We had hosted in Missouri and love them! Now we live in Great Falls Montana and aren’t sure if they will do well here.
Yes! Hostas do well as far north as USDA zone 3. Montana has zones 3 to 6a across the state. You are in zone 4a.
https://www.gardeningknowhow.com/planting-zones/montana-planting-zones.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-3/zone-3-hosta-plants.htm
100 old Maple trees with Bark around base
Since your trees are so old, I would not disturb their roots. Trees have a lot of surface roots and planting beneath the tree canopy can cause a decline in the tree's health. The best thing to put under trees is a layer of mulch out to the dripline.
I would like some plant/flower interest in a border of 20x8ft evergreen mainly if possible they could be Hosta/ferns/grasses/hebes (that the extent of my knowledge) nothing that will grow more than 4ft
Here are some ideas below. You mention hosta and ferns, but they are only for shady areas, so I included shade plants, too.
The flowering evergreens in this article are more the size you want:
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-evergreen-trees.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-plants.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-8/zone-8-plants.htm
If they are still in pots I would move them inside to the garage till the threat of frost has passed.
I’ve planted two Sum and Substance hosta. Both have a large stem with a bulb or cluster of leaves at the end. Not sur if this is normal.
This can happen for a few reasons-
Diseased soils will produce spots such as this, but it can happen due to pH swings, or nutrient deficiencies, as well.
Too much sun can be damaging to the plant, as well. Make sure that these plants are situated in an area where they will receive quite a bit of shade. They will enjoy dappled light, but never full sun.
I would treat with a fungicide, first. This article will help:
https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
These articles will help you to test your soil, and care for the plant:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
https://www.gardeningknowhow.com/ornamental/foliage/hosta/growing-hosta-plants.htm
n thiere location. how do i prevent spreading what is damaging hosatas to other plants?
If your Hosta are in shade, as they prefer, the hens and chicks won't do well. They need sun and gritty soil. If your Hosta are in sun, the hens and chicks probably won't be bothered by snails and slugs, the biggest enemy of Hosta.
https://www.gardeningknowhow.com/ornamental/cacti-succulents/hens-chicks/growing-hens-and-chicks.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/organic-snail-control.htm
Hosta leaves have turned very yellow and look almost dead - is it too much water?
It could be too much sun. Most hostas need shade to part shade to do well. They are the stars of the woodland garden. Here are more causes:
https://www.gardeningknowhow.com/ornamental/foliage/hosta/hosta-leaves-turning-yellow-2.htm