Garden docs: What is biochar?

Ken G. of Windsor asks: What’s biochar? I overheard someone talking about trying it in their garden. I couldn’t get any details.

Basically, biochar is organic matter that is burned slowly, with a restricted flow of oxygen. The fire is then suppressed when the organic matter reaches the charcoal stage. Very different from the tiny pieces of ash, coarse lumps of charcoal are full of crevices and holes, which help them to serve as life rafts for soil microorganisms.

The carbon compounds that are in charcoal form loose chemical bonds with soluble plant nutrients so they are not washed away by rain and irrigation. Biochar alone added to poor soil has little or no benefit to plants. But when it is combined with compost and organic fertilizers, it can dramatically improve plant growth while also helping to retain valuable nutrients in the soil.

One method of making biochar involves piling up some woody plant debris in a shallow hole in your garden bed. Burn the brush until the smoke starts to thin, then dampen down the fire with about an inch of soil and let the brush smolder until it is charred. At that point, put the fire out. The leftover charcoal will improve the soil by improving nutrient availability and retention. Since 2009 the Sonoma Ecology Center has headed up a project called the Sonoma Biochar Initiative (SBI) to promote the education, production and use of biochar in Sonoma County. For more information visit sonomabiocharinitiative.org.

Lori C. of Santa Rosa asks: I have a difficult time watering my indoor seed trays in a timely way indoors. The soil dries out too quickly, and sometimes I don’t get any germination. Is it OK to cover my seed trays with clear plastic to help keep the soil moist longer, or is that a bad idea?

Covering your seed trays and pots with clear plastic wrap will create a mini greenhouse effect and will help keep the soil moist longer. Just remember to remove the plastic once the seeds have sprouted because, otherwise it will promote disease seedlings. Once the plants have produced their true leaves, the soil needs to drain to encourage the roots to grow downward and to allow for air circulation.

If you are not going to be around for a few days, you could put the plastic back over the trays or pots but prop it up with some skewers or chopsticks at the corners and drape the plastic over the top. This will help buy some time in between waterings. Be sure the plastic doesn’t come in contact with the plants.

Sharon O. of Santa Rosa asks: Should I be cutting back/down, my deciduous grasses such as Miscanthus and Calimagrostis?

All ornamental grasses that are not evergreen should be cut back 3 to 4 inches from the ground. New shoots will then be able to sprout unhindered by any taller dead stems and dead blades.

In winter the dead stems and leaves provide some protection for the crown of the plant, preventing winter injuries. You can wait until very early spring to cut them back. Once they start to sprout, the dead stems are simply in the way of the new growth.

Do not cut back evergreen species at all. Simply remove any dead leaves and stems with your hand, (using gloves), or gently rake them out with a leaf rake. If you do cut back evergreen grasses, the cut stems won’t regrow, and will slowly die back.

Now you will have a plant that has half dead and half live growth, making for an unattractive grass.

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to them at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in Sonoma Home and pressdemocrat.com.