Q: Can I use dehumidifier water to water my potted plants in the house and on the patio? I have heard this water is very pure, so would it be OK for pets? And what about cistern water? Folks used to use it for drinking water. I'm curious as I've heard some say cistern water isn't safe.
A: Dehumidifier water is excellent for plants, but it may not be the best for pets (and most certainly not people). Since the water is extracted from the air, it has no salt or calcium carbonate, which may be in drinking water, and when too high, are considered detrimental for plants, especially if used over a long time. Calcium carbonate is quite common from well water, and the pH of the water is often high as well. Water from a cistern has a similar benefit to dehumidifier water as rain doesn't pick up salt or calcium carbonate.
Both rain water and dehumidifier water pick up impurities from the air. Rain is especially prone to pick up dust and pollen. These will tend to settle out in the cistern. For a dehumidifier, all one needs to do is look at the stuff that accumulates on the evaporator coils (which are supposed to be cleaned every so often for the machine to work well) to realize this water isn't "pure" for people. Dust and other air impurities accumulate and the water drips across it. This water is likely OK for an outdoor dog that drinks from a stream or other sources, but I'd avoid using it for indoor pets.
As far as the safety of cistern water, first understand the cistern needs to be kept dark. If the water is exposed to sunlight, then algae and other organisms will grow as this water contains nutrients from the pollen and dust that wash in. To consume the water, it would be better to filter it, but cistern water may not pass the modern safety standards of potable water. If people "grow up" drinking well water or water from other sources that doesn't pass as potable, they build up resistance to any microorganisms in it. If given to someone who hasn't been exposed to this water, they may get sick.
Q: I have roots surfacing on one side only of a tree professionally planted four years ago. Should I scrape back the weathered mulch, cover with soil and the cover with new mulch?
A: You don't need to unless you want to. You can just top with more mulch if that is easier. If you want to keep the soil level and not have roots above ground, then you could do as you describe. But if you do this, apply as little soil as needed to cover the roots. Soil piled up around the base of the tree can smother the roots below. So only apply where the roots are exposed and not to the other side of the tree. We encourage folks to have a mulch ring around a tree of about 5 feet in diameter for a small to medium size tree.
Q: I have a houseplant that has these little gnats hatching out. What are they, and what can I do to get rid of them?
A: They are likely fungus gnats if they have a wispy way of flying; if these fly quickly then they may be shore flies (similar to a tiny fly). Both are attracted to algae and moss, so if the plant will tolerate less water and fertilizer, then hold back on fertilizer and let the soil surface occasionally get dry. You can try to knock back the algae by mixing one-part water to one-part 3 percent hydrogen peroxide, the typical household concentration. Place plant in sink and let it drain completely. Placing rocks over the surface of the soil will also suppress algae growth, but then it is harder to tell when to water the plant. The aesthetics of an attractive layer of rocks can be appealing.
Q: Will your Master Gardener class be held for sure? What's the deadline to sign up?
A: We will hold it if we get 12 signed up, and we are a few short of that. We need to make a decision on whether to hold it by Aug. 22. We'll hold registration open until Aug. 25, but we need 12 by Aug. 22 or we'll cancel it and direct folks to the online class if they don't want to wait a year. We are the only class in the area this fall. The cost is $150, and please contact our office ASAP if interested. It runs from 6-9 p.m. Monday evenings for 13 weeks.