Goals from Jason Gilchrist and Dean Winnard put an abrupt end to the Wood’s FA Cup journey for another season.
“I didn’t get my team selection right today. We made a couple of changes and I’ve got to hold my hands up on that,” Garrard told the club’s website.
“I don’t think I made the right decision on the selection but I'll learn from it and take it on the chin. It's just frustrating.
“They [Southport] were the best team across the park today and Jack Sampson in particular was unreal. He was unplayable at times.
“Our organisation was poor today and that really annoys me because that’s usually something we have a base on - We just looked so open at times.”
Wood fans who made the 360-mile round trip were treated to free tickets and subsidised travel by chairman Danny Hunter.
And boss Garrard had a simple message for the travelling supporters.
“I’d be livid as a Boreham Wood fan today because we didn’t have an identity today. I can only apologise to the travelling fans.”