Recommendation letters from professors in other fields

[SomeNerd]

Hello,

I am an undergrad. I will apply for Ph.D. stats fall 2019. I major in math. I am doing undergrad research with professors in geoscience (mostly laboratory work), civil engineering (machine learning with MATLAB), and math (computational, PDEs). Should I ask for recommendation letters from geoscience/civil engineering professors? My other option for rec letters would be math professors that can only talk about my grades. (I don't know if this is necessary since my grades are already shown on my transcript/GRE).

Thanks in advance for your comments.

[bayessays]

Definitely choose the professors that know you better if they'll say good things, especially because they're in the sciences anyways and two of the projects are related to statistics.  If you had three humanities profs, that would be different but you shouldn't worry at all. 

[SomeNerd]

Thank you bayessays for your kind reply!