Help me find out what's wrong here

This spring my neighbor put in a new fence between our properties at the back. In doing so, he dug out a lot of subsoil and a lot of it got chucked on top of my beds in the process. When he had finished the fence, I planted up the beds with some annuals and kept an eye on the perennials, but things have gone from bad to worse, as seeds have not come up, or are dying, seedlings have disappeared, and perennials suddenly started wilting and losing leaves at an alarming rate. I've attached two photos, taken on the same day, of feverfew from the affected area and an unaffected area for comparison.

We have a very small property, and the new fence covers maybe 10 m, and seems to be affecting areas up to about 1.5 m to 2 m away from it. The smaller, herbaceous plants seem much harder hit than the trees and woody shrubs--two apples, a rose, and an ornamental currant appear to be unscathed. The feverfew, runner beans, calendula, comfrey, garlic, nasturtiums, oregano (some of these planted after the new fence, and some already present) look dreadful. In fact, even some of the weeds can't seem to handle it--I've lost some dandelions and the chickweed entirely, though this could be due to its short growing cycle, I admit.

Could it just be the presence of the subsoil that's affecting these plants? Some of the plants affected haven't even been in direct contact with the subsoil, though maybe some rain has washed it nearer them; I would also estimate the subsoil is no deeper than about 6-8 cm, and that is only right up next to the fence. The only other thing is that he's not organic, but the fence between us (now and before) has always been 2 m tall and without gaps, so any herbicide could have only come onto the beds from that subsoil.

What kind of fence?

Am I right in thinking that the white boards in back of the sorry feverfew is the new fence? Was it treated lumber? Maybe 1.5 to 2 meters is how far substances in the fence boards can travel before they are degraded by soil biota.

I'll wait for you to confirm my guess before I hazard a recommendation on remedial action.

Was the fence sprayed in any way ?

David

What was the area before? Are you in an urban or rural setting? There could be something toxic persistent in the soil that got chucked. Is the neighbor someone who is likely to spray roundup type stuff?

I was thinking more like creosote

DAvid

What kind of fence?

Yes, that's the fence behind. It's got what I think are pre-molded concrete panels as a base, and what looks like treated lumber above, though the wood is not touching the earth at all, just the molded base. I don't know exactly what was used as a foundation for these panels, though he had a cement mixer, so I assumed it was just concrete.

Was the fence sprayed in any way ?

I haven't seen my neighbors spray anything on the fence, although I didn't really supervise the construction of it; my husband had already given them permission to be on our garden, so I made myself scarce to keep my blood pressure in check--I couldn't bear to see them trampling over my precious bed!

Matu Collins wrote:What was the area before? Are you in an urban or rural setting? There could be something toxic persistent in the soil that got chucked. Is the neighbor someone who is likely to spray roundup type stuff?

Last year I grew runner beans, nasturtiums, garlic, kale, tomatoes, and more in that bed. This bed was very productive last year, and I also threw on a load of chicken bedding during the winter to make the worms happy, so I was gearing up for another good growing season.

We live in a village, and this neighborhood has been urban/suburban since at least the 1930s.

I honestly don't know if my neighbor uses roundup, but I don't know if his use would be able to contaminate my plants. Unless it persists in subsoil? I don't know.

he had a cement mixer, so I assumed it was just concrete.

Bingo! The lime in the concrete mixture has leached into the soil and shot up the pH to where the plants don't like it. Two solutions: (1-lazy) wait for the rain to leach it out or (2-involving work) dig a trench along the new concrete and backfill it with peat. Or if there is a cheesemaker nearby and you can get some whey, the acidity of the whey will work to neutralize the excess lime, pour that into the trench.

My money would be he treated the wood on the fence with a spray . Ronseal or similar. If you look at the wood does it look like it has been sprayed?

David

My first instinct is that it has to do with the concrete too. It could be the pH or something else like a change in the micro-climate. Concrete can suck up water pretty fast and evaporate it away from the soil like a wick. The mass of the concrete could also be messing with the temperature in that area or reflecting more light onto or away from the plants. Is it possible to check the temperature through the day to see if it's somehow cooking the plants? I have one place in front of my house where a window reflects and focuses the sunlight enough to melt plastic at a distance of ten feet. Fortunately that happens in winter when things aren't likely to catch fire. It took the loss of three tarps over three winters for me to figure out what was going on.

Thanks for the suggestions! I think John is right, it must be related to the concrete. We've decided to let it wash through and hope we can use it next year. My husband threw another load of chicken manure on top and I'll be moving any plants which can still be salvaged.

We had a chat with the neighbor, and he said it hasn't affected his garden, though the section which has the worst effect on our side has a patio on his side.

I just wanted to update and say that though the bed is still pretty devoid of life, it's starting to recover a little. Normally this bed is drowning in self seeded nasturtiums this time of year, which I generally chop and drop in order to keep them from smothering the rest of the plants--those seedlings all died in late spring/early summer, before they had a chance to grow much. Now there's a few new ones popping up here and there. I've put up a couple small raised beds on top of the soil, put down a thick barrier of newspaper, then compost, and a little of the affected soil from the bed itself. The plants inside (winter greens and peas) are doing well, considering! And have very little slug damage, unlike the rest of the garden.

Luckily the larger shrubs and trees have been largely unaffected, and the smaller rosemary and hyssop have been growing well, though they may be partially sheltered from the pH change by the cherry tree between them and the fence. One rose bush right next to the fence lost all its leaves and buds, but has regrown a few leaves now. I was able to save a couple of the worst affected herbaceous plants, and did not lose anything larger than the feverfew--which I have plenty of, as it self seeds prolifically!

Has your soil and plants recovered? Did you conclude it was the alkalinity from concrete? Curious minds want to know!

I didn't have a soil test--I never even thought to pour vinegar on it like you did, but I'm pretty sure it was the pH change from the concrete, yes.  Six years on, it's the least best part of my garden, but still ok.  The rosemary and hyssop above ended up dying after all (but I have bad luck with rosemary so it might not have been related).  The cherry tree is still alive and producing;  it didn't seem affected at all.  I think I just planted it up as normal the following year and every year since;  this year I have some runner beans, kale and tomatoes in this bed, plus some self seeded chard.  Right next to the fence there is still a patch of bare soil where not much wants to grow, though it looks like some grass trying to colonize it this year;  this is only within about 15 cm of the fence.  Things are growing beyond this.