Weedwhacker said:but, but.... what if the full moon brings a late freeze

Okay, I'm just over-dramatizing... but actually I think the ideas of the full moon as an indicator of the last freeze, and "planting by the moon phase" are being somehow intermingled here. I thought the question was about the full moon/last freeze.

I can do both, try to see if the moonlight effects growth rate, and if the moons final spring full moon REALLY signifies the final frost for the season.

There are different microclimates in every zone, so even your next-door neighbor can have plants killed by frost when yours are not. eg. If you are in a low spot it gets colder at night because the cold air pools down there. If you plant on the south side of your house, your plants may survive a freeze that would kill them if they were on the north side.

Sun intensity can make a difference too - it warms the soil more if the air is clear and there are no shadows in the middle of the day. If a warm day is cloudy, the soil isn't warmed as much. Zone 9 in California is a lot different than Zone 9 in Florida because of wind, exposure, altitude, air pollution, soil density and a lot of other differences.

Apart from all that, throwing an old sheet, a cardboard box or some frost cloth over young plants for an overnight chill can save their lives, too. I do that a lot in winter, as we do get the occasional frost even here. Above all, don't use plastic though, unless you can effectively "tent" it so it won't touch the plants.

Hmm, what are the reprocussions of plastic?

It has no insulating value, so if the plastic sits against the foliage of your plant the cold is transmitted to the leaves and the leaves will freeze. If you can tent it up and make a mini-greenhouse, the air layer will insulate, and the plastic will hold the heat from the warm ground around the plant. The other danger with plastic is if you don't snatch it off before the sun hits it in the morning, the plants will cook.

That makes sense thanks