Gardening: Trees in a raised flower bed?

I’m building a raised bed in my backyard.

Here’s the deal…

  • Section 1 will be an area where I dug out grass and am laying down some dirt, some topsoil and some mulch. A total of 8 inches.
  • Section 2 has my grapevine (one main vine) and a small cherry tree.
  • Section 3 has a new little lilac bush. Right now it’s just a budding twig.

Sections 2 and 3 have mulch on them already, about 3" worth (mulch made from my old apple trees and a chipper). The cherry tree and the grapevine were there when I threw the mulch down, so they were originally planted in the ground beneath.

The lilac bush is new since the mulch, but I do think we dug up some ground when we planted it.

So what I intend to do is add about 4 or 5 inches of dirt and mulch on top of the existing mulch in which the tree, grapevine and lilac bush already exist.

Is this going to be too much mulch and soil at the base of an already-established tree and grapevine? I’ve heard that you can over-mulch a tree.

Should I dig up the lilac bush (twig) so that it’s not drowning in mulch?

My ultimate goal is to have a nice uniform raised bed on that side of the yard so I can plop in a few annuals and so I don’t have to mow around all that junk. And to keep the dog out. But that requires 8" of materials all the way down.

Any opinions?

I have no experience with mulching actual trees, but I’m here to tell you that a lilac bush pretty much doesn’t care what you pile on top of it–it’ll just send up more suckers through the mulch. It’s hard to kill a lilac, and I’ve never heard of anyone doing it with 8" of mulch and soil. The lilac will just shrug and adjust to the new soil level.

I’m also here to tell you that a lilac twig, in a few years, is going to be a dooryard bush, the kind that New England poets rhapsodize about. It’s going to have a diameter of at least 20 sprawling feet, will be producing dense shade underneath it, and is most definitely not suitable for residence in a flower bed where you’re hoping to “plop in a few annuals”.

And lilac bushes, as noted, put out suckers. I planted mine in 1990 as a forlorn little twig from the garden center, and today it not only takes up the entire corner of the back yard, but has spread to my neighbor lady’s backyard too, under her redwood privacy fence. It’s not going to stay confined to your tidy little flowerbed, and it’s going to have lilac branches arching way out over the lawn and swatting you in the face every time you try to get in there and edge your flowerbed.

Nothing is going to grow underneath it except small, tough things like American weed violets (not picturesque fragrant violets). And you can’t put hostas and things under them because a lilac is a dense mass of suckers coming up, which it requires to renew itself every year. You can’t prune a lilac to look like a tree and have it survive for more than a few years.

Any shoots that do come up in the yard will be snipped off by the mower, but then since you aren’t allowing it to renew itself from suckers, it’ll eventually simply disappear.

All in all, I’d re-think making a lilac a part of a flowerbed. Lilacs are made for those awkward corners you can’t do anything else with, not for your prime-time space.

ETA: See this picture here? That’s how big and bushy it’s gonna be in 10 years.

Hmmm…this twig is a sucker from one of the other 2 lilac bushes in my yard (no idea how old) which have so far contained themselves nicely in the flower beds they’re in (I did not build said beds).

Also, my neighbor’s lilac shades over part of Section 1. I haven’t had any problems with his throwing suckers into my yard.

My new twiggy one is way at the end, and I don’t plan on having any annuals over there.

I think I’ll do ok with the lilacs. They sure beat the stupid blackberries that used to be in that space.