Both answers are probably right, It is like guessing when to remove winter protection. You can assume that waiting 2-3 weeks after your avge last date of frost is ok. But, if while waiting, you notice that the weather is unusually warm, well, you can chance it. If it turns out it was too early, cover them when the temps dip and make a note in a wall calendar for future years,

The "last frost date" warnings are really only appropriate with frost-sensitive plants, like annuals and tender perennials. Otherwise the only limiting factor for planting hardy perennials, trees or shrubs is that the ground is workable - not frozen or overly wet.

If the plants are greenhouse-grown and have broken dormancy and started leafing out, you may want to gradually acclimate them to outdoors before planting in the ground. But otherwise, there is no reason to wait for frost dates. They have no bearing on hardy plants.

I see yur point. Hardy hydrangeas should be able to survoive late frosts but survival was not what I was thinking of. I had the leaves and the plant look in mind with that suggestion. I usually hate to have the leaves damaged in cases where the temps dip and stay there for a while. It probably happens more in Z5a than in mine though. A co-worker in Colorado was just telling me how he had brought out some Meyer's Lemons Tree and had to move them back inside due to yesterday's snow shower and cold temps.

I cover the newly planted/potted ones if there is a "short" frost because here, the temps will probably dip momentarily and then go back up. But in Z5, I would prefer not to have to hassle with temps staying down for a while longer, damaging some leaves and temporarily affecting the look of the shrub, etc. ...

I actually had a late frost within the scope of those extra two weeks this year. Do you get many of these late dips over there tulips01? I had looked at the 10-day weather forecast and decided to get some tender potted plants out and, two days before the frost, the weather forecastsers tweaked it to include the chance of a frost. I covered the plants because it was just going to be bad for a few hours. There was still some damage but it probably will not be visible in a month or so.

Luis