167. Is Gravel Gardening Right For You?

We recently spoke with Andrew Bunting of the Pennsylvania Horticultural Society about garden resolutions, and the Philadelphia Flower Show, which will be held this coming June. Go back to Episode 159 of the Garden Basics podcast to find out more about those topics. 
We also talked about the interest in gravel gardening back east and in the midwest. If you are a subscriber to the Garden Basics “Beyond Basics” newsletter, you heard about gravel gardening back in the Dec. 31st, 2021 online newsletter. 
But for the thousands of you who may not have listened to that discussion in the newsletter podcast, we have it for you here, on the Garden Basics podcast, today.
Along with that, Debbie Flower and I will discuss if gravel gardening is really a good idea for those of us in warmer to downright hot climates. 
Plus, does fertilizing cool season annuals - flowers and vegetables - in the winter, really work? As always, the answer is: "It depends."

We’re podcasting from Barking Dog Studios here in the beautiful Abutilon Jungle in Suburban Purgatory, it’s the Garden Basics with Farmer Fred podcast, brought to you today by Smart Pots. 

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Pictured:
The Gravel Garden at Olbrich Botanical Gardens in Wisconsin 

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A Primer on the Gravel Gardens at Olbrich Botanical Gardens in Wisconsin
https://blogs.extension.wisc.edu/flowers/lectures/meadows-and-gravel-gardens/

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Chapters

• 1:51 Is Gravel Gardening Right for You?
• 20:18 Smart Pots!
• 21:20 Garden Basics Newsletter Info
• 22:33 Quick Tip: Cool Season Fertilization

Transcript

Garden Basics with Farmer Fred, Episode 167. TRANSCRIPT.

“Gravel Gardening”, “Fertilizing cool season annuals” Feb. 11, 2022

Farmer Fred  0:00  

Garden Basics with Farmer Fred is brought to you by Smart Pots, the original lightweight, long lasting fabric plant container. it's made in the USA. Visit SmartPots.com slash Fred for more information and a special discount, that's SmartPots.com/Fred. Welcome to the Garden Basics with Farmer Fred podcast. If you're just a beginning gardener or you want good gardening information, you've come to the right spot. 

Farmer Fred  0:33  

We recently spoke with Andrew Bunting of the Pennsylvania Horticultural Society about garden resolutions, and the Philadelphia Flower Show, which will be held this coming June. Go back to Episode 159 of the Garden Basics podcast to find out more about those topics. We also talked about the interest in gravel gardening back east and in the midwest. If you are a subscriber to the Garden Basics “Beyond Basics” newsletter, you heard about gravel gardening back in the Dec. 31st, 2021 online newsletter. But for the thousands of you who may not have listened to that discussion in the newsletter podcast, we have it for you here, on the Garden Basics podcast, today. Along with that, Debbie Flower and I will discuss if gravel gardening is really a good idea for those of us in warmer to downright hot climates. And by the way, don’t confuse gravel gardening with rock gardening. It’s very different.  We’re podcasting from Barking Dog Studios here in the beautiful Abutilon Jungle in Suburban Purgatory, it’s the Garden Basics with Farmer Fred podcast, brought to you today by Smart Pots.  And we will do it all in under 30 minutes. Let’s go!

Farmer Fred  1:54  

We are talking with Andrew Bunting. He is the vice president of public gardens and landscapes at the Pennsylvania Horticultural Society, an internationally recognized organization that was founded a long, long time ago. It's also the producer of the world famous Philadelphia Flower Show. Andrew, thanks for joining us here on the Garden Basics podcast. We touched a little bit about reducing the need to water and, of course, waterwise gardening, or the unfortunate term, xeriscaping, is popular here in California or actually,  it's downright the law. Do you find that there is an interest back there that despite all the summer rain you get, that people want to try waterwise gardening?

