Chilling the wort by my flower garden?

Brewing has been going good; made 12 batches and 10 were drinkable. Last month I had two batches in a row turn into vinegar in the primary fermenter. The reason why I bolded that is because I brought this up before and 70% of the respondents suggested the problems occurred at bottling.

Anyways, both of the batches were in a brand new bucket and I did my usual meticulous Starsan everything routine. I explained my situation to a 'pro' at my hbs, and he and I reached the conclusion that my woes had to do with my chilling the wort (with a wort chiller) with no lid by a large flower garden. The garden is right outside my garage where I do my brewing. There are all sorts of insects flying around dropping who knows what into the wort. My contamination issue did not pop up until I started brewing in that spot. I brewed 3 batches in that spot--2 turned to vinegar and the 3rd turned out fine. It just so happens that on the third batch I ran out of time for the wort chiller, so I put the lid on the boil kettle and let it sit in my basement overnight before pitching the yeast.

Anyone else have any experience with a situation like this? I'm brewing tomorrow and I'm going to put a lid on while I chill the wort....

mmmm malt vinegar! send some to me, i have some fish in the freezer

It's possible that pollen, fuzz, bee poop, etc. could be bringing nasties in. It's especially telling that you've brewed since those batches without an issue. That would mean that you don't have chronically infected equipment somewhere along the line. I tend to put a lid on my kettle as I chill for that reason, but I thought I was just being overcautious. Maybe it's a good idea. you could use cheesecloth, etc. as well.

EDIT: I also make a point of spraying down the kettle lid and the ends of the immersion chiller lines with StarSan. Lots of condensation forms on these during chilling, dripping into the wort, and they don't get sanitized by the heat.

One fruit fly lighting upon your wort and flying off will transfer enough acetobacter bacteria that it could ruin your batch. Fruit flies love wort and you might not even see one get in there while you're cooling since they're teeny tiny.