Clean the garden cart to remove all the dirt. Wash it using soap and water. Dry the surfaces completely with a towel.
Sand any areas that are worn or rusted. Remove the damage. Paint the body of the cart using an exterior acrylic primer using a 2-inch paintbrush. Paint the cart when the temperature is moderate and out of direct sunlight. Allow the top to dry. Turn the cart upside-down, and paint the bottom. Allow the cart to dry completely.
Paint the body of the cart using a colored paint you like. Use the same brand of paint you selected for the primer so the paint adheres well. Paint the top and bottom until you are satisfied with the appearance. Some carts may require more than one coat of paint. Allow the cart to dry for 24 hours.
Sketch a design on paper, such as flowers, vines, plants, garden animals, words, lettering, numbers or any other design you like. Transfer your design to the front and sides of the cart with pencil.
Paint the design onto the exterior of the cart using artist's acrylic paints. These are available in a wide variety of colors. They are sold in tubes at craft and art stores. Use a round artist brush to create soft shapes, easy vines and fine details. Allow the paints to dry for 24 hours. Spray the surface of your cart with a non-yellowing clear-coat paint designed to cover acrylic paints.