Where can I get Wormwood, tarragon, mugwort (Artemisia), etc. plants and/or seeds to grow?
I would recommend doing a local search for your area to find any retailers or even mail-order catalogs. Your local garden center may also be able to help. You can also check out eBay. In my experience, eBay is actually a great place to find unusual plants/seeds. Just check the feedback on the seller before you buy.
For growing information, these articles should help: https://www.gardeningknowhow.com/edible/vegetables/celery/wormwood-plant-growing-sweet-annie.htm
What does artemesia do in the winter? Does it die back or stay like the summer?
Silver Mound grows in zones 4-9/
The plant will go dormant and die back in the fall and grow back in spring.
Here is a link with more information.
Can wormwood be planted near a black walnut with success? It's in the aster family, which apparently is tolerant, but I know that's no guarantee. Thanks in advance.
It appears that this plant will tolerate the juglone of the black walnut. This article will help:https://www.extension.umn.edu/garden/yard-garden/landscaping/best-plants-for-tough-sites/docs/08464-complete.pdf
i need artemisia annua seeds
Gardening Know How doesn't sell seeds, but Artemisia annua seeds can be ordered from many online retailers or obtained from local gardening stores or gardeners.
I planted a Artemisia silver mound in a pot this summer - while it is growing quite well, I have been told that it will not 'come back' next spring/summer in a pot. Can I transplant this into the ground in the fall? I am in zone 5
You can absolutely transplant your artemisia when weather cools down. If you have a garage, it might survive winter there where desiccating winter winds won't affect it. But you will have to water it (infrequently) to keep the roots from completely drying out. In the ground, leave the leaf stems intact as they will trap fallen tree leaves and help to insulate the plant. Snow is also a great insulator from those drying winds. Roots can freeze and still make it through the winter unless they are dried out. This is why watering well into fall is very important to plants.
It started the summer beautifully, but now has fallen flat and looks leggy. What should I do? I plan on mulching around the plants to prepare them for winter...
There are a few things that need to be done in order to maintain the plant. Division and pruning to maintain shape and order will be necessary. Pruning will, also, cause it to bush out. This article will offer more information on the care of the plant: