Cercis canadensis can be a tricky plant to propagate, but at Hidden Hollow Nursery, budding on reliable rootstock has proved successful.


Cercis canadensis can be a tricky plant to propagate, but at Hidden Hollow Nursery, budding on reliable rootstock has proved successful.
PHOTOS COURTESY OF ALEX NEUBAUER.

At Hidden Hollow Nursery in Belvidere, Tenn., we specialize in high-quality, grafted, bareroot liners, and we are always on the lookout for new, unique plants that are also commercially viable. My father, Harald, and I own and operate this small nursery located on the rich, loamy valley soils of the southern Cumberland Plateau. The company was established in 1982, and while I grew up on the nursery, I officially joined the family business in 1998. At Hidden Hollow, one of our goals is to produce new and/or hard to propagate plant material.

In order to reproduce new and superior plant cultivars – those that have been selected for specific traits, such as flower or leaf color, improved architecture or disease resistance – the plants must be asexually propagated. This can be accomplished by any number of methods, but we’ve found that many plants we grow do not root easily from cuttings or other methods. Our approach, then, is budding and grafting.

Budding and grafting is a skill (or maybe an art form) that has been practiced since before 2,000 BC in China and has persisted until our modern time as an effective method to reproduce desirable plant clones. “Grafting” is a blanket term for many different techniques of attaching the tissue of one plant to another and then forcing it to grow. Here we’ll focus on the propagation of Cercis canadensis (eastern redbud) by budding at our nursery in middle Tennessee. Cercis is a difficult genus to propagate, and there are many new selections that have been made in the last decade or so, with many more under evaluation for the future.

Begin with rootstock

It takes us two years to successfully transform a redbud seedling into a desirable and uniform cultivar that is ready for sale as a liner. We begin the process by purchasing a healthy and hardy, one-year-old rootstock that is approximately 12 to 24 inches in height and ranges in caliper from one-eighth-inch up to one-quarter-inch. We trim the roots to encourage branching and discourage one sided, or “J-roots.” The tops can also be pruned back to a uniform height for ease of planting. Planting takes place in late March into April using our small tree planter, which is attached behind a tractor. We use normal, tidy cultural practices such as band spraying preemergent herbicides, administering granulated fertilizer and regular watering through a drip irrigation system in order to ensure transplant success and to maintain vigor in our seedlings.

Scion wood

Scion wood is the branch with the buds from your known, desirable tree; this will be attached to your rootstock and become your future cultivar. It is of utmost importance to begin with the correct scion wood. Some Cercis cultivars are easily recognized by their physical appearance, yet others are not obvious until later in their life. One example of the importance of this happened to a customer one year we could not supply t200 ‘Appalachia Red’. Our customer purchased from a different supplier that did not take the critical step of procuring proper scion wood, so the next spring when they bloomed only two plants out of 200 were correct, proving to be a costly mistake for both parties. The best scions or bud sticks are the current year’s growth. These should be approximately the size of a pencil, allowing for some variation to match with your rootstock. They can be collected from your current, or from stock plants maintained on the nursery.

We normally collect our ripe bud sticks early in the morning, remove the leaves with a pair of clippers, wrap in a wet towel, and put them in an ice chest until we use them up later in the day.

Tools

The main tools required for a successful budding procedure include a good, sharp horticultural knife and material to tie and hold the buds in place on the rootstock until callusing occurs. This is usually plastic wrapping tape. There are many knife makers out there, but we prefer to use Tina brand knives. They are of high German quality, much like my father.

There are a few other items that help to make the arduous, but rewarding task of budding just a little more comfortable. Our entire budding season usually lasts for around eight weeks, so we indulge ourselves. One of our favorite “tools” is a shade buggy – with or without a radio. Built atop four bicycle wheels, this is a metal frame supporting a white sheet that you wheel along to provide shade. I highly recommend it! Other items to keep on hand include a box of Band-Aids for the “greenhorn budder” and a bottle of Aleve for your back. What would also help considerably – but is beyond our control – is proper alignment of the moon and stars, because sometimes all conditions seem perfect yet the success can be less than.

How to: the slicing and dicing

As we all know, the learning curve on a nursery is huge. The way you started is not necessarily the way you work now, and what works for some may not work for others. We have successfully propagated Cercis by other techniques, but we have found chip budding to be the most practical method for our production. We bud from mid-August to late September when the rootstock is in a good state of growth and “juicy,” in budder’s lingo. The scion wood is also still growing, but the buds are well-formed and the bark has hardened, so it is not easily skinned.

To begin the budding procedure in the field, you must bend at the waist and back up to the rootstock, or straddle the row with the bud stick in the left hand and knife in the right (for a right-handed person). We prefer to move to our left along the row with our wrapper close by on our right side. I first cut the chip out of the rootstock 1 to 1½ inches above the soil line. I draw the knife horizontally across the rootstock at a steep angle to make the first cut that I call the heel. The second cut is made approximately one-half-inch above the first, drawing the knife through the plant just below the bark and skimming just above the pith to reveal the cambium. The order can be reversed for personal preference. This chip of bark is removed and discarded, leaving a long, inverted U-shape.

Next, with the bottom of the bud stick toward my body, I cut a matching chip that contains a bud to replace the one removed from the rootstock. In this procedure, I usually make the long, smooth cut first, beginning above the bud and ending just below the remaining petiole. I slide the knife out from below the chip and make the second, steeper and shorter heel cut to release the chip from the scion. I then grab the chip between my thumb and index finger and gently push it onto the cut rootstock. My father grabs the chip between his thumb and his knife; again, this is personal preference. In a perfect world, the greenish cambial ring on your chip will exactly line up with the cambial ring on the rootstock. “Getting it right” most likely will occur sometime after 100,000 repetitions or more.

