If you are just building or have just built a raised bed then you probably have two questions right at the front of your mind. What do you fill it with and what should I line it with. Let’s have a look at the lining question right here and now and see if you even should line your raised beds, and if you do, what material to use.
What to line raised beds with?
If you are going to line the sides of a raised bed in order to try to make them last longer then you want to use solid plastic.
The black landscaping plastic you can get will work well. By using this plastic you can stop the dampness of the soil from transferring into the wood of the raised bed. This will help it keep drier and should help it last longer.
I wouldn’t use the breathable weed membranes that you can get. This is because as the name suggests it is breathable which means there are holes in it which will defeat the whole object of using it to preserve your wood.
If you want to recycle or just save yourself a little money then one thing you can do is use old compost bags for your lining. You can turn the bags inside out so they are just black and staple them together to your raised bed. This gives you the same effect as using the black plastic lining but it’s free and recycling plastic instead of throwing it away.
Lining the bottom?
Should you line the bottom of your raised bed? Well, this depends on where it is, but in most circumstances, I would say no you shouldn’t.
The only time I would advocate for lining the bottom is if you are building the raised bed onto concrete or some other solid surface. If you are putting it onto grass then I wouldn’t line the bottom.
I can understand why you might be tempted to do this to keep weeds down but there are other ways to achieve this. If you line the bottom of your raised bed with plastic then you are limiting its depth. Remove the lining and you can use the soil underneath as extra room for growing root vegetables.
It will also allow beneficial creatures like worms to enter your soil and start improving it.
How to kill weeds without a liner
If you are putting your raised bed on the grass then you will obviously need to do something about the grass to stop it from just growing up through your new raised bed.
What I like to do is cut the grass really short with a strimmer, I’m talking punitively short here, you are trying to hurt and weaken the grass.
Once that is done I put a thick lining of cardboard down on top of the grass. This will cut out light to the grass and kill it off over time. But unlike plastic, it will degrade and rot away, so you kill the grass but then the cardboard disappears.
You want to make sure you only use plain brown cardboard and not printed cardboard as god only knows what chemicals are in that. You also want to ensure there are plenty of overlaps to make sure there is no chance of weeds being able to see some light and grow through the cracks.