I think your plan is wrong. No gravel, fill the beds with “container potting mix”, in my area, $50/ yard (in April 2020), in bulk.

bad tree roots will grow up into the fresh new soil.. about as fast as you can shovel it in ...

especially since you probably cut most of them.. to dig out the old soil .. and at those cuts.. the tree will respond by growing more feeder roots ... right into the new soil ...

im thinking at best.. you are only buying a couple years.. before you are right back to where you started ...

perhaps a pic or 3.. will help us brainstorm for you ...

ken

Ken, did you miss the part of raised beds? I think the OP wants to fill a 10-12” deep raised bed

Tree roots will still grow up into a raised bed.

if you must have hostas in that particular area, you should consider putting them in nice big pots and then put them under the tree(s),

newhostalady..we built stone edging in some sloped areas..in a couple of spots the stones are stacked 2 stones high..my "raised beds" aren't as deep as what you're considering..all I did is plant slightly high and add my homemade compost..no purchased soil or products..I wouldn't use gravel..from what I've read gravel creates perched water tables..I know you battle tree roots..I'm not sure if this is your situation but I'd be concerned about building a deep raised bed surrounding mature trees..raising the grade can kill trees..eventually..

Maybe I did not understand, I think of a raised bed as a box made from wood. Either open bottom, or a wood bottom.

A “coffin”

Before I answer comments, let me give you some pictures. I think that will help to understand my situation.

And Jim, my husband built a large wooden container to plant in. I found out that a closed bottom box was now a container and had to have container soil in it. I have loads of containers. It's a lot of work. I gave up on the wooden container. It now remained emply. There is a wooden platform that is put on top of it. I put pots on top of it now. That's all.

If you put a raised bed there it will need a back and it will need to be away from the fence. If you build directly against the fence the wood will rot.

Personally, I wouldn’t do the raised bed. It’s a lot of work and I don’t think it would improve the look of that bed. You have several attractive and healthy plants, so I’d just duplicate the things you’ve found have worked.

newhostalady..ahhh..your trees aren't "in" the bed..I don't have any circumstances like yours to be able to offer advice..I agree that pots are more work..my inground hostas are easier than my pots..

Jim Mat..most people DO have raised beds built with wood walls..I have slightly "raised beds" with stones or logs..and not even fully enclosed..just a barrier on the low side that retains just a little soil so the plants are slightly high..

Newhostalady, I don’t have any advice about a raised bed. But I have to say that I love what you have done with some of the vertical planting along the fence. Tree roots are really tough to deal with, I know. In the front yard, I have a large Crimson King Red Maple. I am constantly fighting roots too. I just wanted to say, what you are doing in the yard looks lovely!! 👍🏽

debra

OK, in my area the OP would like help with a planting bed or area that may be raised using retaining walls. But it not called a raised bed(in my area).

Your existing soil may have different needs than my soil or some

where else. I recommend consulting locally. If you want this sites help, often the pros would recommend a soil test.

Is this DIY or are you contracting this out?

Ken, I know that tree roots will grow into the new bed. What I don't know right now is how many roots we will find and how big the roots there are. I am so tired of battling tree roots and poor drainage. I may still use spin out bags on the hosta placed there. In fact I have some spin out material that I could line the bed with. That would buy me more time.

I have learned that tree roots don't extend evenly around the tree. So it will be interesting to see what roots are there. We would have to decide how many to remove depending on the size.

Nicholsworth, I am aware that placing soil on tree roots can affect the tree. In turn, this tree affects my life, my home and the value of my property. My city does not support property owners when it comes to trees, and I can't fight the city. Trees are important. But please, trees grow and a tree that wasn't a problem decades ago, could become a problem later on. Here you can make a special appeal to have your tree removed. The city squashes it, after you have had to pay hundreds of dollars just for the application process.

floral_uk, the back of the bed would be the retaining wall. Here is a closeup so you can see that the bed would not be against the fence.

What fun would there be in gardening if you just plant what seems to grow in that area?

Jim, my husband will be doing the work. The stone for the front of the bed are on the retaining wall in one of the pictures.

Thanks for your kind words Debra!

Gardengal, my concern is that I will only have about 50 percent of the original soil to fill the bed with. Any hard clay will not be used. So I don't know what to use for the other half of the soil.

You can purchased bagged topsoil or even dedicated raised bed soil. If you need a lot it will be cheaper to go with a bulk soil product, in which case any 'garden planting mix' will work perfectly well.

newhostalady..of course you know not to bury trees..it was just a friendly reminder..my trees have more ground..I still have space to plant lots of plants..I remember your efforts with the city for permission to remove your tree 😥..could you call a nursery in your area for soil amendment suggestions?..

Lining the bed with spinout fabric would buy you some time. At least it will slow the roots down. I've had good luck filling the bottom half of oversized pots with pine bark nuggets and bagged garden soil on top. Maybe undyed wood mulch would work as a substitute .

The AHS just did a zoom class and the teacher suggested sinking two plastic pots, one inside the other. She said to go for a snug fit. Then once or twice a year lift the inner pot and cut off any tree roots. You can tape landscape fabric over the bottoms of the pots to keep the roots out longer. The rim of the bottom pot should be at soil level if you want to leave them out all winter.

