As long as you can 
@mab6311 wrote:
suggestion on how long i should Garden?
As far as the score drop, I agree with above, you have three things at play, the appearance of a new account which lowered your AAoA, the addition of a new inquiry, and the high utilization. Once the utilization is paid down, there will be no lingering effect for the prior high utilization. You'll get all of those points back. But you may still have an effect from the new account and inquiry. That will fade with time, and eventually that new account willl help you achieve a higher score.
As for how long to garden, it completely depends on what your goals are. What is your score? Did it drop 20 points from 780 to 760? If that's the case, it doesn't matter at all. You don't need to garden if you don't want to. Do you have any major purchases coming up? Do you have baddies on your reports? Gardening has to be considered in context.
A person who has negatives on their reports and is trying to get everything in order for a mortgage app needs every last point they can get. That person needs to be extremely concious about adding new accounts and needs to be inquiry sensitive. But someone with a clean report doesn't need to obsess over AAoA and inquiries as much, especially if that person isn't planning on a big purchase anytime soon.
A lot of people who come to this site start from a position of credit rebuilding or credit repair. They just applied for a ton of cards, tanked their score, and then learn all about inquiries and AAoA. For those people, gardening can make a lot of sense. However, what happens, in my opinion, is there tends to be an overemphasis on gardening and raising your score just for the sake of a high score. People forget that inquiries only count for 10% and length of credit history is something like 15%. For clean reports, you can still have a great score with average AAoA and quite a few inquiries. So you get threads where people with ~800 scores freak out because an inquiry casued them to lose 15 points!!!
So all that said, what are you trying to accomplish. Do you still have scores above 700? If so, and you're not planning on a house or car purchase, garden however long you want to. If you see a credit card that you like or want to take advantage of a sign up bonus, I wouldn't worry about it. There's no hard and fast rule about waiting 6 months.
Starting Score: ~500 (12/01/2008)
If you're applying for a mortage in a year, I would stay in the garden until you have your mortgage out of the way. Especially if you are considering conventional where getting your score back up to 760 could make a slight difference in rate. After that, you don't need to worry so much about inquiries. You have great scores.
@ElCamino wrote:Part of your drop in score is more than likely due to the actual opening of the new account and the inquiry required for approval.
How many accounts did you have prior to the new card and how old were they? The thinner and younger your portfolio is, the harder a new account is going to hurt your score.
Given that your overall util is low, even with the charges on the new card, I can't see that being the sole reason for your score dropping.
This is correct, after you PIF you'll get probably half of those points back.
