Drought Tolerance, Sheet Mulching, Liquidambers and Bamboo

Q. I’m looking to remove a portion of my lawn and replace it with drought tolerant plants. Is there a way, I can do this without removing the grass or using any chemicals to kill it? In addition, I don’t want to wait for the grass to die first.

A. Yes, there is a method of doing exactly what you described. It’s called ‘Sheet Mulching.’ Sheet Mulching is not new, and in fact it’s used by organic gardeners who utilize Permaculture. Permaculture is a philosophy of working with, rather than against nature. It’s a natural process that combines soil improvement, weed removal, and mulching in one fell swoop. It is currently being utilized by a whole new group of gardeners looking to replace their grass with plants. You’ll need cardboard and/or lots of newspaper along with an organic mulch.Stack of newspapers

First, scalp the grass by mowing it as low as possible. Next, dig the planting holes, amend the back fill, plant your plants and add starter fertilizer. A thick layer of cardboard and/or a half an inch of newspaper should then used to cover or smother the old lawn area leaving the plants exposed. A second option is to cover the entire area first before planting, and then cut holes in the paper or cardboard layer. Think of the cardboard or paper layer as an organic or biodegradable landscape fabric.

To prevent the material from moving or blowing around wet the layer down as you proceed. You should over lap the seams or edges by four to six inches to prevent any new growth or weeds from developing. BE WARNED: Sheet Mulching will not prevent germination of the weed seeds that blow in on top of the mulch. Wet the paper again with the existing sprinklers before applying the mulch because the moisture aids the decomposition. I recommend converting conventional sprinklers to drip irrigation, and then cover the area with a three inch layer of mulch and wet it. Be careful not to bury the new plants in the mulch! The entire conversion process should take a about day once all the materials have been secured.

Sheet Mulching’s other purpose is to turn barren or unproductive hard soil into new planting areas. This can be done in the open ground or within a raise bed. It will take several growing seasons for the whole process to be completed, but it is worth the time and energy. To revitalize your soil, first place a thick layer of cardboard and/or newspaper on the ground. Next, top it with eight to twenty-four inches of organic material, bark, straw, grass clippings, along with household kitchen waste. Spread the material evenly in alternating layers. Start small, as you’ll likely need a significant amount of organic material. This technique is often referred to as ‘Lasagna Gardening.’

Liquidambar Trees and Pollen

Q. When a Liquidambar starts to produce pollen? I’m trying to figure out if it could be the source of our daughter’s severe spring allergies. Help!

A. Liquidambar trees bloom in March. It produces both male and female flowers as two separate structures about the same time as the leaves are emerging from dormancy. Plant pollen moves around by insects and the wind. Wind pollination requires light pollen and lots of it that can travel great distances. This is the troublesome kind because it is abundant, easily inhaled and likely to cause allergic reactions. Flowers that depend on bees, wasps, butterflies, moths and beetles for pollination tend to produce heavy, sticky grains that are somewhat airborne. My gut feeling is that your Liquidambar is not the culprit.

Instead, there may be multiple sources based on the plants in your yard. Foundation plants, especially next to windows and doorway entries, can be an immediate source of problems to those predisposed to pollen allergies. Birch, Oaks, Cedars, Walnuts and Olives, as well as Junipers, Privets, Podocarpus and even Lilacs are problematical for those allergic to pollen.

My suggestion is to purchase a copy of Tom Ogren’s book Allergy Free Gardening. In Tom’s book, he has developed a system of rating plants based on allergy severity and sensitivity. The Ogren Plant Allergy Scale (OPALS) assigns plants, including edibles, a rating from 1 to 10, with 1 being the best for allergies and 10 being worst. Hopefully you can now identify the problem plant(s)! Of course, this assumes that you know the names of the plants in your yard. If not, take samples or high-resolution pictures to your favorite garden center and ask the nursery professional for help.


‘Hellish’ Heavenly Bamboo

Q. My Heavenly Bamboo plants are out of control. They’re small towers, standing about six feet tall and are quite top heavy, which causes the branches to sag away from the plant at extreme angles. Is there a problem with severely pruning them back to a much smaller size? In my neighborhood, I see several plantings that are much smaller.

A. The Sunset Western Garden Book describes Heavenly Bamboo, Nandina domestica, as a slow to moderate growing shrub six to eight feet high, spreading three to four feet. It has a clumping habit and spreads by shoots or runners. There are several options you can use to control the top heaviness and the spread. You can: stake the clump and tie the staggering stems to it with green plastic tape; cut off the top-heavy or all the canes at ground level as new shoots will appear from the base. The new growth can be sheared annually like a hedge to keep it the right height. You can also reduce the tree’s width by removing a section of the clump with a shovel. Finally, your last is too replace them with the shorter growing varieties. Nandina Domestica Firepower, Harbor Dwarf, and Sienna Sunrise are three varieties that do not grow beyond four feet. Heavenly Bamboo does not produce lateral shoots, so reducing the height is the best way to obtain a more shorter and compact plant.