Hello, I have built raised garden beds in my backyard. They are about 24 inches high (pretty tall). I need to fill the first 6 inches with something lightweight that won't put a lot of pressure on the bottom of the beds over time. The boxes are built out of cedar fence pickets. The recommended fill depth for the soil I am getting is 18 inches max, after which the soil risks becoming anaerobic. I live in Austin, TX.

Question :1 - Should I line the inside of the garden box with anything to keep the dirt inside the boxes + keep moisture in? If so, what should I use?

Question 2: What should I fill the first 6 inches with? Leaves and twigs? Scrap wood? I have some fill dirt that I can use, but I'm worried that it will crack the garden beds over time.

Thanks in advance :)

For #2 I filled ours with as much cardboard, tree trunks, twigs, packed leaves, anything I could find. Advice, if you do this I would wet everything down after dumping whatever you have, let it sit and find more stuff to layer in, rinse and repeat until your soil fill line.

Prior to garden
The thread "Thoughts on HardiSoffit raised bed" in All Things Gardening forum

Afterwards
https://garden.org/pics/2017-0...
https://garden.org/pics/2017-0...
https://garden.org/pics/2017-0...

Your new beds are beautiful.

I line my raised beds with two layers of good quality landscape fabric to keep the planting medium from escaping. I like the Preen brand available at Sam's club. The landscape fabric also serves to prevent weeds and roots from finding their way into the bed from underneath.

For the deeper of my raised beds I added sticks and twigs that had fallen in the yard, plus some pine cones and Spanish moss before I added any planting medium.

Awesome, thanks for the tips. I've seen some articles on Hugelkultur. I have access to a bunch of Pecan Wood that I can use to line the first foot or so of my beds. Would you guys think that's a good idea? Any reasons why it wouldn't be?

If you want something lightweight that won't break down over time, use styrofoam. The large pieces that come with packaged electronics like TV's etc are great. You can fill in the bottom of the beds as much as you can with that, then put the landscape fabric over top of it. It will be there forever. Try Best Buy or other big box stores, they'll probably give you all you need.

Using sticks, wood, fill dirt, leaves - all that will break down anaerobically and stink and rot down there in the bottom of the boxes. Wood under the soil will also attract termites, potentially, with possible bad results for the support structure of your beds in the long term.

Your soil is going to settle anyway, and putting stuff in there that's going to rot will just cause you to have to fill in more dirt down the road.

Anthocar - I think the hugel approach is ideal. Increases the soil life as well. You could line the bottom of the boxes with cardboard and then start filling it up with branches and twigs. Once you get to a certain level, you'll need to focus on your growing medium.

FYI, to help clarify my end goal and why I built the garden in the first place: I plan on doing organic gardening and my end goal is the most nutrient dense foods possible.

dyzzypyxxy, thanks for the tip. Won't I have to worry about bad drainage if I do it this way? Pros I can see to doing something with styrofoam is that the roots wont go beyond the prime soil that I'm spending $$$$$$ money on. Cons are that drainage might be bad. If I filled it, I wouldn't do sticks and twigs per-se. I have access to the pecan wood (in the picture below) for free so it would mostly all be logs. I'm actively composting now (and composting a lot) so filling in with more soil later doesnt bother me. A stinky garden would though. Knowing this, you think it would still smell bad if the logs are all i use to line the beds? You still think styrofoam is the way to go?

Shadegardener - Same questions about drainage. Won't cardboard inhibit drainage?

greene said:Your new beds are beautiful.

I line my raised beds with two layers of good quality landscape fabric to keep the planting medium from escaping. I like the Preen brand available at Sam's club. The landscape fabric also serves to prevent weeds and roots from finding their way into the bed from underneath.

For the deeper of my raised beds I added sticks and twigs that had fallen in the yard, plus some pine cones and Spanish moss before I added any planting medium.

This is awesome, thanks for answering my question

If you have no qualms about what the raised beds are sitting on, then you can forego the cardboard. If you are trying to go organic, then please study up on Preen. Two types - one for vegetables is considered "organic" in that it's pure corn gluten meal. The other for flower beds is not. There are also some warning labels on Preen so read them carefully. Sowing seeds in a bed treated with Preen may be problematic. If you're wanting to go organic all the way, I don't think the corn gluten meal in Preen comes from organic corn. Personally, I don't think weeds in your raised beds are going to be that much of an issue that hand-pulling can't take care of.

If you use pieces of styrofoam, they will have cracks and spaces in between the pieces that allow water to drain through. You won't be able to find solid pieces that would "seal" the lower parts of your boxes.

I suggested the styrofoam because you said you wanted something lightweight to fill up the bottom of the planter boxes. The wood might work great. I really have no idea, except that it surely will eventually break down and then you will have soil all the way to the bottom of the boxes, putting the weight against the bottom boards.

To make your soil "lighter" I would add perlite to your compost.

Another idea. I have tall pots that hold a lot of soil. The annuals I plant in them don't need all of that soil to grow in and it makes them heavy to move. I use plastic coffee cans with lids on them to take up space in the bottom of the pots. Might make a more practical "filler" than styrofoam peanuts. Styrofoam does have some issues under certain conditions with releasing styrene - not a good thing.

No, not peanuts, Cindy. The big blocks and pieces used to package fragile items.

Styrofoam is mostly air, which is what makes it so light. The styrene released, if any, is miniscule - experiments done with styrofoam have not revealed even measurable amounts. It is approved for food storage, too. (had leftovers from a restaurant to bring home lately?) In this case, it would not be released into the soil since the styrofoam would be below the soil. Not that much air circulation, and water percolating downwards would tend to "wash" it out the bottom, not into the box.

