What is the mature width of sweet pea bush?
My research shows that the average width of these is around 3 to 5 feet. Here is an article for more information on these shrubs:https://www.gardeningknowhow.com/ornamental/shrubs/sweet-pea-shrubs/growing-sweet-pea-shrubs.htm
All of my sweet pea shrubs (4) suddenly all look dead! Is this normal?
This is not normal! It would help to know where you are located and to have pictures. These are very sensitive to cool temperatures.
This article will give you more information on these shrubs: https://www.gardeningknowhow.com/ornamental/shrubs/sweet-pea-shrubs/growing-sweet-pea-shrubs.htm
I have been recommended petite butterfly sweet pea shrubs and company them with star jasmine. I would like to know about plant pests and flowering seasons or what plants would be most trouble free that you would recommend
Those are good choices for your area. As for plant pests... tey carry the same risks for the same pests as most plants. I will include an article for both plants, and a link to ways to craft your own pest controls that will help you here.
SweetPea Shrub: https://www.gardeningknowhow.com/ornamental/shrubs/sweet-pea-shrubs/growing-sweet-pea-shrubs.htm
Star Jasmine: https://www.gardeningknowhow.com/ornamental/flowers/jasmine/star-jasmine-as-ground-cover.htm
Organic pest control and overall garden health: https://www.gardeningknowhow.com/special/organic/
I would like to know why my sweetpea bush appears to be dying. Last year it was perfect. But leaves are now yellow, withering & looking very unhealthy. Friends aldo have the same problem with theirs.
Check for signs of pests, they may be very small. You describe symptoms of a possible infestation.
Neem Oil can be used on your plant.
https://www.gardeningknowhow.com/ornamental/shrubs/sweet-pea-shrubs/growing-sweet-pea-shrubs.htm
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
Some of them do. If you were told that they get that tall, then they are likely one of the taller cultivars. Some of them will be marked as "dwarf" or "mini" and they will be shorter.
Unfortunately, they require partial shade in the hot Summer months, and full sun when it cools off some in the Winter. With that being said, they will not do as well as they could in the spot you have described.
They will still grow and may do just fine, but they will probably not perform their best.
Here is an article that will help: https://www.gardeningknowhow.com/ornamental/shrubs/sweet-pea-shrubs/growing-sweet-pea-shrubs.htm
My pictures say it all. I even added a chop stick thinking they might need something thinner but they won't grab hold.
I notice that they are still too young to have developed tendrils for climbing, just yet. Once you notice the tendrils that protrude from the tips elongate, then it will begin to start seeking something to attach to.
These appear to be the ornamental Sweetpea, and not the edible Sweet Pea, also. Sweetpea, the ornamental, is poisonous.
Here is an article that will help:
https://www.gardeningknowhow.com/ornamental/flowers/sweet-pea/care-of-sweet-peas.htm
The hanging basket was left out and got flooded, thou I put holes in the plastic before planting they are changing colour and going a paler colour, got them in a green house at the mo due to bad weather again. Is it worth changing the compost to see if it helps them? They are about 4 inches tall at the moment.
Starting over will be the best, and fastest way to a decent flower set.Sweet Peas do not recover well from problems, and when they do, they will be in poor health not likely flowering well.
Make sure to use a container that already contains an adequate number and size of drainage holes. Change the soil and mix potting soil with compost to avoid overfeeding. Overfeeding peas will cause lush growth, but none of the fragrant flowers.
Here is an article that will help:
https://www.gardeningknowhow.com/ornamental/flowers/sweet-pea/container-grown-sweet-peas.htm