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Garden Plot: Now's the time to plant your potted plants

Sunday - 11/17/2013, 9:37am  ET

Flower (Photo by China Photos/Getty Images)
It's that time of year to plant your potted plants (China Photos/Getty Images)

Time to start planting

Mike McGrath, Garden Plot

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Are leaves too acidic to mow into a lawn?

Bob in Fairfax writes: "My lawn is cut at the highest setting the mower will allow (based on your advice) and I mulch the grass clippings back into the lawn (also per your advice,) and the lawn looks great. My question: Are the vast amounts of leaves collecting on my lawn too acidic to also mulch into the grass? (I've heard that they are.) Should I just rake or vac them up and bag them?"

Not if you're going to put those precious leaves out at the curb, Bob. I would support your collecting them if you're going to shred them up for mulch or compost making. But if you're going to otherwise (gasp!) dispose of them, do mow them into the lawn—it's great for your soil life.

Now some leaves are acidic (especially oak leaves), but that's no reason not to use them. Many soils in our area are already naturally acidic, and lawn owners often have to adjust their soil pH to compensate for this. So make good use of your leaves now and have your soil tested in the spring. If the test shows a low pH (below 6.5), add some lime — or even better, ashes from a hardwood stove — to bring it up. I actually prefer wood ash for this chore. It raises soil pH just as well as lime, and people who burn wood over the winter are always thrilled when someone can put their waste to good use.

Keep that rosemary 'Christmas Tree' alive

Thanksgiving is still a ways away, but one of my favorite holiday plants has already begun to appear at garden centers and upscale supermarkets — those beautiful, fragrant, cone-shaped rosemary "Christmas trees."

These plants make great holiday gifts, and even outdoor decorations. Unlike those tropical poinsettias, rosemary is a pretty tough plant that can survive outdoors in a pot on all but the coldest nights. Just not in the pot it rode in on.

That's because the only problem with these plants is that they're pruned to that Christmassy-shape from really big shrubs with really big root systems and are severely rootbound in those little-bitty pots. In fact, there's so little soil in these pots that the "trees" generally brown out and die within a week because there's nothing in there to hold any water. The answer is to repot them.

It's very easy to do. As soon as you get your little tree home, take it out of its pot (the big root ball will slide out easily) and repot it into a container at least twice the size. Use compost or a high-quality bagged potting soil to add the necessary height at the bottom and to fill in around the sides (do NOT use outdoor dirt). Then sit the pot in a sink with some water in the bottom for an hour or so, lift it out, let it drain and then position it in a bright spot that's away from radiators and other sources of heat. (Or even on your front steps -- just bring in inside for the night if temps are going to drop below 30 degrees.)

Check the pot frequently to see if it still feels heavy (well-watered) or light (in need of water) and repeat this "wise watering" regimen whenever it feels light. Your little tree should then make it all the way through the holidays, and maybe even survive to go outside into your garden in the spring.

Fall pruning warning and scale control tips

Phil in Georgetown writes: "I went to prune my dwarf cherry laurel bush and found some kind of pest on it -- little white triangular bumps on some of the branches. Can you help me identify what it is and how to treat it?"

Well first, put down those pruners, Phil. Fall pruning stresses plants and makes them prone to winter injury and weakened plants are more likely to be attacked by unwanted insects like your scale.

Now, you can safely smother these pests with horticultural oil, although scale generally only shows up on these plants when they're being stressed. So if you've been feeding your cherry laurel, stop (it doesn't need it.) If you have any kind of mulch touching the base of the plants, pull it back (and if it's wood or bark mulch, throw it away.) And don't overwater—cherry laurels can't stand wet feet.

Great time to put potted plants in the ground

Ed in Alexandria writes: "Back in August we transferred some hydrangeas to large planters to protect them during a big backyard renovation that was just completed. They did not thrive in the spot they had been in before, but have done much better in the planters in a different location. Should we leave them in the pots over the winter or get them in the ground ASAP?"

You can never depend on potted plants to survive winter outdoors, Ed. A week of frozen nights and they're forever dead.

So yes, plant them in the ground now. And yes, do plant them in this new location, where I presume the sunlight and drainage are better.

Water them deeply and slowly at the base for a few hours after planting, but don't feed them or mulch them with any kind of wood. And wait to prune them until after the new flowers appear next year. That's how you get the best blooming show.

To leaf? Or not to leaf?

Joan in Warrenton writes: "The issue is removing vs. leaving fallen leaves on top of the plants in our beds. I think that leaving unshredded leaves on top of plants over the winter will kill them. Can you clarify this issue?"

My pleasure Joan. Although plants can sometimes survive a light amount of leaf cover in a dry fall and winter, it still isn't a good idea. And a heavy layer of leaves and/or wet weather will turn those whole leaves into a plant-killing tarp that will smother everything underneath.

It's one of the ways that trees reduce competition from other plants — by using dropped leaves to smother their smaller neighbors in the fall. So use a leaf blower set on reverse to suck up and shred those leaves. Then you can put the shredded leaves right back into place on your beds to safely retain soil moisture, keep weeds down and attract earthworms.

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