We have a very large yucca plant in our back garden with three main trunks on it. Each trunk has an additional two newer and smaller trunks growing from it. The plant has been in the garden over ten years. After the harsh weather and heavy amounts of snow, the leaves have virtually all fallen off and the top part of the trunk where the leaves are growing from has rotten. Some are black and some are just so soft and squisgy. We will be devastated if the plant cannot be saved, as it is the main feature of our garden. Can it be cut back and will it regrow? I am not a gardener by any stretch, so any help will be appreciated.
I would wait until spring to cut back the plant. It will help protect the new growth, just in case another freeze occurs. These articles will help you as well:
https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm
https://www.gardeningknowhow.com/plant-problems/environmental/tips-for-saving-cold-damaged-plants.htm
https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-cold-weather.htm
The pruning instructions here apply to outdoor yucca as well:
https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-plants-care-and-pruning-tips-for-pruning-a-yucca.htm
Outside Yucca got badly damaged in the heavy snow, leaves are brown and flopping around the stem.
I am sorry to hear that your plant was damaged. This article will hopefully help:
https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-cold-weather.htm
How do I know how much water and sunlight to give to a Yucca plant that is about four feet tall?
Most yuccas need bright light for several hours a day. Water the plants when the soil is dry to the touch.
I have a 7-trunked yucca about 3. 5 metres tall. It has flowered a couple of times and is starting to look a bit thin on top. Should I do something or just let it carry on?
You can try topping a few of the trunks to encourage thicker growth. This involves cutting off the top 1/3 of the branch (which you can root as a new plant).
Will my yucca recover from severe frost damage?
This article may help: https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-cold-weather.htm
We have two yucca plants outside our window growing together. How do I know what to prune? Do I remove all the brown leaves, and what's the best way to separate the two plants?
This article should help you with that: https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-plants-care-and-pruning-tips-for-pruning-a-yucca.htm
I cut a four-foot high yucca plant down to the ground. What will I have to do to the trunk that is left in the ground?
If you are trying to get rid of the yucca, then this article can help you with that: https://www.gardeningknowhow.com/ornamental/foliage/yucca/removing-yucca.htm