Hey Bartender…Give me Another Shot of Winter

I had to chuckle as folks on several Facebook plant groups were wringing their hands in worry prior to the recent cold snap, while we were secretly hoping for even colder temperatures than forecast.

JLBG registered three consecutive nights in the teens recently; 11F, 19F, and 19F. While this was certainly not abnormal for our area, folks with very short memories thought the horticultural world was coming to an end. In reality, we recorded similar temperatures in the winter of 2017/2018, albeit a week later that year.

When we first started the gardens at JLBG, we were squarely on the Zone 7b side of the Zone 7a line. We are now on the Zone 7b side of the Zone 8a line. In order words, we have shifted about 1/4 of a hardiness zone. Since 2018, JLBG has registered three consecutive Zone 9a winters, so it’s not surprising the new gardeners or those with short memories start assuming that all kind of plants are reliably winter hardy, which is not the case.

We long for cold temperatures because we want and need good winter hardiness data, and while mild winters may be enjoyable to us Homo sapiens, we don’t learn anything about plant hardiness from those winters. So, here are a few things we learned this year.

Agave bracteosa ‘Stingray’ is the most winter hardy of all brightly variegated agaves we’ve tried. Here is our plant looking quite lovely after our 11 F cold.

Agave bracteosa ‘Stingray’

Agave weberi ‘Stone Cold Austin’ is Patrick McMillan’s collection of Agave weberi from Austin, Texas. We’ve tried Agave weberi a couple of times prior, and could never get it through one of our milder winters. Patrick’s original plant at Clemson got large enough to flower there, so we’re hoping for the same. The older foliage is showing damage from 11F, and will most likely be lost, but the bud seems fine so far.

Agave weberi ‘Stone Cold Austin’

We’ve never had any luck with any of the dwarf Agave lechuguilla mutants we’ve tried in the garden, but this new one, shared by plantsman Hans Hansen, that we call Agave ‘Tater Tot’, had no problem with 11F. These are often sold as Agave x pumila, which actually doesn’t exist. Everyone assumed that A. x pumila was a hybrid, but when one in Europe recently mutated back to the original form, it turned out to be nothing more that a super dwarf form of Agave lechugullla.

Agave lechuguilla ‘Tater Tot’

Mangave ‘Racing Stripes’ is a plant we had high hopes for in terms of winter hardiness, but we had not had a cold enough winter to get good data. Our only reservation was that it contains genes from the tropical Agave gypsophila. Thankfully, our plant came through the 11F freeze in reasonably good shape. The wrinkled nature of the older leaves are indications of cold damage that will show up in a few more days, but the core seems intact and should re-grow.

Mangave ‘Racing Stripes’

We fully expected Bambusa multiplex ‘Green Giant’ to be defoliated after 11F and the stalks killed to the ground, but our fully exposed clump still looks like it’s mid-summer…at least from the north side.

Bambusa multiplex ‘Green Giant’ – north side undamaged

On the south side, the same clump has fried foliage. There are typically two causes for such damage. One is wind desication when the winds are blowing from a single direction and the ground is frozen, making it impossible for the plant to replenish water lost through the foliage. During the time that our ground was frozen, our winds were coming from the West, so that wouldn’t account for damage only on the south side of the plant.

In this case, the more likely scenario is that this is due to sun scorch when the soils was frozen, since the damage is on the south side. If the canes are indeed undamaged, as it appears, new leaves should reflush in spring.

Bambusa multiplex ‘Green Giant’ – south side, sun scorch damage

We didn’t hold out much hope for the Mexican palm, Brahea decumbens, but it sailed through 11F unscathed.

Brahea decumbens

Since we know that genetics matters, we will often plant more than one clone of a marginal plant like a new palm. Below are two seedlings of the small-seeded European Fan Palm, Chamaerops humilis var. microcarpa. The first shows significant foliage burn, while the second plant, growing nearby shows no damage after 11F.

Chamaerops humilis var. microcarpa with foliar damage
Chamaerops humilis var. microcarpa undamaged

The hardiest of all Sabal palmetto forms are those from NC’s Bald Head Island. Our plant from there came through the cold unscathed. We expect many local businesses and even homeowners who purchase large trunked forms directly from Florida growers will probably be in for a disappointing spring.

