When to Use Woodchips and When to Use Rock?

The relationship between amending the soil at planting time, the choice of using woodchips as a surface mulch, or applying crushed rock instead, also relates to the types of plants found in your landscape. Of course, I like compost best to amend the soil at planting time, but other amendments will also work. Adding amendments to the soil does two things: it makes the soil “fluffy” (changes the soil structure by making the soil more porous) and adds whatever plant nutrients to the soil that it contains.

Chinese photinia is from where??? You guessed it, China. Plants not coming from the desert Southwest should be planted in wood chips and soil amended with compost.

What are rich composts?

Some composts are rich and full of nutrients, i.e., made from sources of manure. Other times they are not so rich, and the addition of a fertilizer might be needed. Some of the chemicals in the compost are “tied up” inside the compost and released slowly as it “rots” in the soil. Others are quickly washed into the soil with the first few applications of water. Some of these chemical additions can be good and some are not. It depends on what was used to make the compost. The only real way of knowing its chemistry is testing the soil through a certified laboratory or trusting the compost supplier.

This is an example of a "rich" compost, Viragrow's 166. It is full of plant nutrients, about $150 worth of plant nutrients in every cubic yard, but also contains biosolids. It's a tradeoff. Do you want to recycle your poop? You made it.

 

Planting amendments mixed with soil

Planting amendments like compost mixed with the soil at planting time, and then covering the soil with rock mulch, gives many plants somewhere between three and five years before the plant has problems (it doesn’t add the right kind of plant nutrients when it decomposes). By that time the soil amendment(s) used at planting time are gone. Plants sensitive to the loss of amendments respond by the leaves first turning yellow and scorching, followed by leaf drop, and finally followed by branch dieback.

This is also a compost from Viragrow. It is plant based and "organic"; it does not contain one iota of biosolids. But it is lighter in color, more coarse in texture and not as "rich" in plant nutrients. A fertilizer should be applied to the plants along with this compost.

Sometimes this process weakens the plants enough for insects like borers to finish the job. This is particularly true of plants like Photinia, Nandina/heavenly bamboo, Sago Palm, Japanese blueberry, Carolina Cherry Laurel, and most fruit trees.

Applying compost to rock landscapes.

There is a trick you can use if your landscape is already covered by rock. Rake back the rock to bare soil three feet away from these plants and apply a rich compost (or compost plus fertilizer) to the soil surface (even better if you lightly “scratch it” into the soil), water it in, and put everything back including the rock and irrigation. If the landscape area has rocks bigger than one inch, the rich compost can be applied on top of the rock and wash it in without raking the rock! It’s easier that way. If you have had yellow plants in the past, count on using this method every three years. You might consider adding your favorite iron to this application if it’s applied in the spring and these are iron critical plants.

General Rule of Thumb

When planting with plants from the desert Southwest, they can tolerate rock. When planting with plants not from the desert Southwest, use wood chips.