In some cases, plants can secrete toxins into the soil around which they are growing, in order to inhibit competition. Black walnut is a famous example, but in nature, there are a great many more such examples. That said, plants can be seen growing around each other everywhere, so by no means is this a universal situation. What's more, only certain plants are susceptible to such exudations.

It is almost a certainty that you will be able to plant as you wish, with no repercussions. Some minor disruption of the oak's surface roots may ensue, but trees are adapted to handle this with ease. In any case, the fine "feeder roots" which do most of the absorptive work of trees are not permanent structures anyway, growing, dying, and recycling over the course of a single growing season. Plant away!

+oM

Typically, it is the other way around - tree roots can hamper development of shrubs and other plants. Oaks are typically easy trees to underplant and I wouldn't worry about any shrub's effect on the tree's growth. Its root system is more than well-established if it's a big tree. Just make sure the plants you select are tolerant of any shade the oak may cast and that they receive any extra water they may need to become properly established -- tree roots can be very greedy in that regard.

And I'd be very skeptical of reports of holly roots killing a tree.....just not likely to happen if both are receiving the care they need. Various hollies grow amongst other plants without issue.

The major risk is that you will physically damage the oak's roots by digging underneath it, or drown it by over-watering your new plantings.

Avoid anything that needs a lot of water and avoid planting vines.

That admonition to not over water in vicinity of an oak is primarily a west coast thing. Eastern US oaks are much more forgiving in that regard. Since I don't know where you are, it's impossible to say whether this should be a concern or not. Of course, one should never "over water" anything anywhere, given that term is by definition an indication of excess.

+oM

what ed said ... the biggest damage will be you and your shovel to the tree roots ...... but the result.. is the trees reaction to grow feeder roots where you cut its roots ... of which.. it will then use.. to compete with the plant in the hole ... [sharpen your shovel.. it really helps when slicing thru tree roots .. and simply move your hole a few inches this way or that.. if you hit anything bigger than a shovel can cut]

this is general tree lore ... though oak is one of the easier ones to deal with ... crikey.. a maple will fill the hole with its own roots in one season .. and suck the life out of everything... unless you take care ....

most of this is based on my care of my 1600 hosta ... us hosta peeps are tree experts.. on some level ...

the real trick.. is to bare root your new plant... plant in native soil which you dug out ... NEVER amend the hole.. NEVER fert only the hole.. and NEVER water only the hole ...

the idea being .... is to NOT encourage the tree to put all its new feeder roots into the hole you dug ...

in MI.. i have never heard of not being able to water under an oak ... if that were the case.. i would have to get rid of half my hosta ...

anyway.. after planting and one good soaking in ...... broadcast all water .. but do check in drought ... properly mulched.. most of the things you note.. do note need a lot of water... for very long ... see link on proper planting ...

good luck and have fun

ken

Here is a link that might be useful: link

Sounds great for a shade garden. There are lots of ferns, hostas, Rhodedendrons, Azaleas and tons (well, lots) of shade perennials and some shade annuals. Japanese Kerria shrubs have yellow flowers, I have 2 of them under 2 seperate oaks. I would rather have a shady yard than an open sunny one any day. Well, that is of course my opinion, though.