Andrew Bunting  2:53  

Yeah, we don't have the same drought situations that a large part of California has. But we do have periods of drought, you know, we might have, you know, a couple months where we get hardly any water whatsoever. So I think for those who want to just reduce water in general, that type of gardening might be appealing, I think out here, it's actually more of a an aesthetic. I love the kind of arid or xeriscape gardens you see in Santa Barbara and Southern California. So that type of aesthetic is one that you often don't see around here. So that's what's starting to gain popularity, and I've seen that actually, across, I would say, the eastern part of the United States. And often where I look for trends is, what are Botanical Gardens and Arboretums doing? They're often some of the trend setting institutions. There's some really good examples of gravel gardens. These are gardens that either just plant into the native soil and up-dress with gravel. Or ,like in my house, I actually excavated out about six inches of soil and put in gravel and kind of grow plants right right into the gravel, and the plants grow through the gravel into the soil below. One of the best gravel gardens, I think, in the entire United States is in a botanical garden called Olbrich Botanic Gardens in Madison, Wisconsin. They have multiple gravel gardens. They show  the public different ways in which they can use gravel aesthetically, as well as kind of the myriad of plants that you might grow in a gravel garden in this part of the country. There's some good public gardens like Scott Arboretum at Swarthmore College. It uses gravel in multiple locations. A famous garden in the suburbs of Philadelphia, Chanticleer, has a fairly extensive gravel garden. I would say here it's almost more of a style of gardening that's gaining in popularity because it also affords you the opportunity to maybe grow types of plants that perhaps you would see more in California, but we don't see that much here. Things like Yuccas, hardy cactus, other succulent plants. A lot of the succulent plants in our native garden soils that get a lot of water in the summer and humidity actually don't do that well, so they really need a sharper drainage. So gravel gardening affords us that type of habitat so that you can grow those plants more successfully.

Farmer Fred  6:02  

Yeah, you would almost need at least six inches of gravel, if not more, just to keep the root zone above the area where the water may puddle below the gravel.

Andrew Bunting  6:12  

Yeah, that's right. It obviously can be, upfront, a greater expense than kind of traditional gardening. But , over time, you really cut down on the water because of the type of plants that you're growing. What I've found with growing plants in pure gravel is once they've grown through and into the soil below that top of four to five inches of gravel is so inhospitable that you hardly get any, any weed seeding into that top layer of gravel. 

Farmer Fred  6:50  

Oh, give it time.

Andrew Bunting  6:51  

Yeah, maybe  if somebody can figure out how to have a truly weed free garden that that would be a major trend.

Farmer Fred  7:03  

Not gonna happen. But what are some of the popular succulents there that can overwinter in those gardens back there?

Andrew Bunting  7:10  

Any of a number  of succlents. Most sedums, hens and chicks, sempervivums, quite a bit of cactus. They're actually hardy here. Not like you're Mexican type cactus, but, you know, a lot of cactus that are native in higher elevation parts of the US like in Colorado, Idaho, Wyoming. Those are hardy here. A few cultivars and species of yuccas, but it's not everything. Not everything that goes into gravel garden has to be a succulent. Once you establish things like some of the different species of Rudbeckia, or actually a lot of the prairie plants, a lot of the grasses and coneflowers and things like that. Because a lot of them have long taproots to kind of survive in Prairie type situations with a multitude of hostile conditions. Once those established they actually do quite well. In my grandma's garden home I have a plant called the Threadleaf Blue Star Amsonia hubrichtii. That that does quite well. All  the false Indigos, they have a fairly significant taproot and also do quite well.

Farmer Fred  8:38  

What about the prickly pears?

Andrew Bunting  8:42  

Oh yeah, prickly pear for sure. Yep. There's different species of prickly pear, but there's actually one that's native to the East Coast. And that does well.

Farmer Fred  8:53  

Okay, that's Opuntia for those of you at home keeping score, and out here that's a weed.

Andrew Bunting  8:59  

Our cactus don't get to be the stature like you see in California, they tend to be either ground covering types, or maybe just get a foot or two tall. But not like what you have on the west coast, where they can be tree-like.

Farmer Fred  9:17  

Andrew Bunting is with the  Pennsylvania Horticultural Society. He is the vice president of public gardens and landscapes. And again, more information online at PHS online.org. Andrew, thanks for helping us get off to 2022 to a good gardening start.

Andrew Bunting  9:36  

You're welcome. Thanks for having me.

Farmer Fred  9:40  

Well, well, well, gravel gardening. Does that apply to people in USDA zone nine and people in the southwest? Because gravel gardening is not rock gardening. That's an interesting garden fad going on back east and Midwest. But how applicable is that to the warmer areas? Debbie Flower is here, our favorite retired college horticultural professor, and Debbie, based on what we just heard, that's an interesting idea that they have going back there. To be able to grow drought tolerant plants in four to five inches of small rock. And they kind of get churlish when you call it rock. They want to call it, garden pebbles or pea rock or something like that.

