Ok, take a look at the Sunny 16 rule. Assuming it is sunny and you've got a front lit subject, that rule states that at f/16 your shutter speed is 1/ISO. So if you are at ISO 100, your shutter speed would be 1/100. If you want a slower shutter speed, you need to close your aperture even more... but at f/16 you may be close to the end for your lens. You may have 1 or 2 more stops you can go to (f/22 or f/32) which means you can achieve a shutter speed of 1/50 at f/22 or 1/25 at f/32.
If you want to go even slower, you need to use a filter like a circular polarizer (typically two stops loss of light) or neutral density filters. Another option is to wait for a cloud to drop the light level or come earlier or later in the day.