Another April freeze; tree roots vs. pavement; rhubarb and zoysia

Meet Mike on Saturday and Sunday, April 16 and 17, at The Calvert (County) Home Show in Prince Frederick, Maryland. Details here.

Time for another April freeze!

It’s been said that “April is the cruelest month,” and area gardeners will be happy to tell you why that’s been especially true this year — although not in language that I can repeat on the air or on the Internet.

Some forecasts for the weather Saturday night into Sunday morning is for bone-chilling cold, even in the heat sink of the city, where temps are normally much more mild.

It’ll be even colder in the outskirts — with a chance of snow! Oy!

If you have any houseplants or tender plants like baby tomatoes outside, get them inside now. Don’t worry about spring bulbs, pansies, lettuce, spinach or other plants that love cold weather. Trees and shrubs that are in full flower could see some of their blossoms damaged (my hydrangeas got hammered when this happened last week), but the plants themselves should be fine.

If you have any easy-to-reach shrubs in full flower that you’d like to try to protect, you can cover them with a floating row cover fabric blanket such as Reemay (the biggest brand name) or sheer curtains — but no blankets or heavy fabrics that could crush the plants.

Tree roots 1, Pavement 0

Bill in Springfield writes: “I have a large maple tree in my front yard and one of the roots has broken a couple of walkway stones. To repair the walk, the root will have to be severed. Should I be concerned about the health of the tree afterward?”

Above-ground roots are very common with maples, Bill — they’re actually a good sign that the tree is healthy. My first choice would always be to consider rerouting the walkway. If that’s not an option, you should be able to remove one root without harming the tree.

Make a clean cut, seal the pruning cut with white latex paint and refill the area with the same soil you removed after the paint has been allowed to dry. Don’t fertilize the tree afterward and keep any mulch a good foot away from the trunk.


Caryl in Warrenton writes: “Can I grow rhubarb here in Northern Virginia? Or is it a lost cause because it gets so hot in summer?  If I can grow it, which varieties might work best?”

Ah yes, rhubarb — the amazing garden oddity: A member of the buckwheat family, it’s the only vegetable we use as a fruit and the only garden crop whose leaves are toxic but whose stalks are safe to eat.

Although rhubarb does grow best in the far north, it should do well in Northern Virginia, especially if you can plant it where it will get some afternoon shade in the summer and where you can keep it watered during dry spells. The varieties “cherry” and “cherry red” are the best choices for regions with hot summers.

Rhubarb crowns can be planted in the spring or fall. Pick a spot that drains well and dig a deep hole — the size of a bushel basket — and fill it back up halfway with well-aged manure or high-quality compost (rhubarb likes growing in very rich soil; half aged manure and half compost would be ideal). Rhubarb also requires excellent drainage, so mix in some sand or pearlite (a natural mined volcanic material available in any garden center) as you go — especially if your soil is heavy.

Place the “crown” (the root-like thing you plant to grow rhubarb) on top of the rich, loose mix and then fill the rest of the hole up with more of the same. Then mulch the area well with straw or pine straw to keep the soil cool. (Not wood mulch or anything else that’s “heavy”; you want a light, loose mulch.)

Keep that area well-watered during dry times, especially as the plant is getting established. Make sure it gets an inch of water every week — either from rainfall or from you. (A hose set to drip slowly for an hour is the best way to really saturate the soil). Don’t harvest any stalks the first year; just admire them. You can harvest a few the second year (snap them off after the stalks have turned fully red; don’t cut them with a knife). But don’t go nuts; the plant is still getting established.

After that, you’ll be able to make your own rhubarb pies for many years to come. Just remember to remove any trace of the toxic leaves and use only the fully red stalks.

Zoysia is a grass, not a weed *

Jasmine in Chantilly writes: “Will the new nontoxic, iron-based herbicides like ‘Iron X’ kill zoysia grass? I ask because I’ve heard that zoysia is considered a weed.”

Ha! No, they will not, Jasmine — iron-based herbicides kill a wide variety of weeds but do not affect any grasses, which makes them perfect to use on lawns.

And although it does spread laterally and can get into flower beds if they’re not protected by deep edging, zoysia is a lawn grass — as are Bermuda and bluegrass, which both have the same spreading habit (which means they can creep into unwanted areas if edging is not in place, but also that they can fill in their own bare spots).

So if you want to spray one of the new iron-based herbicides on weeds that are growing in a zoysia grass lawn, go right ahead. But it won’t kill zoysia grass that has invaded nearby areas.

*Unless it’s where you don’t want it, of course.

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