I own some ajuga. It seems relatively harmless but does spread in the grass.

My concerns with it under your tree are:

1 I have found it is not native to North America.

2 Heavily planting it could disturb the roots of your pin oak.

3 Your neighbors may expect you to somehow prevent ajuga and woodruff from spreading to their yard thus signing you up for a lifetime of labor if you are in a tight spot it grows well.

Hmmm, if I wanted to fill my yard with the stuff what to do.

I suppose you could round-up the yard in early spring soon as the grass is actively growing. Come back a week later and round up again. Then a third time. After another week mow the dead grass as low as you can and plant 100 or so plugs of ajuga and let them spread. Mine has.

Just don't go tilling up all the soil in your yard or buying the tree under six inches of new top soil. THAT would challenge your big trees.

Is sweet woodruff the same as Galium odoratum? I know nothing about this but saw pictures of its spiny balls. Are they soft or just not that big of a deal?

Good luck. Let us know how it goes.

The issue isn't hurting the trees. The issue is whether or not you want to spend the rest of your existence in this house with ajuga. It's very difficult to control and almost impossible to get rid of. If there is the possibility that later on you might want to do something more interesting with the space, I'd go for something more manageable.

BTW, what is under my pin oaks are shrubs. The trees are limbed up about 20 ft, and there is lots of room to play with underneath.

Oaks don't like to be watered? Really?

Second the caveats about the wisdom of the unknown Ajuga. Surely there are far better solutions by the dozens.

Dan

'Is sweet woodruff the same as Galium odoratum?' ..... Yes

'I know nothing about this but saw pictures of its spiny balls. Are they soft or just not that big of a deal?' .....The latter. The fruit are tiny ie smaller than 1/2 a match head.

most likely.. in the long run .. NOTHING will grow under the norway ... if a tree kills grass .. the most invasive weed in the world IMHO ... you arent going to win ...

i dont like ajuga .. its boring.. otherwise.. frankly.. anything you plant as a groundcover.. will escape ... it is kinda within the definition of a ground cover.. to cover ground.. dont you think ... the fact that it doesnt stop at the grass edge is not really in the definition ...

as for the oaks.. or any mature tree ... plant whatever you want ...

when you read of disturbing the soil under a tree.. and the harmful impact ... think bulldozer.. backhoe.. etc ... and the severing of a LOT of roots.. and bigs ones at that ..

i doubt ... that you will do any significant damage with a hand trowel and some plant plugs ... and if you hit a big root.. just move the hole a few inches ...

again .... i am with dan .. there are dozens.. if not hundreds of things better than ajuga.. IMHO ... and you might get more suggestions in the perennial forum.. since your tree question has been answered ..

ken

Thanks for the answers, everyone.

The groundcover spreading isn't really an issue. There is no grass in the area with the trees (and what grass there is elsewhere will be torn up for a garden in future years). The lot is above and below retaining walls, so they probably won't spread to neighbors.

Mad_gallica, i wondered what shrubs you grow under your pin oaks? I'm struggling with what shrubs I could plant under them and the dry shade they produce.

Yikes, what don't I have under those trees.

Species roses, viburnums, trees peonies, hydrangeas, forsythia, mock orange, flowering quince, spirea, lilacs, clematis, fothergilla, bottlebrush buckeye - I think that's it. Then there are the perennials. The groundcovers are daylilies and pachysandra, then there are the hellebores, ferns, some wild gingers, and bulbs. The iris bed isn't under the dripline of one of the trees, but is in the root area.

I can't say that I've found the area under those trees to be particularly dry. Dry is what is under the white pines, where the branches act as permanent umbrellas, and the tree roots instantly grab anything that manages to make its way through that barrier. It also isn't particularly shady, given that there is plenty of space for sunlight to get in under the canopy.

I've also got ajuga, azaleas,bleeding heart, ferns, brunnera under my pin oak. I supplement water in summer. I've wondered if that is bad for the tree though.They are tolerant of wet soil, so I think it's okay.

"The groundcover spreading isn't really an issue."