Sabal palmetto ‘Bald Head Island’

All of our hardy cycads have assumed the straw-color we see every year when the temperatures drop below 18 degrees F. The plants are fine, but we recommend waiting to remove the dead fronds, since doing so now, can cause the new foliage to emerge in the middle of winter, which is never a good idea. April 1 is our target date to remove the fried foliage.

Cycas x panzhioluta

One of the real surprises was the fried foliage of Viburnum ‘Moonlit Lace’, where it was growing in full sun. The same plant growing in shade looks untouched. The stems are fine and the plant should re-sprout fine, but gardeners who grow this in full sun may be disappointed.

Viburnum ‘Moonlit Lace’

This is the coldest temperatures we’ve seen since planting Patrick’s hardy selection, Opuntia microdasys ‘Dripping Springs’. Our clump looks great after the cold. It’s hard to imagine that this clone is so much more winter hardy than any of the other forms of this species that we’ve tried previously and killed at much warmer temperatures. Although we don’t offer this for sales, I’ll remind you of our great prickly pear cactus giveaway at our Summer Open Nursery and Garden in July.

Opuntia microdasys ‘Dripping Springs’

The Mexican Sedum praeltum looks a bit sad, but actually seems to be fine with sound buds up and down the stem. This little-known perennial forms a plant that looks almost exactly like the tender Jade plant, Crassula ovata.

Sedum praealtum

Lastly, our patches of Living Stones, Lithops aucampiae, sailed through 11 degrees F. I wonder if we can ever get all the disinformation on the Internet regarding their tolerance to cold corrected.

Lithops, living stones, are much more winter hardy than reported. The key is keeping them dry, planted under an overhang in our crevice garden.
Lithops aucampiae

Supersize Me

In 2014, we decided our goal for the years’ century plant breeding project was to see how large a Zone 7b winter hardy agave we could create. We had seven agaves flower that year, but only two had the epic proportions we required.

One of those was a selection of Agave x protamericana from a Yucca Do collection in Northern Mexico. By the time of flowering at 15 years of age, it had reached 5′ tall x 9′ wide.

Agave x protamericana and Agave americana are the two largest blue-foliaged agaves, but only Agave x protamericana is winter hardy for us, here in Zone 7b, since it also has some ancient genes from the slightly hardier Agave asperrima, which adds slightly to its winter hardiness. You can distinguish the two plants by feeling the back of the leaves. Agave americana has smooth leaf backs, while Agave x protamericana has sandpapery leaf backs. The largest size listed for Agave americana in Howard Gentry’s Agaves of Continental North America, is 6′ tall x 12′ wide.

A large growing agave with blue green foliage growing in our zone 7b garden.
Agave x protamericana YD45-79

At the same time we had a blind flower shoot on our giant Agave x pseudoferox ‘Bellville’. Agave x pseudoferox is another ancient Mexican hybrid in need of a DNA workup. We think its probably a hybrid of Agave x protamericana with Agave salmiana var. ferox and possibly Agave gentryi). Commercially, it’s usually called Agave salmiana var. ferox, which is similar in appearance, but with absolutely no winter hardiness.

Prior to full flowering at 15 years of age, our giant specimen of Agave x pseudoferox ‘Bellville’ had reached a mature size of 4′ tall x 8′ wide. We were able to make the cross prior to it fully flowering, by using something we mentioned above that we call “blind shoots” or boners.

Being monocarpic plants, the rosettes of most agave species die after flowering, but side shoots are an interesting phenomenon we see on all of our Agave x pseudoferox cultivars and hybrids. These “blind shoots” emerge from underground stolons instead of from a rosette. They are much shorter than normal flowering shoots which emerge from the rosettes (2′ tall vs. 20′ tall), and they have no impact on the life expectancy of any of the rosettes.

In the case of Agave ‘Bellville’, our plant began producing blind shoots five years prior to the clump producing a full size, rosette-based flower stalk. The beauty of blind shoots is that they breed and pass along characteristics of the parent without the need for a tall ladder.

