The scheme is operated by the Tree Council, Woodland Trust, Trees for Cities, England's Community Forests, Defra, Groundwork, the Forestry Commission and local communities.
Pauline Buchanan Black, director general of the Tree Council and BTP partnership chair, said: "I'm expecting the numbers will go up significantly. We have 400,000 trees committed to being planted.
"We could have given the money away very quickly, but we need to have safeguards. There is money in the pot still."
A Woodland Trust representative said: "Applications closed in February 2011 so they've only had a few months planting and 100,000 trees in that time is pretty good going really, bearing in mind the application process time."
A Defra representative said: "More than 100,000 trees have been planted so far as part of the Big Tree Plant, and people have already pledged to plant another 400,000, so we're halfway to meeting our target."
The next application deadline is 14 March 2012. For further details, visit www.thebigtreeplant.direct.gov.uk