Spurge (Pachysandra spp.) is an easy ground cover to grow under trees in the temperate United States. Two of the most commonly grown species are Allegheny spurge (P. procumbens) and Japanese spurge (P. terminalis). Both thrive in partial to full shade, in any fertile, non-alkaline soil that is not bone-dry. They grow moderately slow, sending out stem like rhizomes, and create an 8- to 12-inch green carpet.
Plant spurge in a fertile, crumbly-textured soil that is rich in organic matter; these conditions mimic the natural habitat of the woodlands in the eastern United States or eastern Asia where spurges grow wild. Rotted leaves, compost or well-rotted manure provide trace nutrients and help retain moisture in the soil. Continual leaf drop and other plant debris over the years increase the humus in the soil, and diminish the need for synthetic fertilizers.
Fertilize for Foliage
Although pachysandra plants do produce tiny clusters of white flowers in late spring, their main ornamental feature remains the evergreen foliage. Therefore, any fertilizer product with a balanced formulation, such as 8-8-8 or 12-12-12, suffices. Avoid fertilizers that are overly rich in phosphorous, which promote blooming.
Usually the fertilizer you apply around shrubs and trees sustains the spurges underneath them just fine. Apply the fertilizer in very late winter to early spring before new growth starts.
Follow Recommended Dosage
Since spurges grow under trees which strongly compete for water and nutrients, they often exist in dry topsoil. Whichever fertilizer product you use, follow the recommended dosage rates. Do not over fertilize the trees and shrubs merely to benefit the ground cover. The salts found in fertilizers can burn foliage and roots, especially if you apply the fertilizer when the soil is dry. Irrigate the soil deeply after you fertilize, since more soil moisture is required to offset the roots' absorption of the fertilizer salts.
Although scattering any general purpose, slow-release fertilizer atop pachysandra is usually adequate, a soil test provides more specific insight into the nutritional makeup of the garden soil. If the soil already contains plenty of organic matter and a natural abundance of nitrogen, phosphorus and potassium, you may not need to fertilize every year. If you do fertilize the spurge and growth is still slow or yellowish, increase irrigation to promote healthier plants, instead of arbitrarily pouring more fertilizer onto the soil.