Years ago, I read somewhere (maybe in Patrick Whitefield's How to Make a Forest Garden?) that Robert Hart (food forest originator and pioneer in England) allowed the naturally occurring nettles in his garden to grow up through his gooseberries and currants. The nettles provided many functions, including their normal nutrient accumulation, caterpillar host, delicious human spring green vegetable, and host for early harmless aphid species allowing aphid predator populations to build up in preparation for arrival of pest aphids on other plants. But Hart specifically allowed them to grow amongst his Ribes species because gooseberries and currants can take a lot of shade, such that the nettle supposedly didn't interfere with their crop, and the nettles kept birds out of the berries. Once harvest time arrived, Hart would cut the nettles down and use them as rich mulch, and harvest the berries.
I planted Urtica dioica (seeds from Horizon Herbs) nettle amongst our gooseberries and currants as a precaution against bird predation, and as a way to work nettles into the yard in a useful way. So far we haven't had problems with birds eating anything in the yard, except for scrub jays going for our hazelnuts. We get some birds in the yard, eating some seeds (bushtits eating parsnips, goldfinches & nuthatches & downy woodpeckers eating mullein), some cherries, some berries; but so far no major wipe-out-the-crop harvests. We don't mind sharing some!
Unfortunately, our Ribes have not done very well in terms of crop yield. We planted them in fall of 2006, so have had three years for possible harvests. I forget whether anything notable happened in 2008, but they may still have been establishing. Last year (2009), they got hit badly by an outbreak of currant sawfly caterpillars, who feed on the leaves of currants and gooseberries and stripped some of our bushes almost totally bare of leaves. I noticed their frass (poop) early on, but thought it was dirt the chickens had kicked up onto the leaves. Not until a week later did I notice the leaves being devoured and associate the frass with the worms. I immediately started hand-picking worms to introduce them to the chickens; then started shaking the upper branches to send worms to the ground for the chickens to devour; and after a few days trained the chickens to look on the lower leaves for worms. The chickens did regular patrol of the bottoms of the shrubs from then on, and I shook down the upper branches every few days, and we got the sawfly population under control to the point where the bushes all recovered fine, but they didn't bear any fruit last year. Note: I don't attribute these sawfly woes to the nettle; I just figured I should write up this experience while I'm at it.
This year, we had a few sawflies, but not too bad. We had hundreds of gooseberry fruits developing, and all looked promising. Then, while we were out of town for a week, much of the developing fruit vanished! Maybe birds came through and ate them (though I doubt it, since they hadn't ripened yet.) Maybe the bushes just dropped their fruit in the same way many fruit trees do a "June drop" of poorly pollinated or over-abundant fruit. (I heard from someone else in town that their gooseberries did the same thing.) But possibly we had problematic competition between the nettles and the Ribes, for either sunlight (seems unlikely given the shade-tolerance of Ribes), nutrients such as nitrogen (possible, though I do pee on the nettles & Ribes a lot, and the nettles are supposed to be deep-rooted and supplying nutrients to a polyculture), or water (most likely, since we don't water much during our three month drought season.) Even without specific disease or pest problems, our Ribes wound up looking pretty ragged by now, with curled and browned and maybe some yellowed leaves. So between the poor fruit yields and the general sadness of the plants, something isn't working.
Nettles are a pain. Duh. Managing nettles growing through fairly densely branched Ribes shrubs is an awkward pain. Trying to maneuver my hands down into the bottom of a sharp-thorned gooseberry bush to cut down nettles is a pain from two fronts.
Nettles grow fast! They stayed quite manageable for the first two or three years, but this year they've gotten established enough to really take off. They've spread runners into the paths (both the small 1.5' paths between Ribes shrubs in the tree understories, and into our main 2' and 4' paths between trees). It now requires more than an annual chopping of the nettles to keep them out of our way; I have to go in every week or two in the spring to cut them out of the paths. Of course, a lot of that maintenance dovetails well with harvesting them as my favorite spring vegetable. But once they start to flower, you're supposed to stop eating them because their calcium oxalate crystals can damage your kidneys, so at that point I'm just chopping (ouch! it stung me. ouch! damn gooseberry thorn.) the nettles to keep them out of the paths and try to open up some sunlight for the Ribes. And this kind of work, though it occurs in shorts & t-shirt warm weather, really demands pants and long sleeves to minimize masochism--which means I have to dress up special for the job. I haven't dressed up real special since I got old enough for my mom to stop dragging me to church; and I haven't dressed up semi special since I quit my corporate business casual job, and I don't often get around to dressing up special for the nettles either. So the paths get more and more overtaken and the Ribes seem to suffer and we got hardly any berries this year.
When we do get around to chopping back the nettle, we're now ripping out as much of the root as we can get, to slow it down a lot more than just cutting the aboveground growth would. I don't think we'll try to totally eradicate it, but we'll do more to set it back. In my next yard design, I'll definitely still include nettle, but as its own patch where I can just chop it back with a machete from the edges to keep it in check, rather than having to maneuver through and around other vegetation or branches to get at the nettles. I might try planting a shade tolerant low-growing evergreen (violets?) to provide a solid ground cover through the full yard. And for Ribes, I'll try a less robust and non-painful vine--perhaps annual garden peas or annual or perennial beans or Apios sp (groundnut) or Lathyrus tuberosus (earth chestnut - I did plant this originally in 2007 with the Ribes, but they've never taken off--maybe from chicken abuse, or maybe not enough water. Two plants were still alive early this spring, but growing slowly and definitely getting shaded out by the nettles. I wasn't able to find the plants a month ago.)
In conclusion, in the future, unless we have active bird predation problems, I would not plant a combination of nettles and berry shrubs again. Especially not nettles & thorny shrubs!