What should I do with my dahlias before winter? I live in the Pittsburgh area of PA. I planted them from seed and I've never seen plants explode in growth like them. I really love them but don't want to dig them up. Should I cut them down? If so, to what height?
Unless you live in an area with mild winters, you need to dig up your dahlias. Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/bgen/storing-bulbs-in-south.htm
https://www.gardeningknowhow.com/ornamental/bulbs/bgen/preparing-bulbs-for-winter-how-to-store-bulbs-for-winter.htm
Should I dig up my Dahlia tubers and store them for winter or leave them in the ground?
Unless you live in the south where winter temps are milder, then you should dig up your dahlia tubers. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/bgen/storing-bulbs-in-south.htm
I live in MI. We have already had one light frost, and my dahlia bushes are still budding. I need to know if and when I should cut the plants back for winter and how much to trim back?
Tender bulbs, such as dahlia, actually require lifting each fall and overwintering indoors in cold regions like yours. Only in warm, southern regions can these bulbs be left in the ground year round. They can be easily lifted with a garden fork or spade shovel prior to the complete die out of their foliage. Break up the clumps and separate the bulbs, allowing them to dry out some before storing, usually about a week or two in a cool, dry area. Then, clip off the foliage, shake off any remaining soil and pack the bulbs in dry peat moss or wood shavings within a brown paper bag or cardboard box. Place them in a dark area with cool room temperatures, like a basement, until spring.
I recently noticed a few very tiny little green specks on one of my new dahlia blooms. I didn't think much of it. They almost looked like dirt or pollen they are so tiny. I recently placed my potted plants into a new small starter green house I just built. Upon inspecting them this morning, I see a lot more of these tiny green specs on my newly opening dahlia buds. I am assuming these are some kind of bug. I removed that plant from the greenhouse and sprayed it with a strong stream of water. I noticed only one other dahlia plant in there has a few brown tiny specks on it. I removed that plant as well. What are these tiny bugs and how do I get rid of them?
They could be a few things, but aphids or mites are the most likely. I personally like neem oil. It is very effective on pests but harmless to people, pets and beneficial bugs. Here is more information:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
I have some dahlias and some begonias in my garden. My question is, do I HAVE to dig up my bulbs and take them inside in the dark for the winter, or can they be left in the garden?
Unless you live in an area with mild winters, you need to dig up your dahlias. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/bgen/storing-bulbs-in-south.htm
https://www.gardeningknowhow.com/ornamental/bulbs/bgen/preparing-bulbs-for-winter-how-to-store-bulbs-for-winter.htm
This article will help you with your begonias: https://www.gardeningknowhow.com/ornamental/flowers/begonia/wintering-begonias-overwintering-a-begonia-in-cold-climates.htm
Dahlias leaves are turning yellow, but flowers are still in bloom.
Yellow leaves can happen for a number of reasons. When did you last fertilize? Too much nitrogen can eventually cause the plant to yellow and start to die. If you have not fertilized, then underwatering, lack of nutrients or a fungus may be to blame. Increase water a bit, use a balanced fertilizer on the plant and treat it with a fungicide. This should take care of the most common causes of yellowing.
You may also find this article helpful:
https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm
I have some dinner plate dahlias that are about 5 feet but all the leaves are at the top. The bottom 2-3 ft are bare. Can I cut them back to 6-8 inches and will they come back more full?
I would not at this time, but for next year, you may want to pinch the tops while the plant is still small. This will force the plant to grow fuller. At that height now, cutting back that much would hurt the plant. It is best to stake them up this year and pinch them next year.