Redbud Potting Experiment

[0soyoung]

I have just potted 8 Eastern Red Bud (Cercis Canadensis) seedlings. My experiment design (similar to what I described in the “Let’s All Get Some Answers and Not Wait for the Book” thread) is given by the following table and notes.

tree	repot	rhizo	cuts	shoot pru	defol
1	-	-	-	+	+
2	+	-	-	-	-
3	-	+	-	-	+
4	+	+	-	+	-
5	-	-	+	+	-
6	+	-	+	-	+
7	-	+	+	-	-
8	+	+	+	+	+

o repot ‘+‘ = Aug/Sep
o repot ‘-‘ = spring
o rhizo ‘+‘ = nested clear orchid pot & proLeague
o rhizo ‘-‘ = MVP in black pot
o cuts ‘+’ = cuts at stem base done at repotting
o cuts ‘-‘ = do nothing
o shoot pru ‘+’ = nip shoot tip to just remove terminal leaves
o shoot pru ‘-‘ = do nothing
o defoliate ‘+’ = remove fraction of leaves by cutting through petiole
o defoliate ‘-‘ = do nothing

This table simply says, for example, that tree 7 will be repotted Aug/Sep coming. I just potted it in a clear orchid pot of Turface proLeague. I made 4 lengthwise cuts around the trunk at the base of the seedling (the ideas behind this are to see the repotting time in future cross-sections of the trunks and to see if this induces trunk thickening). Later this season I will pinch the emergent shoot from buds near the apex and later (partially) defoliate it.

Because DanW suggested that repotting times are just before periods of root growth, I decided that I will try to measure root growth, in addition to monitoring the ‘above ground’ growth. I am using 6 inch clear orchid pots as mini rhizotrons to do this. Because it is difficult to discern roots from damp MVP, I filled these pots with dark colored Turface proLeague Heritage Red. Hence I have a new experiment factor, ‘rhizo’ that is a different soil and pot. These ‘rhizotrons’ are nested within a gallon size black plastic pot. Soon I will start looking at them weekly to measure the root length.

I am using Turface for two reasons. First is that MVP is my chosen planting medium. Second, is that it can be removed without disturbing the root mass by just gently agitating the tree roots in a bucket of water. This likely is also the case with non-compacting mixes (e.g., pumice, scoria).

I printed out the table below (with blanks for the weights and stem diameters) to keep track of what I was doing while potting the seedlings. I’ve filled in the measurement data that I collected in the process. I used a caliper to measure the stem diameter and a 1 gram resolution scale to weigh each (in retrospect, a finer resolution scale would have been better). Again, I selected the trees randomly with the simple intuitive procedure:

• Write the id numbers on a potting stick
• Put the sticks, numbered ends down, in a cup
• Pick a seedling/tree
• Pick a stick
• Perform the actions required for that id.

id	base dia (mm)	cuts	wt (gm)	clr pot
1	3.71	no	5	no
2	3.68	no	3	no
3	4.24	no	4	yes
4	3.1	no	3	yes
5	4.96	yes	4	no
6	3.26	no	4	no
7	2.98	yes	3	yes
8	2.82	no	3	yes

Lastly, I applied 1/2 teaspoon of Osmocote 14-14-14 to each.

 

[Poink88]

Curious if redbud leaves reduce much. We have lots of it here and I see descent stock in nurseries for (relatively) cheap. I love the late winter/early spring flowers on it but the leaves look intimidating.

Any input is appreciated. Thanks!

 

[gergwebber]

occidentalis seems to have a bit smaller leaves. NOT sure whats in texas. I have had an occidentalis in a 15 gallon pot going on its fourth year without a repot and the leaves are reducing.

I am not sure about them in a bonsai pot though... not to that point yet.

 

[0soyoung]

Progress - initial potting effects

All 8 trees in the experiment are alive and growing, but 3 of the 8 have dead ‘trunks’. That is, they only sprouted from near the soil line and did not sprout at all higher up on the stem/trunk. One happened to be in a shallow clear pot of Pro League and two in standard 1 gallon size pots of MVP. Clearly this is just a random assignment of the 3 trees with ‘dead trunks’.

There is no pattern that would link this phenomenon with the order in which I potted the seedlings, nor is there a pattern with regard to seedling weight and/or stem diameter. Interestingly, though outside the scope of this experiment, I also received two 4 foot seedlings as part of my deal with Arbor Day and one of them only sprouted from near the soil line.

Because of their ‘infantile’ state, I will not be applying the shoot pruning and defoliation treatments this year. These seedlings were ‘freebies’ as part of an Arbor Day deal and are only about 8 inches tall. The stem diameter at 4 inches above the soil is only about 2 mm and about 3.5 mm at 1 cm above the root collar.