Agave 'Bellville' is another large blue green form that produced "blind shoots" which are flowering shoots produced from the underground stolons.
Agave x pseudoferox ‘Bellville’

We gave our hybrids the seed strain cultivar name, Agave ‘Bluebell Giants’. From these, we selected 23 clones, which were planted in the trial fields in 2016. Of those, only 4 survived our subsequent trials for winter hardiness.

Our seed crop of the hybrid from the two large growing blue green agaves.
Agave ‘Bluebell Giants’

Our best and most winter hardy seedling from the cross pictured below is now 6 years old in the garden. We’ve given this the name Agave ‘Supersize’. It has achieved a size of 6′ tall x 8′ wide in that time. To put this in perspective, it is larger at 6 years old than both parents were at 15 years old. If Agave ‘Supersize’ waits until age 15 to flower, it could easily reach more massive proportions that any Zone 7b winter hardy agave in existence.

A clonal selection from the hybrid seedlings, A. 'Bluebell Giants' that has passed our hardiness trials.
Agave x pseudofox ‘Supersize’

Makin’ Mangaves

While we leave all the fancy mangave creations to our friend Hans Hansen at Walters Gardens, we continue our work on creating more winter hardy (to 0 degrees F) hybrids. Over the last couple of years, we’ve made several crosses using some of Hans’ hardiest Agave ovatifolia based F1 generation selections, like xMangave ‘Blue Mammoth’ and xMangave ‘Falling Waters’ and crossing them back onto Agave ovatifolia.

The F1 mangave hybrids from Hans’ work, have all lost the monocarpic trait of pure agaves, meaning they will not die after flowering. We are curious what will happen if the hybrids have 2 parts agave and one part manfreda. With most of our crosses, we grow 100-200 of each into 1 qt pots, which allows us to do an initial culling after seeing the juvenile foliage traits.

The photos below are from that process, which happened this week. This is a cross of xMangave ‘Falling Waters’ x Agave ovatifolia ‘Frosty Blue’. The first image shows the diversity in the seedlings. All plants have some degree of glaucous foliage…some more toward blue and others with purple spotting that comes solely from the Manfreda parent. It was interesting that the F2 plants still showed some degree of purple spotting…probably around 5% of the plants.

Mangave seedling variability within a F2 generation cross.
x Mangave ‘Falling Waters’ x Agave ovatifolia ‘Frosty Blue’

From a batch of 100-200 plants, our goal is to select 10% for the next round of in ground trials. We focus on selecting at least one plant for each desirable trait. Those traits include: size (dwarf or large), leaf undulations, spotting density, best blue color, leaf twisting, leaf length, leaf width, overall form, best spination, and variegation.

Below are some of our final selections for the next phase of trials. These will be up-potted into 3 quart pots and overwintered indoors, since we’re already too late for planting outdoors this year. These will go into the ground in spring, after the danger of frost has passed.

Mangave seedlings selected for in ground hardiness trials.
x Mangave ‘Falling Waters’ x Agave ovatifolia ‘Frosty Blue’
x Mangave and Agave hybrids overwintering in a heated greenhouse
x Mangave and Agave hybrids overwintering in a heated greenhouse

Agave ‘Prince of Whales’

Our 2016 century plant hybrid is looking quite lovely in the garden this month. This plant, which we named Agave x victorifolia ‘Prince of Whales’, is a hybrid of the Whale’s tongue century plant, Agave ovatifolia (male parent), and the Queen Victoria century plant, Agave victoriae-reginae (female parent).

Since both parents are non-offsetting, this means that the offspring will grow to maturity, flower, then die. Consequently, in order to be able to propagate and share, we will have to drill out the central core of the plant to trick in to offset. While this ruins the appearance of the original, it’s the only way for this to ever be shared and preserved. This plant has been in the ground since 2018, so we expect to have another eight years (guessing) prior to flowering. Consequently, so we’ll probably gamble on waiting a few more years before performing surgery. Winter hardiness is Zone 7b-10b.

