Keep them in a cool, dry, dark place and they may last that long, especially since you can plant just before the last spring frost in most areas, which for me is March. Here is a link that might be useful: Sinfonian's garden adventure

Hi Tree, I'm in zone 5, and I have dill all over; I let it volunteer. The BSTs seem to prefer parsley for me; don't know if you're considering that one too. They've also used fennel too, but I find more cats in my parsley bed. I think your plan sounds great. Don't know about the retaining wall idea because it might take a while for the Dill to reach the size needed to show up behind the wall. Plant lots of whatever you put in; once they find your plants, you'll get egged. I'm in zone 5, and the plants all seem to do well in full sun with amended soil, which you probably have since you're planting into a flower bed. Have fun! It's addicting...I started with planting for monarchs, then BSTS, now I'm going all out for some other differnt kinds of cats (Question Marks, Buckeyes, Red-Spotted Purples, Viceroys, and trying to get some nettle for Milbert's Tortoiseshell!).

Plant the seeds after the threat of frost is over, when the soil is warm, in a very sunny place. Keep them constantly watered till they grow a few inches tall. It's fun to watch the goldfinches pluck the petals to hasten the seed ripening. After that, you can just use pantyhose to cover the seedhead, but you can also leave them open and watch the birds have a good time till all the seeds are gone. People usually cover them in order to harvest the seedheads, to eat the seeds themselves. I'd rather watch the birds! Enjoy your flowers!

I agree with Carol that these potato towers sound so promising in spring, but the people who use them rarely come back and report their results, and I suspect the reason why is that they don't produce as well as potatoes in the ground. Several folks on the vegetable forum have tried them over the years, and in every case that I can remember, they were disappointed with the results and stopped trying to grow them that way. Often, people who are simply delighted with the potato production in towers, boxes, bins, etc. are not getting any more potatoes than people like us get when growing them in the ground. I can see where folks with horrid clay or very rocky soil would prefer to use methods that don't involve digging deeply in the ground though. If you want to do it, choose late-season varieties because they will give you a heavier harvest in the potato towers than early or mid-season types will. All the potato varieties I've grown tend to set all their tubers along about 8" or so of underground stolon and that's it. They do not keep setting tubers higher and higher, for example, if I keep mulching and mulching. Sometimes you can find people on the internet doing things in their climate that we cannot successfully do in our climate. Potato production is impeded by heat, and we have plenty of heat here. Potato plants grow best when nighttime temperatures are between 45-55 and daytime temperatures are between 60-75. In addition to that, they need to set and size their tubers before soil temperatures reach 85 degrees. That is the temperature at which the initiation of potatoes ceases. Your results, therefore, will depend a great deal on how quickly it gets hot. I just store my potatoes either in the back and darkest corner of the walk-in pantry or in the tornado shelter and we enjoy them for as long as they last, which usually is well into autumn as Dorothy noted. You have nothing to lose by trying this method because you'll surely get some potatoes, but in order to know if it is the best method for you, you might want to try growing some of the same variety in the ground at the same time so you can compare the performance of the two planting methods to see what works best for you.