Create another "Hue/Saturation" adjustment layer and double-click on the new adjustment layer's icon(on the left half of the layer row). The layer icon is a scaled-down image representation of the layer for normal layers, but they have specific icons for adjustment layer types. Make sure you double-click on the new, top-most layer, labeled "Hue/Saturation 2". Also, make sure you double-click on the the left half of the layer.



A palette with 3 sliders will pop up. Drag the saturation all the way to the left, or enter the value "-100". This will desaturate the photo, leaving it in black and white.



The image is now black and white, but you may want to fine tune it a little. Double-click on the layer icon(left side of the layer row) of the first "Hue/Saturation" layer, "Hue/Saturation 1."

The sliders will pop up again. Mess around with the "Hue", Saturation", and "Lightness" sliders until your are happy with the results.



You can selectively make Hue, Saturation, and Lightness adjustments to specific color groups; like "Greens" by going up to the field at the top of the "Hue/Saturation" dialog box(directly above the Hue slider) and selecting the color group you want to selectively adjust. You can selectively adjust the Hue, Saturation, and Lightness for each color group. So for this image, if you adjust the H/S/L for the "Greens"; you are only changing the green colors in your image.

You can see the adjustments in color by turning off the visibility of the second "Hue/Saturation" layer, "Hue/Saturation 2." To turn off the visibility of a layer, click on the eye icon to the left of the layer.