The question of what material to put under a deck is a question both of aesthetics and function. Not wanting to place anything that will damage your deck. At the same time, a deck should look clean and tidy underneath.
The best material to put under a lower deck is landscape fabric covered by non-organic material like gravel or rock. The landscape fabric to stop weeds from overtaking your deck, the gravel to hold down the fabric while allowing for drainage.
Is there anything that makes a deck look more neglected then a weed poking its head through the decking? If not addressed during construction forevermore, you will be fighting a losing battle against weeds. Pulling only the top of the weeds off will leave them returning in a few days. Herbicides may kill them but with the possibility of damaging your decking with harsh chemicals. Besides, you can only spray them one at a time. Tomorrow more will come.
The ground under low decks should be covered with landscape fabric and gravel.
Let’s start with the visible material under your deck, but don’t ignore the need for weed control. Controlling weeds under a deck is best done with landscape fabric. Please read to the end, when we discuss what landscape fabric to use under your deck. But starting with the visual, the material holding down and protecting the landscape fabric.
Protecting the Fabric with Non-Organic Drainable Material
Material holding the fabric down under your deck must be non-organic. Mainly, that it does not absorb water while allowing water to drain. Organic material such as bark mulch or wood chips as they will absorb water and decompose. The wonderful fungi that break down compost for your plants, unfortunately, will also break down the wood of your deck. Best not to encourage its development under your deck.
Non-Organic material also will not breakdown over time, but organic material will. Bark mulch may look amazing for the first few years, but as it decomposes, it will need to be refreshed. Under a deck, this becomes difficult. Keep the bark for around your bushes. They will love it.
Larger Than ¼” non-organic Material
Landscape fabric only stops light but is not strong enough to stop roots. Taproot weeds like dandelions easily cut through the fabric from the top. Sneaking their roots through the permeable fabric and ripping a hole for their roots. Material holding down the fabric must be large enough as not trap moisture allowing weed seeds to germinate and grow roots.
Dirt is absolutely out of the question. Sand will also trap water allowing the seeds to germinate. Using material screened to larger than ¼” will prevent the material to compact together enough to hold water, germinating the seeds.
Non-Organic Material or Gravel Coverage
Gravel should be spread out to a depth of 2” (50mm) over the landscape fabric under your deck. Deep enough to cover the fabric and prevent weed growth. 2” is also a nice working depth for raking the gravel. It takes about 1 yard to cover 100 square feet 2” (50mm) deep. A 200 sqft deck, requiring 2 yards. Rake it out level with the rake upside down for it won’t catch and tear the landscape fabric.
Popular Non-organic Material for Under Decks
Gravel is the most common ground-covering under decks. Being non-organic with excellent drainage is a natural pick. Here are a few gravel options plus three non-gravel ones.
Economical Under Deck Material
For decks less then 24” (0.6m), the main concern is weed control. Economical material to hold the landscape fabric down protecting it for years.
Screened Crushed Rock
Rock which has been crushed or broken down into useful sizes. It’s important that it is screened to avoid sand and other small particles acting as weed nurseries. Not amazing in colours but coming in off-white, grey, reddish-brown and tan. Nothing really to look at but one of the most economical covers for landscape fabric. A deck with skirting this is an ideal match, nothing fancy but at a good price.
Natural Washed Rock
Similar to crushed rock, except it often riverbed 14-25 mm (3/4-1”) gravel, washed to remove small particles and dirt. Coming from riverbeds along with the washing process, I find that they are often more rounded stones. Giving a softer look as opposed to crushed rock angular appearance. About one and half times more in price as crushed rock depending on regional availability but often with greater variety in gravel colour but not sold based on colour. Limiting your selection to what is delivered.
Think big washed rock, 40 mm (1 5/8”) or larger rock cleaned to prevent weed growth and allow drainage. Its size is both its advantage and disadvantage; the large size ensures that weeds will not grow with no compacted fine particles for germination. The disadvantage is that it’s harder to place. The larger size is harder to rake out level. With your rake often bouncing as it hits larger, heavy stones. But it does provide the best drainage for under your deck. Costing slightly more than crushed rock. Not my first pick in ground-covering under a deck but if drainage is a concern, it will work well.
