Suncalc dot org -- link below is to suncalc where I'd typed in the address for the Washington Monument. You can type in your house address, specify the day of the year, the time of day, etc. Lots of fun.

suncalc.org

It shows the position of the sun and its relative height in the sky, you still have to use your imagination to see where the resulting shadows will be.

If you have trees or other things that cast shade, it's a complicated matter. So one of the more straightforward ways is to just go out and look. Draw where the sun is on a map of the garden, and write down the time. Go out a few hours later, and do it again. Understand that the sun pattern is going to change with the seasons, and plants don't necessarily read their press releases.

I know of no tool that can give a detailed photographic representation of shadows cast on anyone's individual property. @nickel_kg's Suncalc is a good tool, but it requires you to be able to visualize the corresponding effects. @mad_gallica's recommendation is a better practical reference.

Ideally, you would stand in exactly the same spot at least once a month to take a picture at the same time several times during the day. For instance, you stand at the curb in front of your home and take a wide-angle photo at 8:00 am, 12:00 pm, 4:00 pm, and 6:00 pm on the 1st of each month. Save the photos in a time progression for future review. Do this for the back yard and anywhere else you want. The more often you take photos, both monthly and daily, the better the progression will be at helping you understand how sun and shade is impacting your property.