Question
I have an old lawn that's in big trouble from crabgrass and thatch.  I live in northern NJ (Zone 6) and I plan on reestablishing the lawn this fall.  I have found a few suppliers of liquidd dethatchers (enymatic digestors)online, but I would like your thoughts on their use versus mechanical dethatching.
 Thanks

Answer
There are no such thing as liquid dethatchers except the name. The industry is not regulated and you can call your product whatever you want. I have also seen no-mowing-needed lawn grass sold, but it does not mean that it performs as stated. There are obviously a wide range of opinions on the matter ranging from almost fanatic belief in the so-called liquid dethatchers to the comparison to "snake oils" and I am much closer to the latter.

If you have bad thatch, have a landscaper dethatch or core aerate the lawn. You can also rent the equipment and do it yourself.