Episode 37 – Why the right soil matters, hardening off plants, and avoiding oak wilt

Welcome! If you’re here wondering why our radio show on WOOD Radio in Grand Rapids isn’t on at it’s usual time of 9am Saturdays, that’s because the Riverbank Run is being broadcast instead. Tune in at 5pm ET today to hear this week’s show, or catch us now on YouTube or at your favorite podcast platform. 

Ground Breaking Banter - Rick

Mid May? It’s “Grow” time! 

We start out this episode with random thoughts to the early stages of a long growing season. It’s a marathon, folks! Rick shares one of his favorite quotes from Charles M. Schulz, creator of Peanuts, Charlie Brown, and Snoopy: “Running is good for the ground. It makes it feel needed.”

There are so many simple things you can do to improve your odds in the garden from the start. For example, when you put those young fledgling plants in the ground remember to BYOB. No, not bring your own beer – “build your own basin.” When you plant, use the soil to sculpt a basin around the plant to hold water and nutrients when initially establishing the plants. We’ve talked about deep-planting tomato plants, this is another helpful step in the initial stages of development so water and nutrients get to the roots where needed instead of running away.

Soil is not a single entity, it’s a mix of several things. I call the existing soil the “parent soil.” When you amend with organic matter, like compost or composted manure, mix it in completely with the existing parent soil for best results. In Europe (namely UK), they call what we call bags of potting soil “compost.” I think their terminology is similar to us buying a chocolate bar at the store. We call it a chocolate bar, not what it really is: “sugar and fat with food colorings and some cocoa in it.” It does bring up the point regardless of what you call it, use good quality potting mixes in your containers.

Take me to your weeder! Important to keep up with the weeds (they can compete for needed moisture, sunlight and nutrients. Stacey and Rick agree that having an understanding of the difference between annual and perennial weeds will make a difference for you in effective weed management. Rick says auf-“weed”-ersehen to weeds until we see you again!

You’ll see a lot of “gardening hacks” on the internet. Even from Investing.com! While some are kind of cute, like flattening spoons to make plant markers, others are either horticulturally questionable or just plain wrong. So as you browse the internet, or social media, or Pinterest (one of the worst offenders!), take the ideas you see with a grain of salt unless they come from a reputable source.

Consider an investment in fertilizer “prills” slow release (4 month) process of osmosis with nutrients releasing through a semipermeable membrane. (You will often see them in a pot that you buy at a garden center). No, they are not “insect eggs.” It’s a quality fertilizer and the prills, also called pellets, are coated with a type of resin. The semi-permeable coating, often made from linseed oil, allows some water to get through and start to dissolve the fertilizer inside, the fertilizer works by releasing fertilizer through the resin coating by the process of osmosis. The release rate depends on temperature and coating thickness.

Why: Since we’re talking about soil, I wanted to pick a plant where having the right soil really matters, and explain why. So I picked a rhododendron, which are notorious for their demand for acidic soils, and the one I picked is our best-selling classic rhododendron, Dandy Man Purple. Just why do rhododendrons and their relatives – which include azaleas, blueberry, pieris, mountain laurel, cranberry, and wintergreen – need acidic soil? It’s not because of their roots’ physical tolerance to the conditions. It’s because the pH level of the soil controls how available various essential nutrients are to the plant to take up, as you can see in this chart. The sweet spot, where all nutrients are available abundantly, is in the 6-6.5 range, and below that, you see huge availability of iron, which rhododendrons love, as nitrogen and potassium. So when we talk about a plant’s pH preference, we’re not necessarily saying it literally grows best in soil that’s acidic or alkaline, rather, that its nutrient needs are best met by the conditions created in an acidic or alkaline soil.

Also, as you can see, Dandy Man Purple rhododendron is just plain beautiful! And it will be blooming very soon for us here in West Michigan; if you live in a warmer climate, rhododendrons like this one likely bloomed a few weeks ago. 

Who: Dandy Man Purple rhododendron came to join the line of Proven Winners ColorChoice Shrubs from the estate of the late Joe Parks, who was a former president of the Massachusetts chapter of the American Rhododendron Society and a founding member of the Maine Coastal Botanical Garden. As you can read in his obituary, he was a Renaissance man with a huge range of interests, and a trip to the Arctic at the age of 90 to study plants among his achievements. He developed the plant that would become Dandy Man Purple to fill a need for exceptionally showy rhododendrons for cold climates, and indeed, Dandy Man Purple is hardy all the way down to USDA zone 4 and heat tolerant through USDA zone 8. 

How to grow: Rhododendrons are beloved for their shade tolerance, a trait that has placed them in front yard landscapes across the country, and they were prevalently planted this way in the Detroit suburbs where I grew up. They can take full sun, provided you have moist enough soil, but do best in part sun conditions where they get 4-6 hours of sun per day. They can grow in deeper shade, however, their flowering will be compromised and they will take on a more sparse and open habit. 

We’ve already covered how rhododendrons need acidic soil; they also need a good 2-3″ layer of shredded bark mulch over the roots. This serves two crucial purposes: it keeps the shallow roots cool and moist in summer and conserves soil moisture and insulates roots in winter. Rhododendrons grown without mulch, or those grown with a rock mulch, will not be as happy and vigorous as those who enjoy a good organic mulch.

