Q: My variegated rubber plant loses its lower leaves and just when I'm ready to throw it away, gorgeous pink leaves open on every stem during this cold, cold Fargo weather. Is there any way to keep those lower leaves from falling off? - Mary Jo McClellan, Fargo.
A: Knowing a houseplant's native habit and form give important clues to their preferred care and habit. Rubber plant, Ficus elastica, including its variegated form, is native to India, Burma, Malaysia and similar tropical regions.
Rubber plants become tree-like in nature, so the natural tendency is to shed some lower leaves as they age. Increasing humidity can help tropical plants retain lower leaves longer. Place plants on water-filled pebble trays with the pot's bottom above water level, or mist frequently. Keep away from drafts, both hot and cold. Plants in groupings appreciate shared humidity.
Increased light can help maintain lower leaves. Monitor closely for insects, as spider mites can populate lower leaves, contributing to leaf drop.
Q: We've been saving coffee grounds, and some time ago you suggested uses. Could you mention them again? - Betty Bigger, Frazee, Minn.
A: Coffee grounds are an organic material that improves soil condition and can help prevent houseplant soil from becoming hard-packed. Tests have shown coffee grounds are neutral in pH. The acidity is leached out, percolating down into the coffee we drink. There might be a slight benefit to acid-loving plants, but the neutrality of coffee grounds won't measurably acidify soil. As coffee grounds decompose, they release a small amount of nitrogen fertilizer. Some research indicates that coffee grounds might inhibit damaging rot-type fungus from establishing in soil.
The equivalent of a one-inch layer, accumulated per year, cultivated into the soil surface is a safe, beneficial amount to add to houseplant soil. Extra coffee grounds are great additions to the compost bin, or spread on the surface of gardens and flowerbeds. They improve soil structure, add a little fertilizer, and the scratchy texture of dry coffee grounds can reduce slug damage around plants.
What about that half-cup of leftover cold coffee? Can we dump it on a plant? Yes, research shows liquid coffee can be poured on houseplants in moderation. Besides nitrogen, coffee contains a little phosphorous and potassium. The acidity of liquid coffee would be appreciated by acid-loving plants like azalea. The acidity also helps neutralize the buildup of alkaline salts that accumulate from houseplant watering.
If you have a gardening or lawn care question, email Don Kinzler at ForumGrowingTogether@hotmail.com. All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.