What is a good alternative to pressure treated wood for raised beds?

Question

I've had my pressure treated wood raised beds for my vegetable garden since 2005 and was recently made aware of the potential risks of using this kind of wood. I have seen conflicting articles saying that it may be OK to use pressure treated wood after 2003 such as this one: Using Pressure Treated Wood For Raised Gardens...Is It Safe For Growing Food?? However, I am trying to replace my chemical habits with good non-toxic ones.

What type of wood will be good for a few raised veggie beds? About how long do you think it will last before needing to be replaced? I'm in zone 7B if that makes a rotting difference.

Answer 1

Cedar is the most commonly available rot resistant wood. There is another solution which lacks aesthetic qualities but adds years to the life of wood. Wood rots when it is constantly moist. Here's how to avoid this and use any wood you can get that is not treated:

• dig a trench about 3 inches wide and six inches deep around the perimeter of your bed.
• add two to three inches of 3/4 to 7/8 crushed gravel and tamp down
• start assembling your wooden raised bed
• on the side of the wood facing the soil line it with an impermeable layer. ( I happen to have some pond liner left over which does a great job but you can also use 40 - 60 mil plastic sheeting used for covering insulation. This plastic should last five years if covered.)
• place your wood and liner in the trench, back fill with soil and you are done

Other materials to replace wood include stone, used paving stones even empty wine bottles!

Edit Jojo has commented that liner may not be food safe. Roofing liner and swimming pool liner are not food safe. However Firestone's product page shows numerous places where it is used for food production and I cannot find any literature or studies disproving their claims of food safety.

Firestone's Building Products

Answer 2

@kevinsky's answer is very good if you want to keep edged raised beds.

Another thing to consider is that "raised beds" don't need any kind of edge. They're mainly for aesthetics -- which might be important to you, but aren't necessary for the plants. Unless you have a need for very high beds, you can simply mound up the soil. My garden doesn't have edges around the beds. Every spring I rake some of the soil from the paths and mound up the beds. The paths get compressed by foot traffic, but we never walk on the beds so they stay raised.

I've seen people use regular untreated lumber (i.e. spruce/pine/fir) for raised beds. It lasts 3-4 years. If you are anywhere near a real lumberyard (not a big box store) or sawmill and you can get cheap, rough-cut, possibly second-quality boards, and you don't mind rebuilding beds every few years, it may be cost effective to just build with this. (Use @kevinsky's drainage tips to extend the life.) Since they're natural and untreated, when they start to rot and need to be replaced, you can break up the boards and bury them under your raised beds. They will compost slowly over the course of several years -- no waste!

Answer 3

Check out juniper! It lasts longer than cedar or redwood without any chemicals, plus it is an invasive species in Oregon. Cutting it helps to restore the grassland ecosystem -- no old growth forests need be clear cut to obtain this stuff!

Answer 4

Constructed 3 large raised containers 5 years ago using green oak and have found this to be a successful material. I was looking for a very solid and long lasting material. The raised boxes are 4' x 10' x 2', using 2" thick cut material. A few problems I found with green oak included the weight and the density of the wood. So make sure you have access to a good pick-up truck available and a well built assistant. Another important necessity will be good tools, because you will not be able to securely sink a nail into this material. If you want to use nails, you will first need to drive a screw with a smaller diameter than your nails into the wood then remove the screw and sink your nails. Needless to say we went with screws and make sure you use a fully charged power screwdriver. I built these 3 boxes for approx. $300. .

Answer 5

I build my raised beds out of 2x12x8 boards of Douglas Fir framing boards. They will last over a decade. I live in Oklahoma, zone 6. Do not use treated wood for edible gardening - unless your consumers can tolerate arsenic and cyanide in their diets!

Answer 6

Just to add a few notes about my experiences:

Southern yellow pine lasted 3 years. SYP with linseed oil applied the first year added another year to its life, maybe.

This year I built cedar boxes similar to how Ana White did them here. Though mine were 50% more expensive each. Still not bad.

I have 30 or so Black Locust logs 8-10' long 3-15" in diameter some of which I'll be building some "Lincoln Log" style beds this year as an experiment. Black Locust is quite rot resistant and makes great posts.

Douglas Fir is better than SYP. A box I made from DF was good for 5 years or so.

Answer 7

Cedar, redwood, brick, cinder block. There are limitless options. The keys are durability (rot-resistance) and safety (won't leach poisons)

Answer 8

Here in the rural northeast, rough-sawn hemlock is a popular choice. Cedar is also a good choice as is redwood. Try to get heart-wood if possible. I have had garden boxes out (with ground contact) for one season and can see the dry-rot starting on a few of them. Isolating the wood from ground contact is important and the gravel idea outlined above looks like a good one although, if you aren't in a really wet area, maybe just putting the beds up on a few flat rocks, like what is used for a stepping-stone path would help, too.

Answer 9

Cypress hasn't been mentioned so I thought I'd throw that out there. It has very good decay and insect resistance.

Cypress has the approval of Burton Guster II.

Henry Spencer: So what kind of wood are we gonna use for these bookshelves, Gus?
Burton 'Gus' Guster: Uhhh... cypress.
Shawn Spencer: Cypress? Really?
Burton 'Gus' Guster: It's a good wood. It's what Noah's Ark was made of.

:)

It's also the wood that is currently being used to make raised garden bed kits sold by Square Foot Gardening.