Ajuga reptans (common ajuga) is an invasive pest plant in your area, so spreading probably is an issue. Retaining walls don't stop seed spread. It may not be quite as much of an environmental threat as some other species, but the fact that it's invasive (scientifically speaking, not just aggressive) is yet another reason to find a better option.

mad_gallica, you said:

"It also isn't particularly shady, given that there is plenty of space for sunlight to get in under the canopy."

Are you referring to sunlight that gets through the leaves? My pin oaks are in between my house and a neighbor's, both of which are rather tall. So there isn't much sun other than what would come from above the leaves as the sun treks through the sky (that is, not much comes in from the sides). Would this amount of light be enough to grow what you suggest?

Odd how different areas of the country will affect plant behavior so much :-) Ajuga here is an extremely mild mannered plant with minimal invasive properties. It DOES spread, but then that's what a groundcover is intended to do. It is also a groundcover selection I would use in only a partly or dappled shade location, otherwise it fails to bloom well and the coloring of those with dark or variegated leaves will be affected. Sweet woodruff I consider to be major pest - I find it to be far more of an aggressive spreader than the ajuga and the mat-like root system grows through anything so the plant will overwhelm many smaller perennials or shrubs in the immediate vicinity. And it is prone to a fungal blight in my area that causes dieback -- the summer humidity of the DC area may not be at all to its liking. Also not evergreen if that is an issue.

What about something like pachysandra if you are looking for just a groundcover? Evergreen, shade and drought tolerant, not too aggressive.

And FWIW, it's going to take a very vigorous and aggressive groundcover to outcompete or overwhelm an already established tree like a pin oak. Something like not maintained English ivy comes to mind :-)

The two tree trunks in this picture are two pin oaks. As you can see, aside from the trees, it's pretty open.
{{gwi:329905}}

The shade is going to be a limiting factor. However, there are a lot of shrubs that you can grow that are fine with a reasonable degree of shade. You may have noticed some things missing from my list - rhododendrons and azaleas. They don't like my winters and my soil pH, so these are enormous groups of shrubs that I just ignore.

gallicas list includes a few plants that are really sun plants ...

which means.. that her trees are limbed up.. to provide a canopy ... but allow a lot of ambient light ...

defining shade is near impossible ... what will grow in any given spot depends on whether it can derive enough energy to convert into food ... and under trees that usually begins with the canopy ...

i grow hosta ... a LOT of hosta.. i have been in hundreds of hosta gardens.. all are technically 'shade' ..

some gardens are so dark.. you need a flashlight ... and eventually even the shade plants start to fail ... e.g. under a norway the canopy is so thick that barely any light gets under it ... [though that example is complicated by the norways aggressive root structure which is only dealt with by sudden death, with a chainsaw ] ...

other 'shade' gardens ... are so bright.. you still need your sunglasses ...

the point.. is that all you can do.. is try various things ... and see what will grow under your given trees ...

back to gallica ... note they mention roses.. but SPECIES roses... which are much more tolerant.. since most only bloom once per year.. and otherwise are just a big green leafy bush.. which can generate the energy to live/thrive ... if you were to try a hybrid tee rose.. which blooms repeated over the season .. with minimal leaves[comparatively speaking] .. the plant will probably live .. but your flower production.. if any.. will suffer ...

if one could not dig holes.. and garden under trees.. then there would be no hosta gardens.. nor shade gardeners .. eh ...

if you are going to stay in this house a long time.. and you really think you will be encouraging the gardening bug.. you really ought to start by considering whether you should invest in raising the canopy of your trees.. and perhaps.. even getting rid of trees that will not cooperate ... it is much easier to have tree work done.. BEFORE you build the garden.. rather than later ... [this is the hosta lovers biggest regret, in hindsight]

if in fact you do have to remove a tree.. simply replace it with a better tree.. mother earth.. net zero ... no guilt ...

good luck

ken

I've always considered oaks ideal for shade gardens. You can grow anything under them that will grow in shade--an enormous list. And there are Ajugas and then there are Ajugas. The common green variety is indeed invasive. But the multicolored ones and the little 'Chocolate Chip' are usually restrained.