Remember, perfecting your technique in the beginning supersedes speed. You must take time and fight for every bud to live. A good stand is the ultimate goal. Speed comes with practice.

Once I feel comfortable that I have made a good match, the wrapper finishes the procedure. With the left hand, he takes a single tab behind the rootstock and stretches one corner around to the front and just below the bud and holds this against the rootstock. With his right hand, he stretches the tab around the right side of the rootstock and over the first corner of the other side of the tab to initially secure it. He then continues to wrap the tab around and over the union until the entire site is covered, usually in four to five wraps, stretching the tab as he goes. To finish, it is as simple as tearing the tab while pulling against the rootstock or using the entire tab. A proficient budder can skillfully accomplish 100 to 150 buds per hour, depending on cultivar. Straight, plump budsticks are much faster than skinny, zig-zag sticks.

Aftercare

Once budding is completed, care for the rest of the year is minimal. It’s important to maintain the plants’ vigor and health, and to keep them weed-free for the next few months until the onset of winter and dormancy.

After a few weeks, it is possible to check the success of your budding. The tape biodegrades and splits open. At this time you can see if the buds have attached successfully, or if they have been pushed out. A nicely attached bud shows signs of callus around the edges and is slightly sunken in the center. It should have normal, healthy color – not dry or brown. You can also check your take and decide if it would be beneficial to re-bud the unsuccessful plants. At our nursery, we typically see a 75 to 90 percent bud success rate. This, of course, does not mean we will ultimately harvest these plants, as there are many factors to overcome, including wind breakage, worker damage, animal and insect damage, harvest damage, and early and late freezes (during the Easter 2007 freeze, we lost 80 percent of all crops). Again, you must fight for every tree.

The next year

As fall turns to winter, we get busy with the harvest of finished trees for spring sales. The healed-in buds lie dormant through the cold of winter. In mid- to late February, we come back to our rootstock with bud attached, and we remove the top of the rootstock with pruners, just above the top of the attached bud. The cut slopes from the top of the bud straight back at approximately a 30-degree angle. This step is very important so that the cut will callus and close up almost totally by the end of the growing season, making the plant straighter, stronger, and more resistant to disease – and of overall higher quality.

When the buds break dormancy, all the energy of the established rootstock is forced into the one remaining bud that we placed there. At this point we apply fertilizer, and shortly thereafter we place a fiberglass stake to encourage straight stems and to prevent wind breakage. Removing the top also forces many shoots, or suckers, to arise from the rootstock below the bud union. These must be removed by pruning close to the rootstock. This is done up to three times per season. By the third pass in mid-August, few shoots are found and the new clone is growing strong. We tie the leader to the stake and, depending on growth rate, we remove lower branches approximately every two weeks from May through August. I estimate that we go over each tree nearly 20 times in two growing seasons: This includes trimming the roots on the rootstock, planting, budding, wrapping, staking, cutting back the top, removing suckers and pruning, taping a minimum of five passes, harvesting, grading, bundling, storing, and final shipping. In addition, we perform a spray regimen for pests.

Our yield

Cultivar buds attached to summer rootstocks yield plants of 4 to 7 feet with a stem caliper of ¾ to 1¼ inches by the end of the following growing season. These are ready to be sold as liners. Other methods in use yield mixed results. Rooting stem cuttings is reportedly difficult and varies between cultivars. One study reported a maximum success of 83 percent on only one cultivar, although this appeared to be a deviation from the norm and well-above the success reported in other investigations.

Cercis chinensis do appear to root easier, but two-year-old, bed-grown plants are smaller. While I have no personal experience, I know Cercis are being produced from tissue culture. They also tend to be small (at least according to my sources) and are not readily available to the trade, with limited cultivars being produced. It would take a minimum of one year (and possibly up to two) to equal the size of a budded liner.

Our personal experience and the lack of plants available to the market by other means of propagation leads us to believe that open-ground chip budding on established rootstocks is a very successful and viable method for producing cultivars of Cercis canadensis and C. texensis liners in middle Tennessee.

Important new Cercis cultivars

  • ‘Ruby Falls’ PPAF – superb hybrid of Lavender Twist ‘Covey’× ‘Forest Pansy’ resulting in the first weeping, purple-leaved redbud available to the market; from Dr. Dennis Werner’s decade-long breeding program at North Carolina State University (NCSU).
  • ‘Merlot’ PPAF – C. texensis × ‘Forest Pansy’ hybrid with thick, glossy purple leaves that maintain their attractive appearance late into the growing season; a denser, more heat-tolerant and more upright alternative to ‘Forest Pansy’; another product of Dr. Werner’s breeding program.
  • ‘Ace of Hearts’ PP#17161 – compact, symmetrical cultivar with leaves one-third the size of the species.
  • ‘Alley Cat’ – superior white variegation that persists throughout the season and does not burn.
  • ‘Kay’s Early Hope’ – blooms 10 days earlier than other redbuds and blooms persist later as well; named for the late NCSU basketball coach Kay Yow, as it blooms in time for the NCAA tournament.
  • ‘Little Woody’ PP#15854 – compact form with smaller, bluish, textured leaves.

Alex Neubauer is the owner of Hidden Hollow Nursery, Belvidere, Tenn., a small, family business started by his father, Harald, in 1982. Hidden Hollow focuses on specialty grafted woody ornamentals. After graduating from the University of North Carolina, Asheville, with a degree in Environmental Science, Alex returned to Belvidere to join his father full-time in 1998. Alex and Harald are always on the lookout for useful, new plant material and enjoy helping friends and colleagues bring new plants into commercial production. He can be reached at alex@hiddenhollownursery.com.