For regular turnips it may be a little late, but Hakurei turnips would work very well. All those crops you listed are frost-tolerant, so you have way more than 60 days. The spinach and kale are particularly tolerant and will be fine right until the first permanent snowfall. OTOH, you have to add a 25-50% extension to the DTM to account for fall's shorter and ever-shortening days. I would also suggest radishes, tatsoi, bok choy, gai lan and claytonia. IME, freeze damage thresholds are about like this (this is without row covers): Least tolerant: lettuce and bok choy - mid to high 20s F Tolerant: beets, turnips, radishes - mid 20s F. Mound up soil around the growing root to prevent the root from freezing. Very tolerant: kale, spinach, tatsoi, claytonia - mid teens F This post was edited by Slimy_Okra on Fri, Aug 15, 14 at 21:48

I'm going through old posts looking for something else and have seen several people ask this question so will chime in with my experience. I was told that you won't get what you expect and boy was that advice correct. At the time my garden was probably 2 miles from the nearest other garden, so cross pollination from other gardens was doubtful. From the seed off white ebeneezer onions I had all colors of the rainbow in the seedlings. None of which ever amounted to anything. I played around with them about 5 years before I finally let them go. It was a fun experiement but a waste of my gardening space. Maybe others have had a better experience but I think it all depends on the heritage of the onion you planted originally.

Radishes if you like them, and as you mentioned lettice/spinach.

As Dave said, the self pollinating and self fertile nature of some plants makes them far less prone to crossing. All perfect flowers are self fertile since they have both male and female parts in the same flower. This increases the likelihood that when it is pollinated, the pollen is transferred only between the same plant, considerably limiting crossing. Not all self fertile flowers are self pollinating though. For example, tomatoes (I'm going to have to disagree with Dave on this) are not a "true" self pollinator.They generally do require outside influence to release the pollen from the anther and deposit it at the stigma. The vibration caused by the buzzing of bumblebees while feeding (there's a name for this that I can't think of right now) is perfect for this type of pollination. So, a bee carrying pollen from a Cherokee purple it just buzzed at could carry some of that pollen to the mortgage lifter planted next to it and cross the two (this is compounded by the fact that literally every tomato cultivar is the same species, Solanum lycopersicum). Of course that is a purely scientific answer and the actual likelihood of this happening in the real world has far more variables involved. I would worry even less about beans as most garden grown snap beans and peas are truly self pollinating. in They will produce a viable seed without outside action due the fact their anthers and stigmas actually touch within the flower (so that when the pollen is shed direct from one to the other). That's not to say that crossing is impossible (otherwise there would be no hybrid beans for sale) just the likelihood of it happening is even less then in a tomato. I'm also going to have disagree with Dave as to the interspecific hybridization among squash. While there is no crossing at the family level (a watermelon can not pollinate a cucumber) and in general no ability cross within the different genre of the Cucurbitaceae family, a few different studies have shown that there is some degree of intergeneric compatibility between some species of domestic Cucurbita. The most prevalent I believe being between C. moschata, C. Pepo, and C. argyrosperma (C. pepo will very easially cross with C. texana and C. fraterna, but both of them are wild types and not generally found in the home garden). C. moschato is actually believed to be a bridge between wild and domestic squashes based on is high level of compatibility with other species. This should not however alarm you. I don't think the compatibility is so great that much more then a small percent of the time will it actually result in a viable crossed seed. In reality, interspecific, and to a slightly lesser extent, intergeneric breeding does happen, both in the wild and in domestic settings. The question is, will differences in phenotype resulting from a cross be apparent to the naked eye? In some cases yes. The alleles will show incomplete dominance and a cross would be apparent at the F1 generation. In other instances though alleles will show complete dominance and the resulting F1 will be identical to the more dominate of the two parents. Such was the case in Gregor Mendel's classic pea experiment. Crossing a purple and white pea flower, all of the resulting F1 pea flowers were purple and white pea flowers did not show back up until the F2 generation. So what does this mean for the home gardener? In some instances we may save seed from an inadvertent cross and the following season we would see the effect of the cross. In others however, the "visual" effects of the cross may not show up until later generations after we saved seed again (I would suspect this to be a much more prevalent problem with crosses in the same species rather then merely the same genus). Say we again pollinate our unsuspected F1 (which looks to us to be identical to a pure butternut squash) with an actual genetically pure butternut. The completely dominate alleles could potentially repress the recessive ones again and we may never know that we in fact are breeding an impure cultivar, at least the genotypic level. The next question is does it matter? If it looks like a butternut, acts like a butternut, and tastes like a butternut, how much should we worry about the genome of our garden plants? So I told you that story to tell you this one: First of all, this is a scientific answer and the reality is that studies done in a lab and growing vegetables in your garden are two totally separate entities. Secondly, I wouldn't be too worried. Most of our garden crops will remain true to type without much help from us. The vast majority of the time, you will be fine. There are a few cases where cross pollination is a real risk (corn and same-species squash right of my head) for the most part your going to be saving true seed. If by chance you have 3 out of 100 seeds that do not grow true, I don't think that is enough to worry about, even when sharing seeds. It may also be important to note that many of these accidental crosses have actually ended up with desirable outcomes. But, If you are still worried about saving 100% genetically pure cultivars of OP crops the preventative measures are not usually difficult, and many plants do not require much, if any. This post was edited by ZachS on Fri, Jan 24, 14 at 17:56