 

[0soyoung]

Stem/Trunk Thickening

When I potted my Eastern redbud seedlings this spring I painted a mark about 10cm (4 inches) above the soil level and used this site for measuring the trunk thickness of each seedling every week or two with an inexpensive digital caliper. Each time I measured the seedlings, I measured each three times so that I could also gage my measurement accuracy and, therefore, whether the individual trees were indeed thickening while I was making measurements during the season.

I had serious troubles with stems getting snapped off either by my carelessness or that of some indigenous varmints. Neverthelss, I’ve rendered my data on the attached chart by the average thickness measured across 5 trees that didn't get their stems snapped and have normalized the data to represent the fraction of the seasonal increment (i.e., the normalized average thickness at the end of the season is 1). I’ve also represented the standard error of my measurements by error bars on the attached chart.

For me, the most interesting thing that comes from this is the red dashed curve of the rate of thickening (the slope of the curve through the data points). The rate of thickening increased during the season until ca. 18 July and has steadily declined since. This is quite interesting for folks that like to understand how trees work, but the only practical value I see to this for bonsai is to explain why wire is best applied in August or later in the season (alternatively, why ‘wire biting’ is so hard to avoid when one wire’s in the spring, before the solstice) – as though we didn’t know this already. For tree geeks, of course, it is significant that the time of maximum thickening occurs just after the summer solstice.

A couple of relevant details that I should add are that my measurement accuracy was about 0.036mm (surprisingly good) and that the average thickness increment for my redbud seedlings this year is about 0.82mm (which amounts to about a 40% increase in thickness for one growing season).

The attached plots show the growth rate curve against my daylight hours and my daily high/ave/low temperatures. Scholarly papers suggest that the maximum growth rate is controlled by daylight hours and that the dormancy period is controlled by (low) temperature.

 

[tmmason10]

Pretty cool experiment. Thanks for taking the time to do this.

 

[0soyoung]

The First Growing Season

For this past season, the only treatment that was applied was potting in Turface MVP (in one gallon black plastic pots) versus finer grained Pro League (in clear orchid pots nested inside one gallon black plastic pots). In pictures, the two groups look to me to be about the same. Maybe I should instead say that I don’t see anything that would make me choose to use Pro League over MVP (or vice versa) – which is to say there is no effect.

Redbuds in fine grained Turface Pro League

Redbuds in Turface MVP


The contrast may not be meaningful because I had serious troubles this year with stems getting broken off either by the help of indigenous critters in my yard or by my own carelessness (the past season’s stems seem to be quite brittle, much like late season twigs on Japanese maples). I feel lucky that I got enough measurements to find when the peak growth rate occurred. Regardless, I now see measurement of the trunk/branch thickening as a good experiment response, especially when the effects of pruning/defoliating are being examined. Weight gain effectively requires all pruning/defoliating to be synchronized with repotting which most often isn’t the best time for such treatments. This restriction isn’t present using stem-thickness.

On 4 Sep, I washed the Turface out of the roots of #2, #4, #6, and #8 and checked their weights. Because of the broken stem issues it isn’t possible to say much about weight gain, but #8 (that didn’t get broken) added 11 grams to its 3 gram starting weight. If this were the norm without stem breakage, almost a 4-fold increase in weight is impressive for one growing season. On the other hand, the original weights were taken without foliage. The foliage is likely a large part of the weight of a tree at this stage (#8 was the most heavily foliated tree repotted, shown at the extreme right of the collage below). But note that this is the only time this particular issue arises. In the future, spring repotting weights will be with bare trees and Aug/Sep repotting weights will be with foliated trees. This is the first Aug/Sep potting. Therefore these measurements are just fyi, on the road to getting annual data.

While there definitely was root growth this season, it was meager in my opinion. Consequently I only trimmed the tap roots a bit and kept the full length of the lateral roots, before putting them back into their respective pots on 4 Sep. It happened to be a relatively cool and overcast week, but #8 needed to be kept in the shade when the clouds parted and the air dried out a week later. All four repotted plants appeared to do fine though, as a group, they dropped leaves about one week ago, somewhat ahead of the other redbuds that are still hanging on to a few leaves.

Roots on #2, #4, #6, and #8 on 4 Sep

Redbuds # 2, #4, #6, and #8 on 21 Mar


Possibly you can see the gold paint marks near the root collars in this last collage. These are the points that I measured the base diameters on 21 Mar and were also accompanied by a black Sharpie mark. I could not find any of these on 4 Sep., so I made the measurements at my best guess of one centimeter above the root collar.

id	4-Sep-13 base (mm)	4-Sep-13 repot. wt (gm)
2	3.87?	5
4	4.76	4
6	5.23	6
8	5.46	14

 

[0soyoung]

Winter Cold?

