How to get rid of that pesky rose fungus

DEAR JESSICA: I have a rose leaf problem. I noticed this in the fall when I was cleaning up the yard. What do you think has caused this? Please let me know what I can do to treat it.

— Mari James,

Sea Cliff

DEAR MARI: Your roses have contracted one of the most common — and most destructive — rose diseases: Black spot. The pathogen is caused by the fungus Diplocarpon rosae. Left unchecked, blooms are diminished and plants are severely weakened, making them more susceptible to winter injury and other diseases and pests.

Prune away all infected branches and dispose of them properly. Be sure to rake well and discard all leaves and debris in sealed trash bags; allowing them to remain on the soil will lead to reinfection. Remove infected leaves, but not if the weather is humid, as moisture will facilitate the spread of spores when plants are disturbed.

There are many fungicides indicated for the prevention and treatment of black spot. Among the most environmentally friendly are Neem oil (applied every 7-14 days) and copper fungicides. Apply after cleaning plants when you first notice symptoms, and take care to follow package directions carefully.

In addition, spraying a solution of one tablespoon each of baking soda and ultrafine horticultural oil diluted in a gallon of water is an effective preventive for black spot and other fungal and mildew diseases. Don’t be tempted to use more baking soda than recommended, however, because its salt content can injure plants if overused.

Planting onions or tomatoes near roses also will help discourage black spot fungal infections. Good cultural practices can go a long way, too: Space plants sufficiently to allow light and air circulation to reach the inner branches. Water deeply only once a week (less during rainy periods) using a soaker hose, which directs water straight to roots and keeps foliage dry (overhead sprinklers and other methods that wet leaves encourage the growth of fungal diseases such as powdery mildew, in addition to black spot).

DEAR JESSICA: When I brought my houseplants in September or October, I thought I was supposed to repot them, which I did. You recently wrote that repotting should be done when you put them out. Should I or should I not repot this spring? I have followed your suggestions for getting poinsettias to rebloom. Can you advise how to get amaryllis to rebloom?

— Kenneth Geller,

via email

DEAR KEN: If you repotted your houseplants last fall, then you shouldn’t repot again in spring. The point is to give roots room to expand before the growing season begins — if they are outgrowing their current pots. It’s important, however, only to move up to the next size pot — never more than a 2-inch increase in pot size at a time.

Amaryllis are easy rebloomers — to be honest, I’ve ignored mine completely over the winter, forgot about them in a corner of the room, and had beautiful blooms the following December.

Plants require a resting period for repeat blooms, so, if you’re going to keep the plant active after blooming, place it in a sunny spot and water only slightly over the winter, place it outdoors (gradually acclimate) in spring and resume regular water and monthly fertilizer. Then let it “rest” for 8-12 weeks during September/October/November by placing it in the dark and withholding water. After the resting period, cut away dried plant parts and set the plant by a sunny window. A flower stalk will shoot up shortly (sometimes overnight).

Good luck!

DEAR JESSICA: You recently advised readers not to apply mulch until the middle of May. My question is the reverse: When should I remove leaves from underneath rose and hydrangea bushes? I put lots of leaves under them for winter warmth.

— Jeffrey Stark,

via email

DEAR JEFFREY: Actually, you put lots of leaves under your plants to keep them cold. Winter mulch reduces winter freeze-thaw cycles by trapping cold in the soil, keeping shallow roots (and grafts) in the ground, where they belong, and ensuring plants remain dormant. Removing winter mulch too soon may encourage early growth, which could be damaged by a late frost (or freeze), so you should wait until the danger of frost has passed, around mid-April or at the first sign of new growth.

DEAR JESSICA: Six years ago, we built three planters for our deck. Each is 6 feet wide by 2 feet deep and 2 feet high. Together these planters hold 72 cubic feet. To reduce the amount of potting soil we’d need, we decided to fill the planters halfway with packing peanuts, then used half the amount of potting soil. With the planters set, we watered the soil and planned to plant the next day. Much to our surprise, the soil sank down to only 1 foot deep. We did not realize the peanuts we used were biodegradable and simply melted away. So an FYI to your readers: Make sure the packing peanuts you use are not biodegradable.

— Bruce and Leona Keeler,

Malverne

DEAR BRUCE AND LEONA: That’s a wonderful observation. I always fill the bottom of too-deep planters with packing peanuts or gallon milk jugs before adding potting mix. Crushed soda cans or capped plastic bottles also can be used. It’s a great way to recycle those items and save money on soil. It also lightens large pots that would otherwise be too heavy to move.

For the past 20 years, however, many packing peanuts have been made from cornstarch or sorghum instead of the traditional polystyrene, or Styrofoam. This is great for the environment, as they are biodegradable, and nontoxic if accidentally ingested by children or pets. They also can be disposed of simply by dissolving in water, or composted. It’s that last part that worked against you.

I wouldn’t recommend purchasing polystyrene peanuts for the purpose of packing a planter, but it’s a wonderful way to repurpose them, should you already have some. I sometimes place starch peanuts in sealed plastic bags and add those to the bottoms of pots I replant every season, but I wouldn’t do that in raised beds or in larger applications because of the threat of leakage. Thanks for sharing your experience.