What should go under a raised bed that is on top of tilled dirt?

Question

I am making some raised beds for my garden. What would be best to lay at the bottom? Would newspaper, rocks, stuff of that sort work the best?

This will be put directly onto tilled dirt.

Answer 1

I would recommend having 24" of soil for your roots to work with. I would not put anything that roots cannot get through (e.g. rocks) in the top 24 inches which would make it harder for roots to get through. Every year I would recommend turning over the top 2 feet of soil so that it is loose for roots to freely grow and to mix the nutrients. Other than that, enjoy the new raised beds. Sounds very exciting!

Answer 2

You can put anything non-toxic - including when it breaks down - under your raised bed.. or you can put rocks. I have gardened and farmed organically for over 30 years and have put in many raised beds. If you wanted to raise a low area or just make a deeper bed, you could use good dirt. I have gotten potting soil on sale for as little as $1/40-lb bag and used that. With a deeper bed, you can rotate crops that make deep roots, or you can make permanent plantings of deep-rooted crops that you don't want to spread, such as horseradish or comfrey. Hope this helps!

Answer 3

Probably the only important thing you can put down is hardware cloth if you suffer from voles. Otherwise the several inches of dirt usually does the trick to keep anything underneath growing.

Answer 4

Raised beds made from lumber are to be treated just like pots. USE just sterilized potting soil that has mychorrhizae and bacteria incorporated. Do not use GARDEN soil. Do NOT USE rock, gravel...perhaps landscape fabric but voles and moles and shrews are just not a big deal. Drainage is. If you use gravel/rocks you actually make a perched water table which means the drainage has been compromised, big time. I've actually suggested use of old nylons if loss of soil on a deck is a problem and it seems to slow the drainage down as well. MAKE SURE that you use sterilized potting soil, I kid you not. Garden soil is a big no no and if you want the entire why not I can explain and/or find on this site. Plants that aren't planted in the garden need all the help they can get and that means great draining soil, no pathogens that have no biological controls...do not use garden soil!

Treated lumber especially railroad ties are full of super toxins...as long as you do not EAT your crops fine. But otherwise, gross.

If you are worried about weeds...just pull them out or use a mulch without weed seeds such as human poo poo decomposed mulch. Super stuff but not recommended for edible crops...heavy metals. Ornamentals and plant beds are thrilled to have this stuff if you can find a resource! Never ever ever ever use landscape fabric for weeds. Stops the entire process between organics, decomposed organics and the micro and macro organisms required for health of the plants. Bad idea. They say it is 'weed fabric' to get uninformed people to buy it and use it...horrible idea! The only reason for this stuff is to put beneath gravel so that the 'fines' don't percolate back up through the coarser stuff...so you can watch your gravel go bye bye and needing to be replaced.

Do not use pressure treated nor the railroad ties for any edible plants! Use pressure treated lumber that is lined with plastic except allowing for big holes for drainage. Plants in pots or these kinds of raised beds are susceptible to root cold damage.

What are you growing, why do you need raised beds...I've got much better ideas and how to keep plants in pots alive through winter, if you have gnarly winters?

Excellent question by the way!!

Answer 5

You haven't mentioned why you're creating raised beds on tilled earth so I'm going to assume it's aesthetic reasons rather then necessity due to a compacted base, or drainage issues. Since the manufacturer of copper compound pressure treated timber doesn't recommend laying directly against vegetable garden soils, you're going to need to put a layer of plastic to protect the soil. On the other hand, other experts say the plants are more likely to die from copper poisoning before we do!

Since your raised bed is only 8 inches high, you have the alternative of not using the timber, and just use rounded edges. Eventually it will hold itself in place as the soil web rebuilds, and without the timber there, you don't give a place for snails/slugs to hide during the day. You also increase the surface area for planting.

As you've seen, there are many opinions on how to create a raised bed. Since the earth has been tilled, I'm presuming it's now loose, but you could loosen it further using a spading fork to a depth of 16 inches so that your total depth of uncompacted soil is going to be 2 feet.

If you have straw readily available, one of the easiest things you can do is to create a no-dig garden. In your case you can just layer down manure and compost, and lucerne straw, and then water it in. No-dig gardening attempts to replicate the way that nature creates the soils that give rise to the forests etc. All the digging is done by earth worms for you ( or deep rooted crops ).