Why does my French Lilac that bloomed last year, now have no blooms and cupped leaves? There is another one five feet away that has some blooms and leaves with only a few cupped leaves.
It is probably a lack of phosphorus. Add a phosphorus rich fertilizer (normally sold as a "bloom boosting" fertilizer) to the soil. This article will help:
https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-bush-not-blooming.htm
My husband 'trimmed' back my beautiful lilacs three years ago, during the summer. I've had these bushes approximately 20 years and hate to take them out, but they look terrible. Can they be saved?
Your tree may simply be in need of some trimming. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/pruning-lilac-bushes-when-to-trim-lilac-bushes.htm
My lilac bushes seem to have a problem. Their leaves are turning black and shriveling as if it's got leaf curl. Could it be they need something in the soil?
It sounds like your lilac has lilac blight. This article will help with that:
http://plantclinic.cornell.edu/factsheets/lilacbacterialblight.pdf
How do you look after a new 5-foot white lilac tree?
The care is the same for purple varieties. This article should help: https://www.gardeningknowhow.com/ornamental/shrubs/lilac/lilac-care-growing-and-planting-lilac-bush-plants.htm
My lilac is planted in the ground, but I have a new, very large deck and very large pots and I would like to have my lilac where we can be closer to the aroma.
You can plant any shrub in a container as long as you provide it enough space for the roots and enough water. If you would like a patio lilac, I would recommend looking for dwarf varieties as these stay smaller and make it easier to provide they water and root space they need.
Also keep in mind that plants in containers experience conditions that are one zone lower than yours because they are not insulated in the ground. So, if you live in zone 5, you need a lilac that is tolerant to zone 4 if you plan on growing it in a container.
How deep do the roots go, and do they spread all over?
They go down a few feet, maybe 2-4', depending on how established it is.
The roots will spread about as wide as the canopy of the bush.
I was told that you can grow a lilac tree/bush by just using a clipping from the bush itself. Is this true? Our neighbor has the most beautiful DEEP PURPLE lilac flowers and I would like to try and grow a bush on our property. My sister lives in Minot, North Dakota and I would like to send her a clipping if this can be done.
Yes, this can be done. This article will help:
https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm