I have been given some summer snowdrop bulbs which still have the foliage on them. Can I plant them now, or dry them in the sun and plant them in autumn?
Snowdrops tend to dry out and should be planted out right away.
I would trim away some of the greens just to help in the planting, but leave as much of the greens that you can. The foliage dies away naturally and this feeds and give the bulb energy to store.
Here is an article with more information.
When snowdrop bulbs go dormant in late spring, do they lose their green leaves?
This article will help;
https://www.gardeningknowhow.com/ornamental/bulbs/snowdrop/information-about-snowdrops-and-when-to-plant-snowdrop-flower-bulbs.htm
What soil to plant them in?
Here is an article that will help you.
I usually have a good display of flowers on my snowdrop plants but this year the flowers have come up but then disappeared. What can be taking/eating them, please?
You can fertilize the bulbs after blooming to help them.
When you began to notice less flowers, this is the sign to lift and divide the plants.
Do this after blooming, they generally will fall apart, divide and plant right away.
Can I plant snowdrops now, i.e. in April?
This depends on where you are located. This article will help you in the meantime: https://www.gardeningknowhow.com/ornamental/bulbs/snowdrop/information-about-snowdrops-and-when-to-plant-snowdrop-flower-bulbs.htm
I have several Snowbells planted along my concrete driveway and they have been there for years and years. This spring they seem to have spread to the other side of the driveway.....lots of them! Do they propagate by seed? And why do you think they crossed over after all these years?!!!
They have likely crowded their area, and have started expanding, both in roots, and by seeds. Boiling water can control these in areas that you do not want them without making your soil toxic. Just be aware that this will kill any plant that it comes into contact with, so avoid any plants that you want to keep around.
My snowdrops are in bloom and have come up thru the leaves that fell last fall but I am wondering if I should rake the leaves off of them or leave them alone until after they bloom?
I would leave them alone until after blooming, or you may disturb them too much. This article will give you more information non the care of these: https://www.gardeningknowhow.com/ornamental/bulbs/snowdrop/information-about-snowdrops-and-when-to-plant-snowdrop-flower-bulbs.htm