Ah - misspoke when I said "peanuts" instead of "blocks".

If you are considering the Styrofoam as just something to take up space, maybe consider what we did one year. We saved a ton of aluminum drink cans and lined them in the bottom of containers with the hole in the can facing downward. Two layers tightly packed took up plenty of room, allowed drainage, saved us from the expense of extra planting medium and, when we took the container apart this winter we were able to wash the cans and put them into the recycle bin. It was a win-win situation.

anthocar said:Hello, I have built raised garden beds in my backyard. They are about 24 inches high (pretty tall). I need to fill the first 6 inches with something lightweight that won't put a lot of pressure on the bottom of the beds over time. The boxes are built out of cedar fence pickets. The recommended fill depth for the soil I am getting is 18 inches max, after which the soil risks becoming anaerobic. I live in Austin, TX.

Question :1 - Should I line the inside of the garden box with anything to keep the dirt inside the boxes + keep moisture in? If so, what should I use?

Question 2: What should I fill the first 6 inches with? Leaves and twigs? Scrap wood? I have some fill dirt that I can use, but I'm worried that it will crack the garden beds over time.

Thanks in advance :)

I personally would worry a lot less about drainage, and more about keeping the soil moist.
In the deep south, with little rain, keeping containers from drying completely out, and unable to absorb moisture.... It's a big deal.

Anaerobic?
I totally wouldn't worry about that either... One of those problems of gumbo clay and constant rainfall....
planning to fill those things with gumbo?
Surely not.

So....
How wide are those boxes?
I think Ida built them twice as wide....
more room for veggies, and easier to keep watered.

As far as what to put in the bottom?
I'm with the people that want you to add material that will feed the plants.... Either the limbs and leaves idea or just regular soil.

If you are worried about the bottoms blowing out.... Maybe reinforce them with 2 x 4s or whatever, and decking screws.

Personally, I wouldn't worry about that.
You can always replace the bottom boards later.... Or not.... The box will still work after the bottom boards bust loose.... I useta make raised beds with no supporting materials... Just the clay....

Good point about trying to keep them moist. I've read that once sufficiently rotten, the logs act as sponges for moisture in the bottom of the boxes. If I do use the pecan logs, would you worry about termites like someone mentioned here? What about stinky rotted wood as the wood rots later on?

As for bottom boards...I'm talking about the lowest boards on the sides of the bed, there are not actually any wooden boards in the bottom of the beds.

And they re 25 inches wide

stone said:
I personally would worry a lot less about drainage, and more about keeping the soil moist.
In the deep south, with little rain, keeping containers from drying completely out, and unable to absorb moisture.... It's a big deal.

Anaerobic?
I totally wouldn't worry about that either... One of those problems of gumbo clay and constant rainfall....
planning to fill those things with gumbo?
Surely not.

So....
How wide are those boxes?
I think Ida built them twice as wide....
more room for veggies, and easier to keep watered.

As far as what to put in the bottom?
I'm with the people that want you to add material that will feed the plants.... Either the limbs and leaves idea or just regular soil.

If you are worried about the bottoms blowing out.... Maybe reinforce them with 2 x 4s or whatever, and decking screws.

Personally, I wouldn't worry about that.
You can always replace the bottom boards later.... Or not.... The box will still work after the bottom boards bust loose.... I useta make raised beds with no supporting materials... Just the clay....

Nor was I talking about boards under the soil....
Bottom boards = boards across the bottom of the wall.

Cedar shouldn't be attractive to termites.

Stinky rotted wood.... I've seen stinky wood in anaerobic conditions....

Rotted wood buried in the soil..... Really shouldn't be stinky.... And even if it were, it's buried... Who's gonna smell it?

So.... You didn't answer the question about width. You said they were 2 ft tall, but nuthin about width.....

It's at the very bottom of my post ;) 25 inches wide x 93 inches long x 25 inches deep

Thanks for the input about the stinky wood. With regard to termites, the wood I brought home turned out to be oak, not pecan. The beds themselves are cedar and I'mglad termites don't like Cedar. Even if I have or get termites in the oak, will they eat veggies?

Here are the logs I'm going to use for the bottom floor of the garden (attached)

Thank you everyone for all of the help and input!! Really helping out a first time gardener!!

Still open to any tips you may have for me :)

stone said:Nor was I talking about boards under the soil....
Bottom boards = boards across the bottom of the wall.

Cedar shouldn't be attractive to termites.

Stinky rotted wood.... I've seen stinky wood in anaerobic conditions....

Rotted wood buried in the soil..... Really shouldn't be stinky.... And even if it were, it's buried... Who's gonna smell it?

So.... You didn't answer the question about width. You said they were 2 ft tall, but nuthin about width.....

anthocar said:It's at the very bottom of my post ;) 25 inches wide x 93 inches long x 25 inches deep

Thanks for the input about the stinky wood. With regard to termites, the wood I brought home turned out to be oak, not pecan. The beds themselves are cedar and I'mglad termites don't like Cedar. Even if I have or get termites in the oak, will they eat veggies?

Ok, thanks....
Sorry I missed seeing the dimensions.
I usually like 4 foot width, reach from both sides, and the extra width means 2 rows of vegetables in the bed.

The only time I've ever had trouble with termites in the garden.... I brought home several truckloads of sawdust from a lumber reclamation center... Tried using them as mulch....

The termites ate a few of my cantelope.

I would use sawdust again, if I could lay hands on it.... So.... Yeah.... Termites are not a big issue.