Better to save or get rid of old soil? A little of both

I have a couple of questions about my garden. First, how often should potting soil be changed out of outdoor planters and pots? I’ve been changing out soil every year, but just wondering if I’m wasting my money on soil.

Second, I have some absolutely gorgeous Russian sage in my xeriscape. Unfortunately, each year it sprouts a lot of baby plants where I do not want them. Can I spray them with RoundUp, or will that kill the host plants also? What are my choices for controlling its spread?

— Julie

Here is what I do. In the fall, after the flowers have frozen and died down, I pull up and throw away the bulk of the above ground parts of the plants.

I then dump the soil out of the pot onto a gardener’s ground cloth. I step onto that rootball (since it tends to stay together with all the roots that grew that season), breaking it up. I then “filter” through the soil with my hands, pulling out any hard rootballs, tags and masses of roots.

What I’m left with is a fine, clean potting soil that I then pour back into the pot. I leave the pots this way over the winter. They look a lot better this way by the front door and we often put evergreen boughs and candles in them at Christmastime.

Come spring, when it’s time to plant, I’ll add a bit of fresh potting soil to the pots since I lost some bulk while cleaning them up the fall before.

I’ve done our pots this way for four or five years now and the soil seems to hold up well and grows beautiful flowers for us every year.

As for your Russian sage, you have to be careful here.

There are times when these small plants are seedlings that have germinated from the parent plants. Because they’re not connected to the mother plant, using an herbicide on them would be safe for the plants you want to save.

An alternative to using the glyphosate (RoundUp) would be to apply a pre-emergent herbicide to the area to kill the seeds as they germinate. Apply it early in the spring, when the forsythia (those big shrubs with the bright yellow flowers) are blooming, and then repeat it six to eight weeks later.

However, there are times when these plants are suckers popping up from the base of the mother plant. In this case, using a systemic herbicide such as glyphosate has the potential to greatly harm the parent plants (and the pre-emergent won’t help you). In a case such as this, you have to dig up the suckers and remove them.

To know which one you’re dealing with, do a bit of digging to see what’s going on underground. If it’s a seedling, there should be a small root system arising from that individual plant. If it’s a sucker, there’s usually a thicker underground stem (a rhizome) that’s heading back in the direction of the parent plant.

I would like information on starting and growing sweet potatoes.

— Ann

Sweet potatoes are started differently than regular potatoes.

First of all, they’re planted later than regular potatoes. Sweet potatoes are a warm season crop and they’re usually planted sometime after the first of May.

They like warm weather and toasty soil so don’t try to do them too soon. The second thing about them that’s different is they are planted from little sprouts and not from pieces of the tuber as is a regular potato.

Sweet potatoes love a rich, organic and well-drained soil, so do an extra good job of amending the soil with lots of decomposed organic matter such as Soil Pep and compost.

The plant is a beautiful vine with heart-shaped leaves and it bears pretty round flowers that are a soft yellow-orange. It needs regular watering but don’t keep the soil wet all the time or the tubers will rot. Also, be sure to feed the plant regularly with a good garden type fertilizer.

Finally, be patient with these guys. It takes a long time for the sweet potatoes to mature. You’re usually digging them in October.

Dennis Hill is the nursery manager at Bookcliff Gardens, Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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