Mondo grass (Ophiopogon japonicas, also known as monkey grass or fountain plant) is a very small Oriental lily, though it resembles clumping ornamental grass with strappy, dark-green leaves. It grows well in part to heavy shade, and is often used as an alternative to lawns in shady areas of the yard.
Little to None
The beauty of mondo grass is how maintenance-free it can be. It tolerates not only bogs and occasional droughts equally, but can tolerate poor soils with little to no natural or chemical fertility. Don't fertilize much, and don't fertilize often, since much of the fertilizer will likely be lost to leeching when the roots don't absorb it. If the soil is already good quality, you can skip fertilizer altogether.
Fertilize with a balanced fertilizer in poor or depleted soils. Horticulture Avenues recommends a balanced 10-10-10 (Nitrogen-Phosphorus-Potassium) granular fertilizer. Organic fertilizers such as fish emulsion and kelp help green up the leaves and get it going after transplanting. If you have exceptionally poor soils, amending with manure, compost, hummus or alfalfa meal will help not only feed the grass but improve soil texture.
Amendments should be mixed into the soil before planting, since top-dressing around the small clumps can be time consuming. Apply granular fertilizers after mondo grass is established. If you're fertilizing as a part of your lawn fertilization regime, make sure that you water the granules off the leaves before they burn the plant. Liquid organic fertilizers may be applied any time the plant needs a boost. However, avoid applying liquid fertilizer during the heat of the day in the summer, when the moisture left on the leaves combined with sunlight can damage the leaves.
Dwarf varieties of mondo grass work well between stepping stones, but use care when fertilizing them. Right after fertilization, mondo grass will put out new, tender leaves that are more susceptible to foot-traffic damage. Many fertilizers will also discolor your step stones, especially granular varieties that are not swept off before water is applied. In this case, amending the soil before planting is better than trying to fertilize dwarf mondo grass after the fact.
More often than not, mondo grass is used as a border planting or as ground cover under a tree or bushy area. If you're fertilizing the plants next to the mondo grass, any over-spray, runoff or leeching area of the fertilizer will give mondo grass more than enough nutrients to work with.