When Dan Hinkley, co-owner of Heronswood Nursery in Kingston, finished his first perennial border, he was proud of it.

Now he sees the problems: All the plants were the same height. The foliage was all the same size. Leaf color varied little. He now understands that through contrasting and repeating height, texture and color of foliage, you can add drama to your garden. Hinkley shared his experiences earlier this month in a lecture at the University of Washington.

Height differential is a principle Hinkley calls "exclamation." This important element in floral design carries over to garden design.

Adding a tall plant that breaks up a line of shorter plants creates a more interesting composition. A few of his suggestions: An upright Japanese holly, Ilex crenata 'Pyramidalis', adds a dark evergreen vertical line, as does an upright yew, Taxus baccata 'Beanpole.' New Zealand flax (Phormium tenax) has sword-shaped leaves, can reach 6 feet and offers a range of foliage color. A striking perennial, Lobelia tupa reaches 8 feet, bringing vertical accent and, from June to November, red flowers.

Hinkley calls his second principle "accentuation," which involves bringing large-leafed plants to a composition to add contrast and drama to a garden.

One of his favorite large-leafed perennial plants is the umbrella plant (Darmera peltata). Ornamental rhubarb (Rheum palmatum) has several cultivars, but the straight species has the largest leaves. Hinkley also suggests Japanese banana (Musa basjoo), which adds large leaves and height to a garden design.

Adding foliage color to a design is what Hinkley calls punctuation. Take the golden English oak (Quercus robur 'Concordia'), brightly colored trees Hinkley says he can spot in the arboretum from a jet. Deutzia setchuenensis, with its gray leaves and long white blooms, and golden grasses such as golden Japanese forest grass (Hakonechloa macra 'Aureola') are good punctuation marks, too.

Repetition and contrast of these elements draws a composition together. Repeat a tall plant along a border, contrasting it with lower plants. Be sure to space tall plants so they stand out instead of clumping together.

Hinkley says he thinks about the design for a year before he puts a garden together. He makes sure to include foliage of different textures. He says he doesn't always get it right the first time.

Phil Wood has a degree in landscape architecture, and designs and builds gardens. Call 206-464-8533 or e-mail thegardendesigner@seattletimes.com with your questions. Sorry, no personal replies.