June soil temperatures in my Vermont zone 4b trials show the moderating effect of straw mulch, soil under such mulch being 10 degrees (F) or more warmer many nights, and 10-20 degrees cooler many days, than bare soil. The average for the month under 6in. of straw mulch was 62F, the average for bare soil 71F.
While the mulch keep down the fluctuations, it also kept the soil cooler, perhaps not best for warm season crops? The range under mulch was 53-70F, the range in bare soil 44-112F. The standard deviation under mulch was 5 degrees, that in bare soil 12 degrees.
So the result from these cool temperatures (our local corn is only 6in. high this 4th of July), is little growth yet on the Panicum, 4-6in. on some at most. Bluestems are a little better, with generally poor regrowth though after winter. On the 1-5 scale with 5 best:
Carousel 3.0 (one plant dead)
Jazz (no plants received 2012)
Prairie Blues 1.8
The Blues 2.5
Also helping keep plant growth down was our excessive rain (and consequent little sun) in June, the second most on record, with over 9 in., some days with 1.5in. or so. Soil for the trials is a heavy loam. (Post written by L. Perry)