Barb, that's a good one - Off!
:-)
My most recent gardening mistake happened last week. I was moving some canna lilies and accidently cut the sprinkler pipe that is buried in that bed. It wasn't pvc, it was funny pipe (much thinner). I didn't realize I'd cut the pipe with the shovel for several days. It's in the back of the bed near the fence, so I just didn't see it. By the time I did notice it, the sprinkler water rushing through the pipe had dug out a trench over 1 ft deep and 3 ft. long exposing roots on amaryllis, canna lillies, crinums, etc. Ooooops! I don't know which was more unhappy...the plants or my husband. But he was a good sport about it...even though he had to repair everything after work...in the dark. I helped. I held the flashlight.
Kathy

I'm surprised the pipe wasn't pvc and thin to boot.

I know DH's hate it when there's repairs to be fixed but it happens.

I don't have a sprinkler system wish I did. I have soaker hoses set through out the beds. The lawn I water by hand or set up the old sprinkler but mostly sit outside and hand water. I enjoy sitting out there in the early mornings when I can.

My worst mistakes usually involve planting something that has turned out to be invasive, and not being able to get rid of it later.

The worst one has been dividing the anenomes that grew here when we moved in. I still love the flower, but I wouldn't have transplanted it all over the garden had I known the problems it would cause.

Ribbon grass was another one I planted, but I've since done a pretty good (back-breaking) job of digging it all up.

Hmm, I'm not sure which mistake was worst. Several have been a nuisance, that's for sure. Probably the biggest one was planting 'Kwanso' daylilies from a friend all along my car port. It's not that they were too invasive, it's that there's too much shade there, and only the front clump blooms. The rest of that (long) space was just scraggly foliage. So, I just dug all of that up this week (except for the one clump that blooms).

Another was planting daylilies along my back fence after we bought the house, before I realized that it is too hot and dry there for them (bushes with greedy roots from my neighbor's yard make that a TOUGH place for many plants). And, I didn't do it once, but TWICE. Once with 'Arkansas Post' daylilies from Burpee, and once a couple years later with a mixed bunch of yellow daylilies from White Flower Farm. Now I have NO 'Arkansas Post' at all, they all croaked, and only three of the original 24 mixed yellows (only one of which was yellow, and I gave that to my sister - of the others, one looks like 'Siloam Ury Winford,' and one looks like 'Autumn Red'). Now golden barberries, golden euonymus, irises and nasturtiums seem happier in that location.

Oh, well, live and learn. (Or, live and learn SLOWLY in my case! LOL)

Laurel

Lets see, planting Dl's in 100 degree weather was one mistake, planting evening primrose and chamelion plants in my garden was another mistake, oh and creeping jenny, those three things just about choke everything around them out! And my biggest mistake was probably not buying a big enough yard to support my growing DL addiction! LOL! -Jessica

My biggest mistake ever, I think, was as a beginning gardener with a very large oak tree that nothing would grow under except azaleas. I planted ivy as a ground cover. Let's see that was some 20 or so years ago. Boy oh boy, have I got a patch of ivy now!!! It's ok that it grows under the azaleas and oaks as a ground cover, but the dang stuff just won't stay put!!! If you no what I mean, I'm constantly having to battle it to keep it under control and out of some planting areas that are close by. Never, never plant ivy as any where in your garden!!!! :)
Jan

Don't plant vinca either!

Or Mexican Petunia (Ruellia brittoniana)!

I have so many to choose from...let's see:

Could it be the four rhododendrons I planted in an approximately five foot space? (gone now)

Or the dozen azaleas I planted in the same five foot space with the rhodos? (gone now)

How about the glaring magenta azaleas I planted in front of my (then) red shutters? Gives you the shakes to think about it, I know....shutters are now blue.

Oh, and the stinky Redspire Pear I planted according to the label which I am now going to have to pay someone big bucks to take out as it is too close to the house....

Let's not forget the supposed-to-be-pink azalea that turned out to be bright orange that is planted near a pink dogwood...an eye-popping show in spring...

I could go on...and on...

I have to say, Planting a flowerbed in front of my House.
Found out the hard way " It's just to hot !! plus dragging the waterhose to the front to water. But I have since made it smaller.

I have done some of the same, planted tall purple ruellia and vinca, the vinca died this year YEAH, LOL and they say you can't kill that stuff........I can and did don't know how but so far it's gone and I hope for good. Now watch it come back grrrrrrrr.

I've planted things to close together, to far apart and have to find something to fill in the blank spot.
I was outside this morning and was trying to trim off the bad leaves on my clematis will it was tangled up like your necklace chain and when trying to get it untangled the limb would break grrrrrrrrrrr. I managed to save some of the long limbs and hope it will fill back in next spring. It was a knock out last spring.

I moved one clematis in the front yard I know they don't like to be moved but this one wasn't doing a thing in four years so I moved it.

Hmmm I've made a lot of mistakes in gardening over the years. I think this one may be the ultimate. I reviewed and redid my will recently and left this property to my oldest son. Several days later while working in the yard, he came by and asked me what I thought I was doing planting all this junk. He was just going to get rid of it when I'm gone. I may have to redo that will. (lol)

Not removing the Tree of Heaven while it was little. Now I'm continually removing the small shoots it sends up through out my daylily garden.

Letting that one Canada thistle go to seed....