[Tamlin]

Glad I could help. For future reference, here's a quick rundown of how to do it:

1. Create a new layer (this isn't essential, but I usually like to keep everything on separate layers if possible).

2. Select white as your foreground colour.

3. Select the Brush tool. From the Brush drop-down menu, select Reset Brushes to load the default brush set (if it isn't already loaded).

4. Choose the Grass brush. Make sure Mode is Normal and Opacity and Flow are both set to 100%.

5. Press F5 to open the Brushes palette.

6. Click on Brush Tip Shape and then type -90 in the Angle box.

7. Click on Scattering and type 8 in the Count box.

8. Make sure that Color Dynamics is unchecked (otherwise your grass shapes will be varying shades of grey).

9. Position your brush in the top left corner of the image and click.

10. Position your brush in the bottom left corner, then hold down the Shift key and click again. The whole of the left edge of the image will now be overlayed with a line of horizontal white grass shapes. You can fill in any gaps with single clicks of the brush tool.

Obviously, the brush can be rotated to draw a similar border on any of the other sides - just change the value in the Angle box in step 6. Bottom border: Angle 0°, Top border: Angle 180°, Right border: Angle 90°.