Under Deck Ground Cover to be Seen
Decks higher than 24” (0.6m) without skirting may look better with more visually appealing ground cover. Adding both colour and style under a deck.
The name says it all, small rocks about the size of a pea, between 1/8”-3/8”. A very small but beautiful decorative stone. Coming in a range of different natural colours like buff, rust-brown, shades of gray, white, and translucent. Rock to be seen, a higher deck with no skirting, this is an excellent choice.
I love the feel of these small rocks running through my fingers, probably why you will often find pea rocks around playground equipment. A beautiful, small rock that keeps down weeds looks good and feels great on your hands.
A possible option for an open deck without skirting high enough to view. Rundle rock is similar to crushed rock, angular is shape but a charcoal colour. When sprayed down, the depth of its colour is renewed. A nice dark colour for under a deck.
A pricier option for material under a deck. Costing around two and half times as crushed rock. Only a good option when viewed, the deck needs to be high enough and in a prominent place of the yard to enjoy its dark colour.
Similar to natural washed rock except with a rainbow of colour. With a wide range of eye-popping colours in a convenient levelling size. Get ready to pay for this beauty as rainbow rock is often over twice as much as crushed rock. If your deck is high enough and would like to add some more colour under your deck, rainbow rock is a good option.
A good decorative stone but an earth tone colour, as the name says “Tan.” With pressure-treated decks often stained brown, this is a nice complimentary lighter brown colour to go under it. Not attention-grabbing but a calmer colour without going grey. Cheaper than most decorator stones but more than crushed rock.
Non-Stone Material for Under a Deck
Stone is always my first option for under deck material. It is natural, durable and suppresses weed growth, but if you are looking for something different. Here are some possible non-organic options for under a deck.
Shredded Rubber Mulch
Shredded tires similar in appearance as wood mulch but not organic and will not decompose. Often a darker colour as its natural tire state but can be dyed for more natural colour. Lighter in weight then stone but sticking together minimizing movement.
Some rubber mulch’s drawbacks are with the fact its not natural. On hot summer days, it can off-gas a rubber smell. Hey, if you like to go down to the drag track on summer days, this might be ideal for you. It will also leak chemicals into the soil, destroying soil health, not a big deal because you don’t grow vegetation under the deck but something to make a note of.
It not being a “natural” product is very effective in weed suppression. Weeds want nothing to do with it, which is advantages. Promising to last over 50 years, it will outlast most decks except for maybe your Ipe decking.
Crushed Recycled Glass
Crushed tumble glass, with soft non-cutting edges, glimmering amazing vibrant colours. If you want the material under your deck to be the star, glass may do it. There are few materials with as much life and colour to put under your deck. Sparkling with vibrant blues, purples and greens plus many more colours, crushed glass is the most decorative of under deck options.
With pricing starting at around $40 a square foot, this is going to be costly. More costly than your composite or even Ipe decking. Possibly better to be used to add colour to spot under a deck without covering the entire area.
Possible Organic Material for Under a Deck
You do not want bark mulch, wood chips or any other material decomposing and trapping moisture under your deck. But if you have a deck high enough to work under but to low to enjoy as a shaded patio. A deck between 3’-5’ (1-1.5m) high, an option is low growing ground cover plants.
Plants under a deck must be shade plants, thriving with little sunlight. Also, they must not grow too tall, reaching your deck or poking through the decking. So, ground-hugging, low light thriving vegetation.
“Pachysandra is perfect for planting underneath decks”John Walke
Some other options for low growing, shade-loving vegetation are hostas, coleus, impatiens or begonias. Once established, it will green up the ground under the deck but will require time to take hold and cover the ground under your deck. You will be spending much time initially, crouched over planting and then caring for them but brining life under your deck.
If you do not go with intentional vegetation under your deck, you will need to control the weeds. Even gravel 2” (50mm) deep will not sufficiently stop weeds.
