Close, but no cigar! The main reason for not planting in soil thats too wet is because the soil particles in wet soil pack together much more tightly than they do with moist soil, and that excludes the "air pockets" that are needed in the soil for the rootsplant roots need air as much as we do! ;-)
Heres how I put it in that other thread: If you work in the area and plant when its too wet, itll become badly compacted, and when it dries out youll wind up with something akin to concrete.
Thats especially true out here where most of us have some degree of clay, which, because of the nature of the clay particles, tends to naturally pack together much more tightly than the soil in, say, the Midwest where they have nice loamy black soil. So mostly youre just trying to keep from creating a bunch of clay bricksunless youre trying to build a house, that is! And as I implied above, you dont want to be walking around too much in areas where youre gonna plant when the soil is really wet either since that just tends to pack the whole area down, potentially making it harder to work in when you start digging.
The cold could be a factor, but for the most part I think that as long as the plants are well hardened off that wouldnt be as much of a problem as compacted soil would be, tho I agree with Dan that if something was planted and then just sitting in cold, wet clay soil for too long it could cause problems. If your soil is dry enough when you plant them, they should be just fine even if it stays cold out. When you plant them, water them in well, and then dont water again until the soil just BELOW the bottom of the roots "crumbles." Dig down into the soil right NEXT TO where theyre planted to do the crumble test to figure out when they need to be watered again after theyre planted (dont dig into the backfill soil). If you keep the surface of the soil on the level of the existing roots wet all the time, the roots have no incentive to grow deeper in search of water, so your watering pattern should be to gradually stretch out more and more between waterings as they start to grow. That promotes new, deep root growth, which is what will make them good, healthy plants/trees, and will make them as drought tolerant is possible.
And, yes! The "dry enough" soil rule applies to anything and everything youre going to plant. The "crumble test" is a really good way not only to determine when the soils dry enough to plant in it, but its also a great test to decide when plants need to be watered, as I explained above. It works really well when people are having watering problems and cant figure out when or how much to water.
To establish good watering timing, dig down into the soil in the area in question, either to the approximate bottom of the existing roots or 6-8" downwhichever comes first. Take some soil out of the bottom of the hole and squeeze it in your hand.
~ If it packs together and doesnt easily crumble, the soil is wet enough. Wait several days and dig againin a new spot.
~ If it packs together and then easily crumbles between your fingers, its about time to waterdeeply.
~ If it doesnt pack together at all, its way, way too dry. Water deeply, wait 24 hours and repeat.
When you do this 2 or 3 times in a particular area, youll get a pretty good feel for how often you need to water to keep the deep soil wet enough and let the top several inches of the soil dry out enough to establish healthy plants.
And to water most of our clay soils "deeply" you need to water slowly, which means either with a sprinkler with a fine spray, or watering for short (10-15 minute) periods of time and waiting an hour or two between the short periods. If the water is put down too quickly much of it will run off and not really soak inagain, because of the microscopic nature of clay soil.
If you want to find out if youve watered deeply enough, wait 24 hours after watering and then do the dig-down-and-check-your-crumble test again, always digging in a different spot since loosened soil wont accurately reflect the moisture in the "undug" soil. If it doesnt crumble any differently than it did before you watered, you didnt water deeply enough. If its adequately watered, it shouldnt crumble easily anymore.
Since youre going to be planting so much I just thought I may as well post the whole "lesson!" Let me know if something isnt clear.
It sounds like you have a lot of work ahead of you this year! Happy digging!
Skybird
Q
What to do with foot-long new growth on yews.
Q