Agave x victorifolia Prince of Whales
Agave x victorifolia ‘Prince of Whales’

Below is a photo of both parents.

Agave ovatifolia
Agave ovatifolia
Agave victoriae-reginae
Agave victoriae-reginae

Stingray in the Garden

We love the spineless Agave bracteosa ‘Stingray’ in the garden. We’ve had these dotted throughout the garden since 2017, and so far, with good drainage, they’ve handled our winters quite well, which is certainly not normal for a variegated century plant. This particular species prefers part sun to light shade. Hardiness is Zone 7b/8a and warmer.

Agave bracteosa Stingray in the garden
Agave bracteosa ‘Stingray’ in the garden

The Look of Love

If you’re able to visit during this years spring open house, it will be hard to miss the look of love in the air. We have a record 20 century plants in spike in the garden…a number far surpassing any flowering record we’ve set previously.

Agaves are a genus of mostly monocarpic plants…they live their entire lives to flower once, then after experiencing a giant-sized orgasm, they fall over dead. In the wild, many species take up to 100 years to flower, which is why the name century plant stuck as a common name. In our more rainy climate, our century plants typically flower in 12-15 years. Several of our current crop are actually less than a decade old, but their enormous size has already been achieved, so they’re ready to reproduce.

Some species of agaves offset, and in this case, only then central rosette dies, and the offsets continue as is the case with bromeliads. Those agave species which never offset are one-and-dones, but hopefully will leave behind a plethora of seed for the next generation. From the start of the spikes to full flower is usually about 8 weeks. Below are a few of our babies in spike.

Agave ovatifolia ‘Vanzie’
Agave x ovatispina ‘Blue Arrows’
Agave lophantha JLBG-01
Agave x loferox JLBG-014
Agave x pseudoferox JLBG-176

Snowgaves

We’ve “enjoyed” frozen precipitation for three consecutive weekends this winter, with one producing a decent 3.5″ snow. There’s something magnetic about snow on century plants, that makes you grab your camera and snap away.

The white of the snow looks out of place on an agave, although it does wonders for accenting the architectural structure of the plant. We have worked for 35 years to identify and create agaves which are completely tolerant of such weather events. Below are a couple of our hybrids, created here at JLBG.

Agave x amourifolia
Agave x loferox

Sex for the Centuries

Since we are limited in the number of hardy century plant species, our only option for more agave diversity in the garden is to create it by crossing existing hardy species together. Here are a few of our recent successes.

Agave x amourifolia is a Plant Delights/JLBG creation from a cross we made in 2016 that combined the genes of three century plants, Agave ovatifolia, Agave lophantha, and Agave x pseudoferox ‘Logan Calhoun’. Our size estimates were that the offspring would mature at 3′ tall x 5′ wide. Here is one of our garden specimens photographed this week, which has already reached 2′ tall x 3′ wide.

Agave x amourifolia

Below is Agave x ovox, a 2017 cross of the two giants, Agave ovatifolia and Agave x pseudoferox ‘Bellville’. We expect this to get huge…perhaps 5′ tall x 10′ wide.

Agave x ovox ‘Large Ox’

Below is Agave x protifolia is a 2016 Mike Papay cross of Agave x protamericana x Agave ovatifolia. We also expect this to get quite massive.

Agave x protifolia

Below is Agave x ovatispina ‘Blue Arrows’, a 2016 Mike Papay cross of Agave ovatifolia x Agave flexispina. We would have expected this to be a mature size, but it’s achieved this in only 5 years, so we think we’re seeing some serious hybrid vigor.

Agave x ovatispina ‘Blue Arrows’

Below is Agave x ocareginae, our 2016 cross of Agave ovatifolia x Agave victoriae-reginae. Most likely, this elegant small grower will never offset.

Agave x ocareginae

Below is Agave x schuphantha, a 2015 Mike Papay cross involving three century plant species, Agave schidigera, Agave lophantha, and Agave lechuguilla. It’s formed a beautiful, symmentrical rosette, which should be getting close to mature size.