Landscape Fabric Under Gravel
The fabric is to stop the weeds, the gravel to hold the fabric in place while allowing drainage. Our greatest concern being weeds. Let’s consider what does landscape fabric does and what should we look for when buying?
Landscape fabric does not kill weeds. Let me repeat myself. Landscape fabric does not kill weeds. Landscape fabric is designed to block light. Without sunlight, weeds cannot grow. If you block the light, you stop the weeds.
Since landscape fabric does not kill weeds, it is best to remove all weeds before building your deck. Pulling out the bigger weeds and spraying the smaller ones to ensure that they do not push through the landscape fabric reaching for the light. Landscape fabric can stop seeds from sprouting but established weeds need to be removed before installing
There are many levels of quality of landscape fabric.
You will want to install a quality fabric lasting many years. Wood decking lasting between 15 -20 years depending on care, composite decking lasting 25 plus years. The landscape fabric needs to last as long as the deck, as you will not want to be replacing it during the life of the deck. Low decks are hard to work under.
Quality landscape fabric is heavy compared to lower quality fabric. A 150 square foot roll weighing 20 lbs or more will be a thicker fabric lasting longer. Sometimes the fabric will be labelled base on weight, 5 once or better is good.
Some landscape fabric is also UV resistant but is not required under your deck as both the deck and the gravel will be shielding the fabric. Think flat roofs and gravel. It’s the tar that stops the rain, but the gravel protects the tar from UV.
Some fabric will come with a warranty based on years, either 5, 10 or even 25 years. The challenge is under what condition will it last that long. If all other things being equal if it promises additional years, then use that one as any additional years stopping weeds under your deck is a good thing, especially if it’s only a few extra bucks.
Speaking of cost landscape fabric will cost between 5 to 15 cents a square foot depending on the quality and size of the roll. Per square foot, you will save more money buying a larger roll.
A 20’x12’, 240 square foot deck will need roughly 300 square feet of fabric and 144 pins when accounting for overlap.
Stopping Light Not Water
The challenge with landscape fabric under your deck is water. All material under your deck needs to allow water to drain. Pooling water under your deck will raise moisture levels increasing wood rot and mould. The landscape fabric must be permeable to water. It is better if the fabric designs are permeable to water than perforated after.
Also, helpful limiting water under your deck-levelling out the ground removing areas in which water can pool. Then when there is a downpour, the water will run out from under your deck unto your yard. The grass will love it and the deck will last longer.
Speaking of water, always make sure that the downspouts of your house are directed away from the under the deck. The increased water will become trapped under your deck with the decking shading it, slowing evaporation. The increasing moisture level under the deck will increase rotting, destroying your joist and decking.
Roll out the landscape fabric with the rough side down, helping the fabric to stay in place as you work. Pin it down with landscape pins every foot or so. Keeping it in place till you have the gravel on it. To ensure that no weeds sprout between layers, overlap 6-8 inches.
Landscape fabric alternative
Plastic is not permeable and should not be used under your deck. Plastic will trap water under your deck, causing damage. Also, small pools of trapped water becoming breeding grounds for mosquitoes. These pesky insects will annoy you to no ends while you’re trying to relax on your deck in the cool of the evening.
Using Cardboard or newspaper instead of fabric to suppress weeds? I love this idea in my garden. Just recently, I did it around my raspberries bushes to save on weeding and increase moisture in the ground. It worked wonderfully, weed-free garden all summer, with thriving bushes.
“it takes approximately 2 months for cardboard to decompose.”Reference
But I will need to replace it again in the spring. Cardboard will not last long enough to stop weeds for the life of your deck.
It’s a good idea to edge the gravel with landscaping edger. This doesn’t need to be expensive or complicated, but something to clearly define where the deck ends and the grass begins. Otherwise, your deck gravel will start spreading out into the lawn and the grass will start growing under the deck. Making your yard look messy. Besides, you don’t want to be hitting gravel with your mower.
A roll of plastic lawn edger is the most economical and easiest to install. You can also fence off the gravel with a treated 2×4 on edge or pavers, giving it a more rigid and solid look. Whatever you choose, a clearly define yard will keep your yard and deck looking good.