Use surface mulch that decomposes quickly around vegetables

Q: I use woodchips around my vegetables, fruit trees and landscape plants. When I turn it over after the first freeze, what should I add to counter the effects of rotting wood?

A: That is a drawback to woodchip mulch used around vegetables. Older information recommends straw mulch around vegetables, but that can be weedy, doesn’t rot very quickly and can be difficult to turn over and mix in the soil. Straw decomposes slowly in the soil.

Use woodchips on soil surfaces around plants that don’t need the soil turned over every year such as fruit trees and ornamentals. No need to turn it over. Woodchips rot from the bottom as long as they are in contact with wet soil. Replenish by adding it to the surfaces of these areas. Four- to 6-inch depth is ideal.

Better to use a surface mulch that decomposes quickly around vegetables and herbs like shredded newspaper, grass clipping and even sawdust. But my favorite is pine shavings sold for animal bedding. It is shaved pine mostly and decomposes quickly in moist soils.

Spread only enough to shade the soil surface and keep it cool — maybe a ¼-inch deep or a bit more. It dissolves in the soil quickly during warm weather. I use it to cover the soil surface when germinating seed or planting transplants in raised beds during the hot and warm months.

If you’re not vegan, used animal bedding is valuable because the nitrogen from the manure and urine is already mixed in it and prepares the wood shavings for decomposition. Otherwise, decomposing pine shavings gobble up some of the soil nitrogen when it rots. Not a huge problem, but this can happen if the soil is kept on the lean side from a lack of added nitrogen to the soil.

Did you know tons of horse bedding is taken to landfills in Las Vegas? Horse bedding makes a great soil amendment. These horse owners are looking for ways of getting it used rather than dumping it. Sounds like an opportunity.

Rake the woodchips aside when planting or replanting vegetables. Spread it back around the plants again after planting. You only need enough room to dig holes for transplants or for direct seeding. Once the plants are up and growing, the mulch can be put back.

Q: We have a serious nutgrass problem. You recommended Sledgehammer herbicide to control it. I’ve been online looking to purchase it but I keep getting directed to “Sedgehammer” products. Are they one in the same and did you just get the name wrong?

A: Nutgrass is not really a grass at all but a sedge. Sedge usually has a way of regenerating itself when it dies and nutgrass was no exception. It’s called nutgrass because of the underground nut that remains in the soil if the top was pulled off or killed.

Hold on. I will get to your question in a second.

Killing the top of the plant is easy. It could be killed with several types of weed killers, burned off with a fire weeder or removed with a hoe. But the underground nut causes a new plant to grow in its place.

Usually, not just one plant but two would regenerate from the nut to replace the one that was killed. With only those methods available, the only thing that works is to continually destroy the tops repeatedly until the nut is starved and gone.

This works but requires diligence. If you let the top grow back, it would rebuild the nut and you have to start all over. But nutgrass in lawns is still a huge problem because these methods also damage lawn grasses.

I worked with a chemical weed killer found to control nutgrass in lawns, without damaging lawn grasses, during the 1990s. This weedkiller was different than others because it killed the nut but had no effect on lawn grasses. It was given the name “Manage” by the manufacturer. The rights were later sold to a different company but the name changed to Sledghammer. Same product but a different name.

Repeat applications are needed when using Sledgehammer herbicide because not all the nuts are killed. The tops die but a few of the nuts survive and send up a new plant. Reapplication timing of the chemical is critical or the nut will re-establish.

You must reapply it when the new growth from nuts is young, about the four-leaf stage, or it will re-establish. If diligent, slowly you will extinguish the nuts and keep them from re-=growing.

I see it is available from Walmart and Domyown Pest Control online. Try entering sledgehammer and nutgrass and weed killer in your online search engine.

Q: I have several heavenly bamboo plants that are well-established in my yard. I recently noticed a lack of robust growth and signs of disease or pests or maybe both. I sent you some pictures. What do you think?

A: Heavenly bamboo, aka nandina, is not a bamboo and not even closely related to it. It sort of looks like a bamboo, hence its name. It comes from places where the soils have organics in them naturally — not from deserts and it does not grow well in desert soils.

In warmer climates, it may keep its leaves during the winter. Usually not in Las Vegas. It drops its leaves due to leaf damage from winter cold.

Heavenly bamboo does not like desert soils unless organics like compost are added to it and the soil is kept moist. So rock mulch and planting in a desert landscape with cacti is a no-no. That might work for the first couple of years, but then the plants slowly turn yellow, scorch, decline in health, drop their leaves and look bad.

The discoloration of the leaves, brown edges and yellowing are probably related to the soil degrading and losing its organics over time. My guess, it has gotten progressively worse over the years.

Heavenly bamboo comes from Eastern Asia where soils are rich and not deserty. When surrounded by rock, nandina declines in appearance, and its health takes a dive over time. Nandina looks good after planting because of stored food supplies inside the plant and amendments added to the soil. But these both disappear in a few years.

There does seem to be insect damage to the leaves, possibly by thrips. Thrips are very tiny insects that can fly only well enough to travel a few inches. Flower thrips like to feed on soft flower petals and other thrips on new, emerging leaves.

Leaf damage to nandina by thrips is a first for me in the desert so I had to do some digging in references. Fresh damage appears as water-soaked areas. Later on, these areas dry out and scarring or obvious surface damage appears as tiny brown or white spots on leaves.

If there is rock surrounding them, rake it back and work some compost into the soil surface as deep as you can and water it in. Replace the rock on the soil surface with woodchips. Water enough in one day so you can skip at least a day in the summer and more when its cooler.

Organic sprays such as Spinosad do a good job controlling thrips. Read the label.

Bob Morris is a horticulture expert and professor emeritus of the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.