Agave x schuphantha ‘Wheel of Fortune’

Sibling rivalry

As a plant breeder, one of the cool things we get to do is observe the diversity that arises from a single cross. In some cases, the diversity shows up in the first generation (F1), while in other cases, the first set of offspring need to have sex with each other for the diversity in the offspring to reveal itself (Mendelian genetics). Fortunately, with agaves, we can see quite a bit of diversity in the F1 populations.

Below is a cross we call Agave x amourifolia, which is our cross of Agave ovatifolia, pseudoferox (salmiana var. ferox of Hort.), and lophantha. Here are three of our selected seedlings from that cross.

Plant #1 below is showing the large size of Agave x pseudoferox and the color of Agave ovatifolia (blue), with little visible influence of the narrow leaf, yellow-centered Agave lophantha.

Agave x amourifolia

Plant #2 below show more color influence from Agave x pseudoferox, but with the compact form influence of Agave ovatifolia.

Agave x amourifolia

Plant #3 below shows equal parts Agave x pseudoferox and ovatifolia, but also, what appears some leaf narrowing we would expect from Agave lophantha.

Agave x amourifolia

Below is Agave x flexiferox, created from a cross of the small Agave flexispina x the giant pseudoferox (salmiana var. ferox (Hort.). Plant #1 shows the small size of Agave flexispina, with the greenish coloration of Agave x pseudoferox.

Agave x flexiferox

Below, Agave x flexiferox ‘Megalodon’ shows the larger size and overall coloration from Agave x pseudoferox, with some added blue tones from Agave flexispina.

Agave x flexiferox ‘Megalodon’

Below is Agave x victoferox, a cross of Agave victoriae-reginae x pseudoferox. Plant #1 below shows the form and size of Agave victoriae-reginae with the color of Agave x psedoferox.

Agave x victorferox

Hybrid #2 below shows the teeth from Agave x psedoferox (victoriae-reginae has no teeth), and a size intermediate between the two parents.

Agave x victorferox 2

Hybrid #3 below shows a larger size and more teeth due to more genes from Agave x pseudoferox. The teeth are much smaller because of the Agave victoriae-reginae genes. The splendid compact form also comes from the Agave x victoriae-reginae parent. This cross almost resembles the Northern Mexican Agave montana.

Agave x victorferox 3

We hope this gives you a small peek into the world of plant breeding and the subsequent evaluation and selection process.

I’ve fallen and I can’t get up

This summer, two of our spiking clumps of Agave ovatifolia became dislodged from the ground during a violent thunderstorm. We wondered if they would still set viable seed despite being without roots, since the energy built up from 15 years of growth was still in the foliage. We made several crosses without having to set up a ladder and it appears that we’ve got good seed set. Nature is amazingly in its desire to survive.

Striptease in the Succulents

Agave x striphantha ‘Striptease’ is a JLBG creation from a 2013 cross of Agave striata and Agave lophantha. Both parents are 30 year survivors here in the garden, so we wanted to see what a combination of genes looked like. Also, Agave striata is the only hardy agave species, whose main crown doesn’t die after flowering. So far, this gem is 3′ wide, and like the Agave striata parent, it offsets from the crown and doesn’t sucker like Agave lophantha. It’s looking like a flower spike may be imminent, so perhaps we’ll have our flowering question answered soon.

Agave x striphantha

When creating hybrids, especially with plants like agaves, it takes many years to know exactly what the offspring will look like. We have a pretty good guess, since we’ve done this for so long, but here’s an updated photo of a cross we made in 2013 of Agave striata x Agave lophantha. The hybrid, that we call Agave x striphantha is now 3′ wide, which is the same width of the Agave striata parent. We expected the hybrid to stay a bit smaller, but it did not. What we still don’t know is what will happen when it flowers. Agave striata is the only hardy species that doesn’t die after flowering, while the flowering rosette of the other parent, Agave lophantha cashes it in after its sexual encounter. Hopefully, it won’t be long before we know about the hybrid, and hopefully it will produce viable seed.

Learn more about growing agaves.

Agave x striphantha (striata x lophantha)
This is the Agave striata parent
This is the Agave lophantha parent.