Garden Plot: Keep your roses growing with the right mulch

Meet Mike in Fredericksburg this weekend!

Mike will appear on Saturday, March 12 and Sunday, March 13 at the Spring Home Show at the Fredericksburg Expo Center. He’ll give talks on Saturday at 11 a.m., 3 p.m. and 4:30 p.m. and Sunday at 11:30 a.m. and 1 p.m.

Claude Loves Roses & Roses Love Compost

Claude in D.C. writes: “Every year I plant some new Heritage English rose bushes for my wife on our anniversary. After five years, we have quite a rose hedge going. They start out lush and full of blooms in the spring, but as the summer heat stresses them, they get leggy and blackspot tends to set in. I’ve heard your advice about using compost instead of wood mulch around roses. Do I have to remove the old mulch before spreading the compost?”

Absolutely, Claude! That old mulch is full of blackspot spores from last season, and should be removed ASAP. Then prune the roses back, removing any portions of canes that show signs of disease, remove the prunings and spread two inches of compost as the new mulch.

Claude in D.C. gets the message and is replacing the wood mulch around his wife’s black-spotted rose bushes with compost (specifically Maryland’s great LeafGro compost, he notes).

And that’s a change “allayose” should make! Because while wood mulch is not good for any plantings, it’s especially bad news under disease-prone plants such as lilacs and roses.

The reason is simple. Decomposing wood is the favorite breeding ground for many fungal organisms — including the house and car-staining artillery fungus, the X-rated stinkhorn fungus (that looks like someone decorated your landscape with sex toys) and a battery of diseases such as blackspot.

Compost mulch doesn’t breed these baddies. In fact, compost suppresses them.

Turn Old Wood Mulch into Future Compost

Claude in D.C. continues: “But what do I do with the old (wood) mulch? Can I dump it in my compost bin or send it to the garbage dump?”

Don’t contaminate your existing pile with that old wood, but do compost it, Claude. Although wood mulches breed disease and nuisance molds for their first couple of years, they eventually break down into compost.

So, make a new dedicated pile of that old mulch and mix in lots of spent coffee grounds as you go. Most coffee shops will be glad to give you big batches. The nitrogen in the coffee grounds will move the process along quickly, and the compost will be safe to use when you can no longer see any trace of wood in there.

Your Sure-Fire Plan for Great-Looking Roses

  • Remove last year’s mulch, no matter what it was.
  • Prune away any dead, damaged or diseased canes and open up crowded areas to improve the airflow.
  • Discard that old mulch and your prunings. Don’t leave them near the plants.
  • Apply two inches of high quality compost as the new mulch. Do not subject your poor roses to wood, bark, root, licorice or other disease-promoting mulches.
  • Do not feed or otherwise treat the plants. The compost will take care of everything.
  • Remove faded flowers promptly and prune all of the canes back after the first flowering to encourage new blooms and to keep the bushes nice and compact.
  • But do not prune your roses — or anything else — after Aug. 1.

Time to Plan for Corn Gluten to Battle Your Crabgrass

Joe in Derwood writes: “I’m getting ready to spread my corn gluten meal — can you supply the website links for the local soil temperature?”

Yes, Joe. Below, you (and everyone else) will find the link to the USDA soil probe at Powder Mill, Maryland (the only such probe in the D.C. area) and a link to the buoys that report the live time temperature of the water in and around the Chesapeake Bay, as that water temp closely mimics the temperature of the soil as measured four inches down (which is the depth of measurement you want).

In a nutshell: Crabgrass seed germinates at a soil temperature of 55 degrees F (as measured four inches down). Corn gluten meal is a natural fertilizer that contains the perfect amount of non-chemical slow-release nitrogen for lawn feeding and also naturally prevents the germination of seeds — in essence, a natural form of weed and feed.

Based on the current soil and water temps, the long-range weather forecast for our area, and the timing of previous seasons, I predict that the soil will begin to reach that temperature in about two weeks. The natural pre-emergent herbicidal activity of corn gluten meal lasts six weeks, so you’re pretty much good to go anytime now.

Ideally, apply it when a rainy spell (or a thorough watering by you) will be followed by dry weather, which increases its effectiveness.

How to use the USDA soil probe at Powder Mill infomation: Scroll over to the right at the top of the page to column  No. 11, the soil temp as recorded four inches down. Scroll down to the bottom to find the most recent date. (By the way, this is actually easier than it used to be—last year the readings were in Centigrade!)

Water temps in Chesapeake Bay.

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