I just removed the carpeting from my stairs and refinished the treads and risers. The stairs have a 3' x 3' landing. To maintain the height of the stair riser, I plan on removing the 3/4 plywood and install 3/4 solid hardwood.

Would there be a problem if I installed the 3/4 hardwood directly on the joist on the landing?

Hardwood flooring should be installed with no more than 10 inches between floor joists or blocking. If 2X material is fastened on 12 inch centers then you should be OK. I recommend that each piece of flooring have two fasteners, minimum, so crossing two supports would be necessary. You may need to install more framing support before the floor installation. Use full-length boards for best results.

Assuming the stair treads are 1 piece or glued staves, how about the same treatment for the landing......glue up some 1 X hardwood boards. You can add splines to the edge joints for added strength. Use pieces long enough to span the entire landing.

Thank for the replies. I'm going to surround the existing 2x8 joists with (2) 2x6 board but lower them 3/4. Then cut the existing 3/4 plywood into that recessed space. So the platform with have joist and plywood on it before I install the hardwood

A stair landing does get concentrated traffic. If you cannot get full length boards which should be glued to the joists and fastened with nails stales or cleats, the plywood under the flooring is great.