Q. I'm working on a "wasteland" that was covered with Devil's Guts in our backyard. I've dug up most of the roots. I don't want to grow anything there. I plan to cover the ground with play-sand. Then sheets of fabric. Then bark mulch. I really want to win this battle with the Devil. Please help.
Dennis Chan, email
A. At least one kind of weed can come up through landscape fabric- especially the more loosely-woven fabrics. Couch grass, which has needle-like root tips, definitely comes through. The only way to prevent this is by removing every scrap of root.
I don't think several sheets of landscape fabric would be any more effective than one against the type of weed that can pierce through. The only layer I've found effective against all weeds is black plastic.
Unfortunately, black plastic has problems too. It gets brittle with age, holds water in low spots and looks ugly unless covered. Bark mulch on black plastic rots unusually fast.
Your proposed solution using landscape fabric is quite workable. Since morning glory shoots (a.k.a. devil's guts) are soft and pliable, I don't think they'll shoot through-but they'll make a mighty effort to escape around the side.
That's why it would be best to check the edges of your sand/fabric/mulch patch frequently so that you can pull any stray shoots.
Sand under the landscape fabric is a good idea. It will even out the ground and make an excellent base- and while you're going to all that work, you might as well make the landscape fabric a double layer.
Three inches of bark mulch should be an adequate topping. But you need to know weeds will blow seed into it-so you won't be entirely free of weeding. A Dutch hoe should keep the mulch stirred up enough that weeds won't set roots down into the fabric.
As sand and gravel mulches age, they also become vulner-able to air-borne weed seeds. Leaves blow onto them in fall, dead needles migrate from conifer trees and in strong winds, soil can drift in. This means any mulch you might choose may need a small amount of weeding at times. But it's far less trouble than coping with a large mass of Devil's Guts.
Q. Are hollyhocks biennial plants? I planted one in early summer. The plant grew tall with lots of big leaves but no flowers. Does my soil contain too much nitrogen?
Heidi Hilmar, email
Hollyhocks are one of those confusing perennials that may flower the first year if seed is sown early. But usually they make vegetative growth the first year and flower in their second year.
Your plant is behaving according to the nature of hollyhocks. Too much nitrogen is unlikely to be a factor. I'm sure you'll get flowers next year.
Older varieties of hollyhocks can get bad rust problems on their leaves. Planting them in a warm, sunny spot can reduce this-but there is also a variety called "Antwerp" that is said to be rust-resistant.
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