Ask Mr. Smarty Plants

The name Mock Orange is a common name that is applied to several plants, but the plant that you have may be Philadelphus lewisii (Lewis' mock orange).

It would be a shame to remove a 5 year old plant that seems to be growing well, except for a lack of flowering. Before digging it up, lets examine one more thing; fertilizing. There are plants whose flowering is inhibited by an imbalance in the the nutrients that are available in the soil, particularly the ratio of nitrogen to phosphorus (N/P). Too much nitrogen may result in poor flowering. If the plant has been getting regular lawn fertilizer which often has a high N/P ratio, this could account for the lack of flowering. Lets look at fertilizer a bit more closely.

The most common elements that are found in fertilizers are nitrogen (N), phosphorus (P), and potassium (K), and fertilizers containing these three elements are termed complete fertilizers. Fertilizers differ in the relative amount of these elements that they contain, and this information is found on the label of the fertilizer container (bag, bottle, etc.) It is represented by three numbers eg 1-1-1, or 5-10-5, or 3-1-2, which are the percentages of the elements; N, P, and K in that order. This link from The Great Big Greenhouse and Nursery  can tell you a lot more about fertilizer.

Here are two links to Washing State University Extension; the first  is simply titled FERTILIZING, and the second is FERTILIZING LANDSCAPE TREES AND SHRUBS.

This link to Central Texas Gardening has some good tips about proper use of fertilizers.

For some help closer to home, you might want to contact the people at the Washington Native Plant Society.