You can plant fava beans as soon as you can push a finger into the soil, say in early April. But they would be better as a food crop, because the fixing of surplus nitrogen doesn't happen until the plant is mature. By the way, old timers in southern Michigan used to plant them in September to over-winter. Bu I have found they need a bit of protection. Regards, Peter.

the issue is winter heave ... unlike trees/conifers/shrubs ... perennials need to get into the ground.. so they can GRAB HOLD .... before ground freeze ... its really a matter of day temps versus night.. for odds of success ... do not transplant if 100 degree days and 75 degrees nights.. just too much stress... but if night temps are getting into the 50 or 60's .. then then can recover from whatever the day temps are ... its all about getting some roots to grow .. to hold on.. a good blanket of mulch really helps .... I NEVER FERTILIZE IN MY Z5 AFTER ABOUT 8/15 ... we do NOT want lush vegetative ... GREEN .. growth late in fall.. we want the plant to harden off properly .. so dont get some bright idea that you can HELP your transplants with a heavy dose of fertilizer ... ken

If the plants are fully hardy for your zone, there is no real need to be overly concerned about last frost date. Too late or too early still runs the risk of frozen soils, but if the soil is workable and the plant hardy, you can plant. Frost dates are generally used as benchmarks more with regards to tender perennials/annuals. Perennials with more succulent foliage, like hosta, can be damaged (not killed) by cold if they are fully leafed out then but will releaf rapidly. Although my soils don't freeze to any significance here, we do experience lots of frost, some rather late season and some quite severe. It doesn't bother the perennials at all. I've even planted a full perennial border in mid-December right before a 2 week cold snap into the low 20's - the plants never even blinked.

I always plant my leeks about now, and start harvesting them in the fall when they get large. When it starts getting cold I give them a deep fluffy mulch and continue to harvest until the garden is too deeply buried in snow to harvest. Once the bed re-emerges in the spring, I have just a very few weeks to harvest and eat the rest before they start bolting and get tough. The top gets frozen and looks relatively unappealing, but the part that is deeper in the mulch looks fine. I am not a market gardener, but I think that having them in a tunnel to keep them from getting too cold will keep them looking more handsome for sales, and in really cold weather you may want to use spun bond row cover as well. IME leeks will continue to get larger, but not tougher, the longer the growing season, but will just stay the same size once the temperatures cool and the light levels decrease. I am not sure what the advantage of starting them later or the disadvantage of starting them earlier would be, but that may be because I have a relatively short growing season, usually about 4 or 4 1/2 months.