Without pictures it’s hard to say because we can’t see just how many trees there are. Under trees there is an issue with shade as well as roots. If you think there is sufficient light the roots are less of an issue. Your best chance of success is to choose shrubs suitable for shadier conditions and to plant small specimens. They'll be easier to plant and water and will establish quicker than big plants. The tree and shrub roots will sort themselves out so you don’t need to ’keep the pre-existing root system at bay’. I’m sure you're perfectly capable of doing the work and I wouldn't waste my money paying someone to do it. It’s just a question of digging a hole and planting. The holes dont need any ’preparation’. Just dig and then back fill with the soil you took out. Water the shrub in copiously and mulch over the surface around it.

The majority of tree roots are located between 6 to 12 inches below the soil surface. There are larger roots closer to the trunks, and some trees send large roots way beyond the tree's canopy. Shrubs are actually the better choice for planting around mature trees. The main problem with planting below trees is that roots suck up moisture and the soil dries too quickly for many plants. When digging a hole for a shrub make the hole the same depth as the potted plant, but twice as wide so the roots can grow easily into the native soil. Refill the planting hole with the native soil, then water well. Depending on your climate you may need to wait until September to plant to avoid heat, or even wait until next spring if your winters are very cold.

The amount of light that gets to the where you want a shrub also determines which shrub you should use. Part shade receives roughly 2 to 4 hours of direct sun each day. Dappled shade is sun that filters through openings in a tree canopy during the day and can provide as much sun as part shade. Medium shade doesn't allow much sun through, but it's still bright. It's usually found under trees with very high branches. All of these situations will easily support many shrubs. Full shade is found beneath mature trees with dense foliage, usually large leaves, and a spreading canopy. There are few shrubs that do well here.

Should your trees provide too much shade the situation can be remedied by removing the lowest limbs. This can easily be done by a home owner. It usually allows more light to get in during morning or afternoon, though it may reduce the canopy enough to produce medium or dappled shade.

Five-leaf Aralia (Acanthopanax sieboldianus) grows in full shade to full sun in zones 4-8, but can eventually grow to 10' tall and wide. Sweet Pepperbush (Clethra alnifolia) grows in medium shade to full sun in zone 3-9, and gets up to 8' tall by 4-6' wide. It prefers acid soil, but will tolerate other soils as long as they do not dry out. Ninebark (Physocarpus opulifolius) prefers part shade in zones 2-9, but will tolerate more shade in warmer climates. It gets 5-8' tall and 4-6' wide and tolerates dry soil. Do a search for "shrubs for dry shade" to find more. Or, visit a local nursery for advice.

Thanks Floral_UK...yeah, I imagine that makes sense...that the pre-existing roots in the yard, and the roots of any new shrubs I plant will all 'work themselves out'... ;-)

One thing to ask is what type of trees these are. Maples for instance create dry conditions and tree roots stretch out many yards further than the trees . I finally came to understand why many plants I planted failed to thrive.

Does letting the yard go wild and natural mean the grass won't get mowed at all? If it does, you might want to reconsider that, as untended yards eventually just become weeds and tree seedlings and look unkempt. It takes a lot of effort to have a nice looking ”natural” yard. I have had luck growing ground covers in heavily tree rooted areas by using lily of the valley and pachysandra. I am also in New England and have had mixed results with cold hardy azaleas (Exbury) but the ones that make it look spectacular so they are worth trying. Garden centers try to push rhododendrons but they loose too many leaves to winterkill in my experience.

I have a lot of Maple Trees, Spruce, a sycamore, White pine, all surrounding my small property in the yards of my neighbors. I have two mature Maples and a Japanese Maple in my yard. I have planted shrubs and it's really been difficult to get much to grow, except in areas that are a distance from tree roots. Anything I planted under the tree, did not thrive and eventually was dug out. Even shrubs that are said to be able to tolerate those conditions. I have some at the dripline that do okay. Taxus right near a mature Maple have no problem. I have one western Arborvitae which is growing within 5ft of a mature silver Maple that has done great, tripled in size already. But, it needs a lot of attention to watering. If I let it dry out, I get some browning and I hate that, so I have a soaker hose under it and especially in dry spells I make sure it gets enough water. I had Viburnums that grew in those conditions but, they ended up with pests and other reasons that made me eventually pull them. I just had no luck with them. Oakleaf Hydrangea has done very well, right under the dripline of a large mature Maple. Clethra as well.

In my darkest corner, between two Maples, I tried so many things that didn't work, then I planted a Gray Dogwood [cornus racemosa]. It took off. Grew to about 8ft pretty quickly. It spreads and if you can't keep up with it, it might be a problem. I'm surprised with all the shade, dry conditions and roots that it didn't slow it down. I haven't found it that hard to keep up with. It's better to check it every spring and remove a couple of small ones. If you want you can wait for every 2 years and check and end up taking out about a half dozen a little larger suckers. I'd rather it didn't sucker so much but, I put two Hydrangea endless summer in front of them between them and the lawn and for whatever reason, they have not spread into the lawn at all. They are pretty easy to remove the suckers. A shovel and some yanking and I get them out with the root easily. I have thinned them and pruned them after storm damage and they come right back strong. They don't get more than a couple of hours of morning sun yet they do flower - white flowers. They have a lot on them this year No pests or disease in the 8 years I've had them. The flowers turn into white small berries that the birds strip. It's supposed to get red fall foliage which I would love, but mine doesn't for some reason it has yellow fall foliage.

I agree with what others have said, buy small shrubs and you'll be surprised if they are happy, they will grow fast.