Debbie Flower  10:25  

Yes, well, they certainly have some specifications for the rock to be used. They don't want it to be limestone, because that will break down over time. And it should all be sized the same size. So it's not just going to a quarry and digging up a bunch of rock and throwing it in your truck and throwing it over the garden. Its sized. So everything is, from what I've been reading and hearing, between a quarter or half inch in size. And with smooth sides. So it's a very specific type of rock. And it could be very expensive, especially to get started. 

Farmer Fred  11:01  

Yeah, four to five inches is quite a bit, not to mention fun to move. 

Debbie Flower  11:05  

Yeah, I have to say that when I have done house-hunting in the past, I shy away from homes that have gravel on part  or all of the landscape because I know that I need to garden and I need to plant things and dig them up and move them and all that fun stuff. And with gravel as the mulch, that makes it more difficult.

Farmer Fred  11:25  

When you're growing in that environment here in California or in the southwest, what are the precautions that you have to take if indeed you do have a rock garden? Heat, I would think, would be a problem.

Debbie Flower  11:40  

There are some plants that prefer a mulch of rock or gravel. But four to five inches is not what what I would consider a mulch for those plants. The goal of gardening for me in a hot dry climate is to create shade and cooler places in the garden in the summertime. And gravel will not allow that because gravel reflects heat and light, especially depending on the color.

Farmer Fred  12:07  

And for really really hot climates like you would find in the Imperial Valley of California or parts of Arizona, New Mexico, even parts of Colorado, I would think that there's even more precautions.

Debbie Flower  12:20  

My husband is from Tucson, Arizona and Tucson has been very aggressive about reducing use of landscape water. What most landscapes have, and in some places you're required to by your CC&R's, is gravel as a mulch. It is not four to five inches deep, it's just an inch or two. And it is not sized like they're talking about in the more formal gravel gardens in the Midwest and East. It is just mined. The landscape mining company delivers it, and either you spread it or their people spread it as a mulch and those tend not to be white, they're not really colors that do lots of reflection. They are more of the tans and grays, which will do less reflection and then the result of using that gravel as a mulch is that you don't have grass and you don't have plants that survive in extremely high heat, which of course you're going to experience in the desert but can be ameliorated with somewhat with an organic mulch that will hold more moisture in the soil. So the landscaping, then, is very Southwestern, which is lots of cactus and trees that are native to the southwest.

Farmer Fred  13:33  

In that segment that we heard with Andrew Bunting, he talked about the gravel gardens in Madison, Wisconsin. He said it's one of the premier locations and he mentioned the Olbrich Botanical Gardens. And if you go online, and we'll have a link to it in the podcast notes. You can see what they've done there as far as putting in a pebble garden. The Olbrich Garden is in Wisconsin, which means they get summer rain. 

Debbie Flower  14:03  

They get summer rains, something we don't get , they get humidity, they're near Great Lakes. Yes. And that makes a huge difference, I think, in the success of those gardens. I have to say that in my Central Valley California garden, which is very hot and dry, I use lots of organic mulch. But I have learned that there are some plants I cannot grow in that organic mulch because it holds too much moisture in the soil and potentially close to the stem. I tried to keep it away from the stem but I'm not in total control. And so some plants just don't do well in that environment. Other plants love it and and so that limits my plant palette. On the other side of it, a gravel mulch that's four to five inches deep is also going to limit your plant palette, regardless of where you do it. But in places where there is summer rain and humidity, you'll have a broader plant palette that you can plant in that four to five inches of gravel.

Farmer Fred  14:55  

The link that we'll have refers to to a PowerPoint that the director of the Olbrich Botanical Garden did about their gravel gardens. And if you want to learn more about gravel gardening, you ought to listen to what he has to say about the plant palettes that can be used and the care that they take during the offseason. And one thing that he pointed out was that the staff there do a big job in the wintertime of removing dead organic matter and making sure that there is nothing for weed seeds to lodge in. 

Debbie Flower  15:32  

Regardless of what you mulch with, weed seeds are going to land on that mulch. And if there's any organic matter or any source of water, they will germinate and grow. And that's to me it's more difficult to get the organic matter out of gravel than to just let it melt into the existing organic mulch that I use in my gardens. By the way in that PowerPoint, he talks first about meadow gardens, too, and it's a long PowerPoint, over an hour. Start in the second half if you only want to hear about gravel gardens. ,

Farmer Fred  16:04  

It's in the last 15 minutes, quite near the end. You can see it and you learn a lot there. He had a lot of interesting tips. And he said that when they bring in plants, one gallon plants from nurseries, one thing they do is they scrape off the top two inches of soil, because that's where you're going to find most weed seeds.

