The phrase "gradually gather" is correct and usable in written English.
You can use it when you want to refer to something that accumulates gradually over time. For example, "As the weeks passed, his courage began to gradually gather."
Mitchell Marsh's prospects looked excellent but concerns over Michael Clarke continued to gradually gather.
We gradually gather that their father is dead and their mother has disappeared – she suffers from mental illness and might even have committed suicide.
Other traits also irritate: between the electronic engine control and the six-speed automatic gearbox, the car was painfully slow to respond; flooring the accelerator caused it to pause and ponder, then gradually gather speed -- not the stuff of enthusiasts' dreams.
These toxic substances can gradually gather in the living bodies through the process of food chain, thus causing harm to human health.
Weak and imperfect at first, they gradually gather strength and perfection; they have their periods of infancy, they become old and then they die like them" (see Berti 1988).
Subjects responded first by decreasing the rate of increase of contact force at a latency of 50 ms and then by more gradually updating the motor command after 150 ms. Our goal was to use the experimental results to infer the basic steps that the system normally uses to gradually gather somatosensory information while continuously updating motor commands.
His profile as a bandleader, while still modest, has gradually gathered steam.
Morozov and other enthusiasts gradually gathered enough information and experience to enjoy their new hobby.
Over the past decade, 20 of the 28 rooms in the school have gradually gathered dust as the student population at Sree Karpagavalli dwindled to 225, one third of the 720 students who attended in 2000.
Reclusive artists like Jandek and Mr. Moore used to be at the mercy of their own idiosyncrasies — they gradually gathered far-flung fans by mail or in the dusty corners of specialty record shops, or not at all.
Agulodiek is a patch of land where families gradually gathered of their own accord, while Elay is part of the Ethiopian government's contentious "villagisation" scheme that ended last year.