You may also want to look into concrete block. Smaller blocks such as 4x8x16 seem to be the right size as do some of the concrete edging. Cost per linear foot is cheaper than the expensive, naturally decay resistant wood and it lasts a lot longer. Cons are it's a little harder to install properly it might not be as pretty depending on your tastes, skill level and ultimate design.

There are some concerns about using concrete due to the additives. I've read conflicting information on the subject so I encourage you to do a search and come to your own conclusion if you use cement blocks.

Answer 10

I wanted to use cedar but didn't want to pay the premium. I found a good article about using cedar pickets, so I built mine like this: $10 Cedar Raised Garden Beds.

Answer 11

Here is some useful info for you. I've been using a product called the eco wood treatment for years and it is amazing. It is a wood preservative that is completely non toxic and suitable for use with garden soil contact. The stuff turns wood a nice aged gray patina. It's a great way to may cheap wood like pine last years and years longer than it would otherwise. This is my secret! You only have to apply it once. I use it on my deck and outdoor furniture etc. Look it up, it is amazing stuff.

Answer 12

You could also use stacked cinder blocks if you don't want to worry about the wood rotting away. Plus you get extra pockets for plants on the side if you stack the cinder blocks with the holes up.

Answer 13

permanent raised beds without structure]11]]2[2 year old beds out of pumice soil in a lodgepole jack pine association]3]3

Concrete leaches lime into the soil around it raising the pH. Which might be a good thing depending on where you live. You should know your pH of your soil, the ideal pH of each type of plant you plan to grow and how to manipulate it up or down in tiny increments.

I was surprised no one mentioned 'TREKS'...I think that is the correct spelling...it is made out of recycled plastic jugs, never rots. Comes in lots of colors but I always use dove gray as that is the natural color of exposed wood. Great for edging gravel walkways and decks, too. Easy to bend when warm (use a propane torch carefully if the weather is cool). It isn't as cheap as wood or cinderblock but you won't have to line it. Saw it like wood. You will need a drill bit to drill holes for your screws.

And you really don't need sides like one of your earlier answers. I double dig my beds once at the beginning and never do it again. I always have a trench at the bottom of my beds to direct extra water away from walkways and the beds to prevent erosion. I do retrench once a year (looks so nice) throwing the soil on top of my beds, use a green cover crop every winter and topdress after planting with a decomposed organic mulch. The soil organisms eat the mulch, go back down into the soil and poop it out doing the mixing and aerating for you!

After double digging your beds, you'll see at least 2-4' of bed height. I make my beds 3' wide with walkways on at least one side. Rake the top so that it is level then I use a big piece of plywood, lay it on top, get up on it and jump up and down to firm the soil to a proper density. By now your beds will be 1 1/2' to 2' in height. They will reduce a little more depending on the amount of organic matter that originally came with your topsoil and/or the decomposed organic matter you mix in while double digging.

I never waste an inch of my beds...no straight single rows for me. I broadcast my salad bowl seeds, after soaking peas and beans I arrange them all over the top about 3" apart and push them lightly into the soil and I stagger my corn, tomatoes, potatoes making triangles with equal sides. For the seeds I'll use a rake and standing on one side of my bed to reach the opposite slope, I lightly rake up the sides and flip soil on top of my seeds. You'll have plenty of practice while forming your beds and develop confidence you'll not bury your seeds too deeply. Just pay attention to the directions on the seed packet or twice the thickness of your seed should be the depth...shoot, I think that ratio is correct.

Then I take my rock rake the heavier one with study metal tines, turn it up on its head and tamp down the soil over my seeds. Seeds need to have proper contact with the soil...just don't overdo the tamping thing, and maybe a bit more gentle over your soaked seeds. Careful with fertilizer until you get sturdy plants. And don't forget the sides! I plant strawberries or other low-growing plants there...the north side is a good place for a second round of peas in the summer and the south side make sure the plants don't shade the rest of the bed. I also make big square beds...6'X6' (3' is the maximum comfortable distance from the walkway...) with walkways on each side for peas or corn...or squash and pumpkins.

Keep an eye out for disease and insects and critters of course. I plant densely all the time. I thin and prune to allow for as much ventilation as I can. I have fans in my greenhouse and I'll even use them outside if it is humid and windless. Remove any decaying material and remove spent plants after harvesting. Put in your compost heap.

Make sure you get your soil tested otherwise you'll be guessing at whatever you add to the soil. Then get to know the signs/symptoms in your plants of deficiency AND excess nutrients. I like to use a cheap oscillating sprinkler to water my garden, make sure the moisture gets 6" deep in your soil (hand water with a soaker while seedlings...have to keep the top of the soil with your seeds moist, not wet until they are established...then you train them by watering deeply and allowing to dry out before watering again).

Don't forget to put your beds away for the winter by growing a green cover crop. In early spring turn those plants into the soil. It feeds the soil and greatly reduces weeds!

Oh, the salad bowl thing...I take all my seeds of lettuce, spinach, radishes, carrots mix them in a spice jar with holes on the top and cover the top of the salad bowl bed...thinly. You'll love this...The first to come up are radishes, you eat those and it leaves more room for the lettuces which as you eat those you are thinning. When you get through the season and there's plenty of room for all the plants just cut leaves off your lettuces instead of pulling the whole plant. Michael Dirr taught me how to do this...He is my garden guru, grin!

This is a picture of my beds in this environment...ugh at least a 3 zone. Colder and more unpredictable than Alaska, sigh. This is how I prepare ALL of my garden beds. One time only.