Debbie Flower  16:25  

He's probably right, you're going to find most weed seeds in the top of the soil in a containerized plant. But that sort of makes me shiver to remove the top two inches. There are going to be roots there, potentially feeder roots there, that you're going to expose and damage potentially. And they may die in a harsh environment like the Southwest or Central California in the summer. That plant needs all the roots and moisture that it can get. In a more forgiving environment like Madison, Wisconsin in summer, which has more mild temperatures than we do and has summer rains and humidity, the plant may survive better.

Farmer Fred  17:02  

They are beautiful looking gardens back there. More power to them, if they can do that. I just think that in USDA zone nine, especially, it would be a struggle in nine and higher. Yeah, if you want to try it, I'd say try it in a small area first.

Debbie Flower  17:17  

A small area, where you want the plants to do well, there are succulents, plants that store water themselves. Hens and Chicks, Sedums, Dudleyas, those kinds of things. And Alpine plants that grow high. An alpine plant is a plant that grows high up on a mountain, potentially above the tree line, where there's not enough soil to support a tree. You have scree up there and scree is broken down rock. So those plants do very well in that area. So if you want to try a section and they're very interesting, they can be very beautiful, with very interesting flowers. And they tend to be smaller plants. So you can get a lot of them into a small space. It would make a really cool garden to put somewhere that you get up close if you have an outdoor sitting area or something.

Farmer Fred  18:06  

They also have a lot of ornamental grasses, which looked fabulous by year three.

Debbie Flower  18:10  

 And he talked about prairie plants, which grow in the Midwest, and they have tap roots. Generally, plants coming out of containers don't have tap roots. But the plants we're talking about here are herbaceous plants and grasses. They can regrow their tap root, the grasses for sure. When you see pictures of prarie plants, I wouldn't call them so much tap roots as they just have a very extensive root system.

Farmer Fred  18:39  

So again, the differences between a rock garden and a gravel garden. Out here in California, we are familiar with rock gardens. Rock gardens are shallower, maybe one inch or two inches worth of river rock really inch and a half river rock.

Debbie Flower  18:51  

And often accented with larger rocks.

Farmer Fred  18:55  

And the gravel garden is just that. It is made out of pea gravel, or in the case of what they did back in Wisconsin, seven-sixteenths of an inch of quartzite. And it has to be not sharp, in order for you to be able to walk on it, moreso for your pets to walk on it, or to work it with your hands. And that's the other thing too, that he pointed out. When they are cleaning up those areas in the wintertime, everybody has knee pads.

Debbie Flower  19:21  

Mm hmm. Yes. Knee pads are a good idea to get used to wearing when you're in the garden anyway. I can attest to that, having had to have one of my knees replaced, because I didn't always wear knee pads. But the other thing, another point he made was that you don't taper the gravel to the edge of the garden. You have some sort of edging and he shows you a whole bunch of different types of edging that are four to five inches tall, so the gravel remains consistently deep.

Farmer Fred  19:51  

That would be important. You need a barrier to keep it in place, so consider building sort of a little raised bed. For a gravel garden, if you're going to try that, and again, it's going to be more expensive because you're using four to five inches worth. And if you go out and price a ton of pea gravel, well, I guess you can borrow on your IRA to pay for it, but don't do that.

Debbie Flower  20:16  

And then delivery and then shoveling it.

Farmer Fred  20:21  

Rock gardens, gravel gardens. If you're going to try it, try it on a small scale first.

Debbie Flower  20:27  

See how it goes and let us know. 

Farmer Fred  20:29  

Debbie Flower, thanks so much for rocking down with us.

Debbie Flower  20:32  

Very interesting stuff. Thank you.

Farmer Fred  20:38  

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Farmer Fred  21:39  

Have you taken a look at the Garden Basics with Farmer Fred newsletter yet? It’s a deeper dive into what was discussed on the week’s two podcasts, along with more great gardening information. Think of it as going, “Beyond the Basics”.  In the current edition of the newsletter, we fill in the gaps and tackle the questions raised in this week’s podcasts. From Tuesday’s Episode 166, Debbie Flower warns us about using commercial potting soil in the ground around new plantings. From the Friday, February 11th podcast, episode 165, we do a deep dive into soil testing kits as well as online soil testing services, and we take a look at what your citrus tree leaves might be telling you about their health.  You can find a link to the Garden Basics with Farmer Fred newsletter, Beyond the Basics, in the podcast show notes; or, at Farmer Fred dot com; or, by going to substack dot com slash garden basics.  Think of it as your garden resource that goes beyond the basics. It’s the Garden Basics with Farmer Fred newsletter. And it’s free. Please subscribe and share it with your gardening friends and family. The Garden Basics with Farmer Fred newsletter. And thank you for listening. 

