Frank, the answer is yes with the qualification that such effect may be tiny and unmeasurable. But real nonetheless.

+oM

without any specificity to any given plant..

i dont know how to answer this ...

and are you hoping to lower it a zone.. or raise it a zone ...

frankly.. i dont see what difference it makes in z8 ...

the lake is obviously going to retain heat in fall .. and retard spring until the water warms ... keeping in mind that cold air goes downhill ... so if you are above it.. it might all be moot ...

you are really on the fringe of esoteric discussions about the creation of the universe.. and how some lake affects it ... and dont get me wrong.. all the power to ya on talking about it ... but of what use will it all be in application in your garden ????

and i just wonder why this is important ... especially in regard to conifers ... and z8????

can you give us some more facts as to where you are going with this???? or what you want to accomplish???

ken

Here is a link that might be useful: link

I think this term microclimate means a lot of different things to different people, and it depends where on the globe you are vis-a-vis the amount of the effect you will see. Scads of british gardening books mention shrubs surviving on south walls versus the open garden. In a climate with so little winter sunlight energy, that could make a difference; as far south as the Gulf Coast it might make less of a difference. It was noted that some tender palms in San Antonio survived the freeze of 2011, so urban areas even raise the temperature down there during cold outbreaks. (But that's a really exceptional one because of the amount of water and sheltering large buildings) In the Bay Area (CA) being on one side of the ranges means summer highs around 70F, while they are 90F a 5 minute drive on the other side.

2 miles of lake water will, in my opinion, have an effect but not very pronounced in the grand scheme of things. What's more likely is that you will have later freezes than areas away from the lake. Of course, your freezes are pretty late down there regardless, but if open lands away from the lake have a freeze on Dec 15 with the passage of a front, you might not see a freeze until the next passage of another front 2 weeks later. However: during a big, bad winter freeze like 1985, let's say temps. drop 6 degrees below your zone temperature. Your temp might only drop 4 degree below that, but it's still going to be potentially disastrous, depending on what you are growing. Of course that would also depend on whether the freeze came in mid December when the lake is still relatively warm or in mid February when it could be close to freezing if there had been a cold spell. IIRC, the Mississippi has partly frozen all the way down to Baton Rouge during the worst winters. Just as the Atlantic froze down to Virginia Beach in the late 19th century...practically inconceivable these days.

In a place like Lake Maggiore in Italy, a lake does hugely influence the microclimate but there are a host of much different factors there. The water is incredibly deep and stays almost the same temperature throughout the year. The lake itself is surrounded by a south facing ring of mountains > 3000 ft. high, with are further backed by the Alps which form a perfectly shield shaped dome to divert air plunging down from the North pole. Hence the gardens right on the shore have proteas, Phoenix, citrus and other zn 9 plants whereas the rest of the northern Italian plains are zn 8 or perhaps 7b in the very coldest areas. (and yes, FWIW, that area had one of its worst winters in decades last year, but the plants are mostly recovering) Furthermore, almost all the trees around the lake except at very high elevation are chestnuts and other hardwoods, so the ground is mostly open to light in winter unlike a hypothetical similar place in say, the PNW.

Dave, that's what I thought but just wanted to confirm my thoughts. Two miles isn't that far for a lake I guess, and it's a shallow lake at that. I just figured someone would have experience- I've never lived this close to a lake. Later frosts would be fine by me, ours us officially 11-15 but lately it has been a lot later. The only conifer I have that comes close to being tender is Nageia nagi and that should be ok I think. I do have some Widdringtonia seedlings but they aren't ready to be planted. And one P. cariensis seedling which might not make it when it gets big enough. Live in a pine forest and have a pine seedling- go figure. They look pretty neat though.

i surely know nothing about those plants ...

but there is a water body 1500 feet down the road from me ... and the middle of my 5 acres.. and down the driveway.. is the 8 foot valley that goes to the lake ..

i was mystified by how cold air flows.. down 8 feet.. down the drive.. and down the road ... to the point that the hosta bed.. at the bottom.. becomes active ... about 2 weeks later in spring ... and goes down 2 weeks early in fall ..

and all i can figure.. is cold air.. pooling in the low spots ... and its effects on plants in fall.. and soil in spring ...

so where your garden sits.. in relation to how air moves.. should be included in you hypothesis ... but when it all boils down.. only experience.. in your specific garden.. will tell you how it all works. ..

ken

...and if you plant large trees they can form a cold air dam. At one of our research orchards we had a windbreak composed of large blue spruces. The crew had to cut holes in the break because the orchard immediately above the windbreak had a severe frost problem...