If you find that your rhododendron frequently has yellow foliage and you are fertilizing it in response, this usually indicates that the soil pH is too high (neutral-alkaline), which is tying up iron and preventing the plant from taking it up. Fertilizer and/or iron supplements will be fine as a temporary fix, but a more sustainable approach is to get a soil test and fix the pH according to its recommendations based on the results. 

Generally speaking, you should avoid pruning rhododendrons unless it is to selectively remove branches to attain the habit and spread you desire. They should not be trimmed or cut back at all. This is one of those plants that’s really best left to do its thing so you can enjoy it!

If you’d like to add Dandy Man Purple rhododendron – or any of the 320+ Proven Winners ColorChoice Shrubs – to your garden or landscape, you’ll find a list of local retailers here

Gardening Mail Bag - Stacey

Late spring is a great time to plant them, but yes, they absolutely should be hardened off first. Hardening off is the process of transitioning seedlings from the protected environment of the indoors to the much harsher outdoors, where the sun is brighter and winds are stronger. All it entails is putting the plants outside in a shaded spot for a few hours for a couple of days. Then, a little more sun for a few more days, before moving them into full sun for a few hours each day before letting them fend for themselves. 

No! Oak wilt is a catastrophic disease of oaks that is spread not just through pruning but through open wounds in oak trees when the fungal spores are in the air. Infection is fatal and always kills trees, though fortunately not all types of oak are equally susceptible – white oaks are more resistant than black and red types. Because pruning and chipping oaks can spread the disease, one of the primary management strategies for now is to avoid pruning oaks during dangerous times. In areas where oak wilt is present – which includes most of  the Midwest, as well as parts of South Carolina and Texas, oaks should not be pruned spring through early summer. The exact months will vary because of the variations in climates, but here in Michigan, the no-prune time is April through July; some say early August. But play it safe and only prune, or even cut back, oaks when they are dormant in fall and winter.

Cutting back or tip-pruning ninebarks will ruin their naturally elegant appearance, and we firmly do not recommend it. It will cause the plant to develop a witches broom appearance, with burst of foliage sticking upright, and it could also remove flowers if done at the wrong time. Instead, we recommend selectively removing entire branches, but even this isn’t strictly necessary. Ninebarks, like today’s Plant on Trial, Dandy Man Purple rhododendron, are best left unpruned to develop their own natural habit.

Do you have a question for us? We’re happy to help! E-mail us or use the contact tab above.

Branching News - Rick

  • There are those who are nostalgic about gardening but, in their words, “have no time.”  For them, a new business in the Philadelphia area will install and maintain a vegetable garden for you, but at a cost: an average garden project, including two 4-by-8-foot beds, starts at $5,000 for a one-time installation fee, plus roughly $1,000-$2,000 for planting and full-service maintenance from March through November.
  • That story inspired Rick’s Limb-a-Rick for this week:

My raised vegetable garden I commence,

In its construction I will spare no expense,

The components cost me lots of dough,

I calculated each backyard tomato,

cost me 52 dollars and 39 cents!

  • Thank you for the thousands and thousands of Gardening Simplified Show podcast downloads! What do you do while you listen? A recent study tells us what people are doing while listening to a podcast:

    Doing household chores—30%
    Driving around—30%
    Unwinding after a long day—24%
    Taking a walk—24%
    Eating a meal/lunchbreak—18%
    Getting ready for the day—17%
    Working out—17%
  • Get 101 creative names for your plant, or according to them, your “Sweet, Precious, Angelic Plant Babies.” 
  • In 2002, residents led a public campaign to save a large white ash tree when the city announced plans to remove it for construction of a curb ramp. The neighbors prevailed, but the victory was temporary. In 2015, the city finally cut down the tree as a safety precaution because of decay from emerald ash borers. Akron artist Michael Marras, who had long admired the tree, turned the stump into artwork in September 2016 when he secretly installed a sword. Neighbors were mystified one day to wake up and see Excalibur. According to Arthurian legend, a magical sword was embedded in a stone and engraved with the inscription: “Whoso pulleth out this sword of this stone and anvil is rightwise king born of all England.” Arthur, then a boy, removed Excalibur with ease when no one else could. Well, this time, the sword had to be removed by arborists as the rotting stump had to be removed.
  • Remember the story we did on neighborhoods complaining about the noise of pickleball courts popping up all over the place? The solution may lie in abandoned box stores!
  • An extended gardening season here in the north this fall and winter? At least Rick is hoping so! His good friend El Nino may be showing up soon. Speak of El Niño, there’s a new shrub from Proven Winners ColorChoice with that name, and it’s one of Stacey’s favorites: El Niño ×Chitalpa. Also known as desert orchid, this unique hybrid of two native species, Catalpa and Chilopsis, has orchid-like flowers that emanate the most incredible melon-vanilla scent that you just have to smell to believe. This is a truly special new plant, perfect for people who garden in full sun and dry soil and love fragrant plants (like Stacey).


Pink rose of Sharon flowers bloom on a plant with variegated foliage.

Episode 92 – Weeding by Example

Ah, weeds – maybe the #1 thing that discourages people from gardening. But weeds are interesting and become a lot easier to manage when you apply some basic IPM principles. Featured shrub: Sugar Tip rose of Sharon.

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