Farmer Fred  22:56  

We have a quick tip for you. Debbie Flower is here, our favorite retired college horticultural professor. Let's talk a little bit about cool season annuals. They grow in the winter in USDA zones nine and eight and parts of seven. They can perform, they can bloom, they can grow.

Debbie Flower  23:12  

Yes, we can have some very colorful gardens. Even in winter.

Farmer Fred  23:15  

Even though the temperatures might be down in the 30s and 40s and 50s. The soil temperature is still 40-45 degrees. So there's some activity going on. 

Debbie Flower  23:24  

That's right. Roots are still active, just not fast. But things are still going on, the plants are still able to absorb.

Farmer Fred  23:30  

Do you need, then, to fertilize cool season annuals?

Debbie Flower  23:35  

"Need" is a strong word. And it would apply to fertilizing anything really. Plants make their own food and they use nutrients that they get through the environment and absorbed through their roots to make that food. The time to fertilize is when they show you that they don't have enough of those nutrients. And that is when they have very small new leaves and they're losing all of their older leaves down at the bottom or closer to the trunk or they're all turning yellow, that would be a nitrogen deficiency. Or when you're seeing different streaks of yellow, let's say, in the leaves. That could be a micronutrient deficiency, the plants should be flowering, producing flower buds and opening them and it's not or the plant should be producing fruit and the fruit should be expanding. And it's not. Those are deficiency symptoms. And that's when you apply nutrition, which is in the form of fertilizer in the cool season. All those processes are very slow in the plant. And if you have soil that has been mulched with organic matter for a long time, long enough  that the organic matter has started to break down and release nutrients to the soil, you typically will not need to fertilize the winter annuals.

Farmer Fred  24:48  

That makes a lot of sense too. Because mulch is a slow release fertilizer as it breaks down. It's feeding the soil and if you've had that mulch for a long time, like you say, then your plants are slow. Slowly, slowly being fed. And I think we all prefer to be fed, slowly slowly.

Debbie Flower  25:05  

It's painful to eat too much at one sitting. Yeah, exactly. And a plant can show that symptom as well.  They can burn when you give them too much fertilizer. Yes, cool season annuals need nutrition, because they're alive and they're flowering or fruiting or whatever it is you you have them for, even just growing them for their showy green parts. But do we need to add fertilizer only if we see deficiency symptoms.

Farmer Fred  25:30  

And it can't hurt to do a soil test, to find out exactly what the soil needs. And you can buy soil tests that do more than just measure pH, which you get in the less expensive soil test kits. The better ones will also measure nitrogen, phosphorus and potassium. But you can go beyond that and  buy a more expensive soil test kit to check for micronutrient deficiencies.

Debbie Flower  25:50  

Yes, you can. And if you have any sort of a chemistry interest, or someone in your family does, it's lots of fun to do these tests. You mix chemicals and shake things and add soil and in time it changes color. It's lots of fun.

Farmer Fred  26:04  

Or if you're like me, a D student in high school chemistry, you can send off a soil sample to inexpensive places that come back with a very extensive soil test reports, such as the University of Massachusetts Amherst, and Colorado State University provide. Just do an internet search for "soil test UMass Amherst" or "soil test Colorado State" and the details will pop up on for $15-20 -$25 you can get a complete soil test.

Debbie Flower  26:32  

And they will give you the directions on how to take the soil samples etc.

Farmer Fred  26:36  

Yes, they will.

Debbie Flower  26:37  

Follow the instructions exactly. 

Farmer Fred  26:40  

Yes, exactly. Don't do shortcuts. Well, we've learned something about cool season annuals today. Feed them with mulch.

Debbie Flower  26:48  

Yeah, prepare your soil for them.

Farmer Fred  26:50  

There you go. Debbie Flower, thanks so much.

Debbie Flower  26:51  

Thank you. You're welcome.

Farmer Fred  26:57  

Garden Basics comes out every Tuesday and Friday. It's brought to you by Smart Pots. Garden Basics is available wherever podcasts are handed out. And that includes Apple, Iheart, Stitcher, Spotify, Overcast, Google, Podcast Addict, Cast Box, and Pocket Casts. Thank you for listening, subscribing and leaving comments. We appreciate it.

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