Maybe combining a raised bed and double potting would solve your problem.

Look into this

https://www.permaculture.co.uk/articles/many-benefits-hugelkultur

We’ve raised our soil level with a lot of top soil which includes 25% humus, peat, etc. it’s rich and great for planting we usually put down 12 inches or more. We have horrible clay soil so it’s necessary. We unfortunately planted a red maple in the front yard. Tree roots now are a major problem. We started using plastic pots Inside spin out bags. Turn the bags inside out and put the pots in them. Fill the pot with rich planting soil and the plant. they work well. I will take a pic and post later.

When I added an 18" stacked stone wall bed, I filled it with a mix of compost, peat moss (because I already had some), some leftover coco coir, some bark fines, and Whitney Farms Raised Bed soil. Stuff smells like crap, literally. It must be good!

For my 2' wooden raised bed which has no bottom, I also used Whitney Farms. I love the stuff. I used it in all my new garden beds to supplement the crap clay. Then top with mulch.

We have a nursery nearby. I can go and check out what they have and what they suggest. I just wanted to have some input and ideas before I ask them. This season with covid-19 everything is different. Availability of soil and amendments aren't necessarily available as they usually are at this time.

I had heard of double potting Madplanter. I thought of giving it a try but haven't been able to find the right sized container. As I recall, I believe the inner pot should have drainage holes on the sides and the bottom pot should have drainage holes on the bottom. The holes of each container having drainage holes in different areas,
Single pots buried into the ground don't usually work because roots find the drainage holes and enter. But I have one pot that has thrived in the same buried pot for three years!

Lindalana, that is interesting.

Miles, unfortunately, we planted a birch tree in our front yard. Yikes, the tree roots are terrible! I've always worried about putting a pot into a spin out bag. Does water drain properly? A picture would be great.

It's been slow going making our new bed. Took out the last plant a couple of days ago. I really like this undulata albomarginata. I've been eliminating some hosta that are not favorites. This variety I will keep.

The stone you see in the picture will be the same stone for the front of the new bed.

Full of tree roots!

It took a long time to remove the tree roots.

I realized that the roots are way too short for a plant that has been growing in the same location for so many years. Some crown rot too. Very poor drainage, as I suspected,. Ends of roots rotted off. Hopefully the new bed will greatly improve the drainage problem.

I don't know if you can see it, but the maple tree has very fine roots that entangle and weave through the roots of other plants. That makes sure that the tree gets their water first and also makes it difficult for the hosta's new roots to get through.

Look at this bit of tree root.

It's almost as tough as wire!

Two undulatas ready for potting.

So the raised bed is almost done! We didn't have to cut any major roots on the bottom of it. My husband put some gravel below the raised bed and in front of the bed to allow for drainage. Drainage has been a problem in that area. Lined the bed with spinout fabric I bought a couple of years ago and it was a perfect fit.

Sorry, I thought I had a picture to post, but I don't. I can get one tomorrow.

My question: I think the soil is going to take time to settle. In the meantime, I want to get going on planting there. Should I plant the hosta crowns slightly above soil level and then mound up the soil? I don't want to have to dig the plants up next year because they have sunk down.

Here's the picture. Now how to decide which plants will go there.

It’s a really good looking bed newhostalady! I am not great myself with these decisions about planting.......maybe plant crowns close to the top and cover. From what I understand, it’s better for the crown to be closer to the top then buried. Something I have been guilty of! :-)

debra

You're probably right---plant crowns close to the top and cover. I'm just overthinking it. Also, probably procrastinating because I am not sure what I will plant there!

Right now I am thinking about putting my Touch of Class on the left, then maybe First Frost, then my Hakonechloa grass, one more hosta and then Robert Frost. We'll see.

Those all sound good in that order!

debra

Just about done.

What an excellent project, nhl! It’s sophisticated looking and the shelves for pots look great with your new raised bed. Congratulations on such a success!

Ditto that! You must be thrilled with it and I am sure your watch owl appreciates it's perch too.

Thanks kathy and peren.all. Peren.all the owl is looking out for squirrels that are trying to dig in that bed!

I am looking forward to seeing the plants that are planted there next year. I've added a few minis, an arum italicum, a few propagated heuchera and am planning to replant tulip bulbs that had to be dug up. I don't have much success with tulips around here (even though I love them)---the squirrels love them too! An avid gardener I know told me she puts chicken wire on the soil where she plants bulbs to keep the squirrels from digging up her bulbs. But even then, the squirrels sometimes just bite off the bud. Frustrating---when all I am asking for is a dozen red tulips!

Photo taken April 2018. One of those rare years when I actually got to see all my tulips bloom. This year---not even one. (Note, that hachone grass behind the tulips is the one in the raised bed now.) I love that plant! Mine doesn't get the amount of sun it should, so the coloration is not at its best. Love seeing it sway in the wind.

Yes, it all looks lovely. It is just right in ratio of plants and negative space.

newhostalady..your new raised bed looks so nice!..your garden is so tidy!..I try but I can't catch up..squirrels are a big problem for me..tulips are beautiful but I've never planted any here..I was afraid I'd be disappointed..my crocuses weren't what I hoped..