Frogs and Frost Lines?
Boulder County Colorado
First off, you need to know if you have toads or frogs as they have there own unique set of requirements. With that being said, it is hard to know if the critters you relocated will actually stay in your garden bed over winter. If the conditions are right, they may, but if the conditions are wrong, they might move along to find a more suitable habitat. You are right that most frogs and toads spend the winter below ground, typically in very moist, sometimes muddy conditions near "their" pond. On the chance that they have stayed around your beds, I would say avoid tilling, just to be certain no one gets hurt.
I would also contact a biologist to get more information on the toads/frogs and you can start by trying to ID what you have so that you can let those professionals know what you're dealing with. Here is a link to ID CO toads (not frogs):
Below are answers to similar questions through this site:
"Frogs and toads are cold blooded, and being such, their bodies are the same temperature as their surrounding environment. This presents a problem in winter... if they stay active, they become "frog-cicles". Most frogs and toads solve this problem by burying themselves into the mud at the bottom of ponds during the colder months. Their body activity slows way down and they stay in this hibernation until the weather warms up. Many species of frogs and toads are quite cold tolerant though. Some of the first frogs to emerge from hibernation are the common Spring Peepers you hear in late winter / early spring. As a side note, some species of frogs have a special chemical in their bodies that allow them to freeze solid and then thaw at a later time with no ill effects."
"There are a number of things that can be done to help your frogs survive the winter. 1. Ponds must have 1-2 feet of mud at the bottom in order to provide a place for the frogs to winter. Additionally, the ponds must be deep enough so that even in the harshest winter there is 1 foot of water below the thickest ice. You can determine the frost line in your area by contacting a plumber and asking how deep do pipes have to be laid to prevent from freezing. Your pond needs to be one foot deeper than that frost line with the mud extending below that. 2. If you lack a suitable substrate, yet still have sufficient depth, you can make a mud bottom by mixing 1/3 sand, 1/3 crushed stone and 1/3 dirt and spread it on the bottom. 3. Removing large fish will also be helpful as they will predate on the frogs. 4. Don't do anything that will add heat to the water (ie. to prevent freezing of the water)."