The first thing we've learned is that there apparently is quite a difference in the quality and expected life of grow bags, because we're now going to be repotting 572 raspberries in new bags this spring--after our bags basically disintegrated over the course of the winter, less than 9 months after planting. The bags seemed to be getting weak last fall, but the plants impressively broke out of them this spring, either splitting them as the root systems grew, or sending new canes through the sides of bags - sometimes through the drainage holes, and sometimes just through the sides of the bags.
The bags being used at Michigan State where they have more experience with this system, have generally lasted for 4 years. However, I found out from talking to Eric Hanson today that he had a similar experience with one batch of bags several years back. So, if you use grow bags, be sure you get some sort of assurance from the company that they will hold up for the length of time that you need them.
In other interesting matters, we've struggled a bit with how to overwinter the raspberries given that we don't have a cooler available to us for storing them. We laid the plants down under 2 layers of row covers inside the tunnels, and this did seem to work quite well (as long as you control the voles), right up until the last couple of weeks of fluctuating temperatures. So, we stood the plants up when they started to grow at the end of February, then laid them back down during the low temperatures in the single digits last weekend, stood them up again this past week with highs in the 50's and 60's, and now are laying them back down again with outside lows forecast in the single digits again for this coming weekend. Not kidding.
Generally the low temperatures in the tunnels haven't been that much different than lows outside, so I'm making an assumption that the plants need to be under row covers when it gets this cold. If we get a summer crop, I will be completely baffled as to why, because this should be enough to kill off any normal flower buds.
The bottom line to this is that if you have raspberries in containers, being able to move them into a cooler for the winter is really best (assuming your bags stay in one piece). Then you can wait and take them out of the cooler when you are ready for them to grow. Eric H. pointed out that you can also wait until the irrigation system is operational, instead of needing to fuss with draining the lines several times.
If you don't have a cooler, the next best option is probably to overwinter the plants outside either under a white film or perhaps a nursery cover. At any rate, it would be better if they were somewhere other than in a single bay tunnel that is kept covered for the winter with clear plastic, at least for a winter like this one, since they hopefully wouldn't take off so fast in the spring. On days like today when it's both sunny and windy, we haven't been able to vent even though it certainly is toasty in the tunnels.
On the bright side of things, I do know that we always learn a lot from trying new things like this - even if we what we learn isn't what we expected. So, we'll keep you posted on what's working, and what isn't. It certainly should be an interesting year.
Growing Raspberries and Strawberries in Containers