. The old oil-based stains would penetrate the wood of the deck and make for a longer-lasting finish. To comply with the EPA, companies have started to improve the water-based formulas, which lay a film on the surface of the wood instead of penetrating it.
Companies have improved the water-based formulas to:
- Contain higher solids content
- Reactive dilutents
- New types of solvents
- And/or co-solvents
- Other non-traditional substituents
Choose a Natural Oil
There is a large movement for using natural oils and waxes instead of harsh chemicals. Some natural alternatives include:
- Raw Linseed Oil
- SoySeal Wood Sealer and Waterproofer
- Soapstone Sealer and Wood Wax
- Homemade Milk Paint
- Homemade Beeswax and Jojoba Oil Wood Conditioner
While some of these options are increasing in popularity lately, they will require more maintenance and additional coats more often.
Is Thompson Water Seal Toxic to Plants?
Thompson Water Seal offers a low VOC option, but most of their products exceed the industry standard. This is stated as “Exceeds Industry Standard ASTM D-4446 for Waterproofing Wood” on the back of the label. For this, Thompson Water Seal pays a fine for each product that doesn’t comply with the Clean Air Act.
There is no direct evidence Thompson Water Seal products are toxic to plants, but considering the high VOC level of most of their products, it probably will damage your plants (if sprayed on them) like other oil-based wood stains and finishes.
If you are going to shop for a clear finish like Thompson’s Products (link to Amazon), make sure to find a water-based sealant that complies with the industry standard if you will be spraying near plants. There are plenty of options online.
Wood deck stains and sealants have come a long way since the 1990s, but it is still a good idea to cover any plants and grasses surrounding your deck before staining. Make sure to find a stain with water-based on the label, and that it states compliance with the low VOC levels.