Gardening columnist Adrian Higgins answered questions recently in an online Washington Post chat. Here is an edited excerpt.
Q: I cleaned out the fireplace to get ready for the winter season. Can I spread wood ash in the yard and/or garden?
A: Yes, a thin layer of wood ashes will add potassium and other elements to the soil. Although some areas already have plenty of potassium in their soils so a bit of research on this is advised. I like to dig mine in the fall, along with shredded leaves, so the soil is ready to go for spring planting. According to some experts, you shouldn’t add ash to the compost pile because its high pH inhibits microbial life. If you have a wood fire or stove, I would highly recommend buying a large metal bucket so you can store ashes that might still have embers, which can persist for days.
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Q: We put in a new raised bed last year in our vegetable garden and filled the bed with soil. We are building additional beds this fall. Do you recommend filling with soil, or should we consider rocks and sand in the bottom foot or so of the bed?
A: Definitely don’t add rocks for drainage; you’ll be digging them up for years to come. I am a big fan of adding sand to vegetable beds, not as a layer but mixed in with compost and soil when I create the beds. That would be my recommendation. Use a lot of it, maybe one part of each.
Q: We’d like to get rid of invasive English ivy, some Japanese honeysuckle, vinca and poison ivy. Because we are both highly allergic to poison ivy, we will need to hire out the job. What methods are most effective?
A: Poison ivy is easy to spot in the fall because it turns a beautiful scarlet color. All these vines can be cut to the ground and the cut stem treated with herbicide. If the ivy is on a fence or tree, it’s best to let the severed top growth die off over the winter before ripping it down.
Q: When we had the front of our house professionally landscaped, they planted one hydrangea plant. I remember telling the designer I wanted small and low maintenance. It was really pretty the first couple years but then slowly grew and grew and grew. It’s at the point where it’s completely taken over the space and doesn’t produce any blooms. I’ve chopped it way down to ground level for the winter, but I really want to relocate it to the back yard where it can go wild. At what point can I move it? Also, the spot I want to move it to is shadier than the current spot.
A: This is my annual spiel about hydrangeas. If you cut them back hard now or in the winter or spring, they won’t bloom next June. If new growth is zapped by a late frost in April, the flowering will also be nonexistent or diminished for the year. You can’t treat a hortensia hydrangea like a perennial and chop it back hard; if it is twiggy and congested, you should prune some of the older canes. I would wait until the summer to do this because these twigs offer some extra hardiness in the winter and spring. You can move your hydrangea, but add some organic matter to its new site, water it well, add a little mulch, and be patient. It will take a couple of years to return to blooming size, unless it is one of the newer reblooming types. That’s doesn’t sound the case, since it hasn’t flowered for you. This lack of blooming is probably due to improper pruning.
Q: I have three unappealing arborvitae. I want to replace them, preferably with something that provides good bird habitat without growing too wide. Have any good options for me?
A: I might try something more shrubby, which will give birds a place to roost and get away from predators. Is Burford holly too trite? You could try yaupon or American hollies or larger forms of false cypress.