Gardening Q & A:
Master gardener Paul James of HGTV's Gardening by the Yard
answers viewer questions about nutrients, ornamental grasses, coir, roots
and a report on his pond plants. Master gardener Paul James answers questions on a variety of
gardening topics.
Q. What's the difference between macro- and micronutrients?
A. Macronutrients include carbon, hydrogen and oxygen, which
are derived from air and water, as well as nitrogen, phosphorous, potassium, calcium,
sulfur and magnesium, which are absorbed from the soil. Micronutrients include
boron, chlorine, copper, iron, manganese, molybdenum and zinc, and they too are absorbed
from the soil.
Most synthetic fertilizers have only the so-called "big
three" macronutrients in them—nitrogen, phosphorous and potassium—and ordinarily
don't contain any of the micronutrients. Natural fertilizers tend to have a smaller
percentage of the big three, but very often they contain some micronutrients, especially
iron.
For proper growth, plants need macronutrients in relatively
large quantities and micronutrients in extremely small quantities. There's one
product that tends to have a nearly ideal mix of both macro- and micronutrients: compost.
Q. I once read that Miscanthus was sterile, but it's
spreading in my garden. What gives?
A. The hugely popular ornamental grass Miscanthus, also
called maiden grass, isn't sterile. In fact, they're borderline invasive in many
gardens. James has noticed in his own landscape that those growing in his lawn have never
reseeded, whereas those growing in more fertile garden beds have spread all
over the place.
Fortunately, the volunteer clumps are relatively easy to remove
with a firm tug while they're still young. Another potentially invasive
ornamental grass is Chasmanthium latifolium, better known as sea oats. Once
volunteers of this grass get a foothold in the garden, they're difficult to
remove without a fair amount of digging. You could, of course, remove the
flower stalks as they appear to prevent the grasses from spreading, but the
flower stalks are a key feature of grasses. Your only real recourse is to
routinely pull up or dig out the volunteers as they appear.
Q. Is coir a substitute for peat?
A. For the most part, yes, but coir—which is a fiber
extracted from coconuts—has a nearly neutral pH. Instead, peat has an acidic pH
of 3.5 to 4.5, which is why it's often used to amend soils in support of
acid-loving plants, such as azaleas and blueberries. Coir also has some
nutrient value, whereas peat is essentially sterile. If you blend coir with a
potting mix, realize that the plants you grow may not need as much fertilizer,
especially one high in potassium. Those plants may not need as much water
either because coir can absorb roughly 30 percent more water than peat.
Q. How damaging can it be to disturb tree roots?
A. It depends on the tree and how much damage you're talking
about. Some tree roots are very sensitive to disturbance, while others aren't all that
bothered by it. For example, most oaks, dogwoods, magnolias and pines are very sensitive
to root disturbance. On the other hand, the roots of crabapples, ginkgos, honey locusts
and pecans can withstand a fair amount of disturbance.
Regardless, you should try to minimize root disturbance when
working at the base of trees. Also avoid causing any damage to the tree's trunk
because these wounds can invite pests and diseases.
Q. I never can remember where to place my sprinkler for
optimum coverage. Any ideas?
A. Order a pizza! Those little tables that come in pizza
boxes are ideal for marking where to place your sprinkler. Just stab one in the ground,
and you'll never have to search for that perfect spot again.