By 17June 2014 it was clear that many of my Eastern redbuds had died. Of the 8 experiment seedlings, 5 were dead and 3 were alive. I am guessing that the reason is that I failed to adequately protect the roots from winter cold. I am surprised that a plant with ‘canadensis’ in it name would be not be cold hardy, if this indeed was the cause. I can only say that the experiment does NOT demonstrate Aug/Sep repotting was the cause of seedling deaths because essentially the same number died in each group:

• 2 of 4 trees potted only once, on 21 March 2013, died (#1 and #7)​

• 3 of 4 trees repotted on 4 September 2013, died (#2, #6, and #8)​

Again, the experiment also included potting half the seedlings in clear orchid pots of ProLeague instead of deeper black pots of MVP, and longitudinal cuts near the trunk base. The following table summarizes the 3 treatments, 4 potential interactions, and the alive/dead results. We simply count the number of ‘+’ and the number of ‘-‘ dead or alive to tally the response to the factor or interaction of factors listed at the top of each column (note that each has exactly 4 ‘-‘ and 4 ‘+’ seedlings; each ID represents a single seedling).

ID	@ 17 June 14	4 sep 13 repot	clear pot	cuts	repot & clear	repot & cuts	clear & cuts	repot & clear & cuts
1	dead	-	-	-	+	+	+	-
2	dead	+	-	-	-	-	+	+
3	alive	-	+	-	-	+	-	+
4	alive	+	+	-	+	-	-	-
5	alive	-	-	+	+	-	-	+
6	dead	+	-	+	-	+	-	-
7	dead	-	+	+	-	-	+	-
8	dead	+	+	+	+	+	+	+

The response to every factor and interaction is 2 or 3 dead in one group and 3 or 2, respectively in the other. It is intuitively obvious that this is just ‘a flip of the coin’. Therefore, the seedlings died because of some other cause(s). They did not die because of repotting in September. They did not die because of the trunk cuts. They did not die because of the media or pots in which they were planted. Something else caused the deaths.

Despite discussion about grouping and tracking of pot locations, I failed to record pot positions. I think the 4 that died sat on the periphery of a cluster of pots over the winter and that the 3 that survived were protected from cold were in the interior of the grouping of pots. Any of the 3 weeks with lows around 20F experienced in my neighborhood may have done them in.

week ending	ave F	low F
16-Nov-13	49.01658	42
23-Nov-13	40.50127	29
30-Nov-13	43.85632	36
7-Dec-13	33.28029	20
14-Dec-13	35.27039	19
21-Dec-13	40.59247	31
28-Dec-13	41.85108	35
4-Jan-14	41.92484	34
11-Jan-14	43.03955	32
18-Jan-14	44.43187	37
25-Jan-14	41.38426	36
8-Feb-14	30.81351	21
15-Feb-14	35.32619	32
22-Feb-14	40.52300	33
1-Mar-14	39.27760	32

This suggests that another experiment using a refrigerator/freezer might ‘prove this speculation, but I had other losses over the winter of 2013 that tend to support this idea. However, I think this would be a bit too much of an academic obsession. I am now just taking a little more care to protect my trees’ roots from cold over the winter.

To sum up:
• Repotting on 4 Sep 13 did NOT kill my cercis Canadensis
• Neither did the type/size of pot (black/clear) or medium (Turface MVP vs. finer ProLeague)
• Neither did the administration of longitudinal cuts at the trunk bases
• Some factor outside of the experiment did – I speculate it was temperatures dropping to near 20F or below, during the 2013-2014 winter.

 

[sorce]

To sum up:
• Repotting on 4 Sep 13 did NOT kill my cercis Canadensis
• Neither did the type/size of pot (black/clear) or medium (Turface MVP vs. finer ProLeague)
• Neither did the administration of longitudinal cuts at the trunk bases
• Some factor outside of the experiment did – I speculate it was temperatures dropping to near 20F or below, during the 2013-2014 winte

Without the trauma, I reckon they would've wintered fine, I think the cold was merely the straw cigarette in the Camel Pack, or however that goes!

The root condition is almost exactly that of the ones on Hagedorns blog against turface!

I'm inclined to think mixing America's favorite pastime with Japan's is a clear no no, leave the turface on the ball field!

It's almost like they put weed killer in it or something, it just doesn't work!

I fully appreciate the experiment, but it only seems to prove any turface is bad turface!

Sorce

 

[Gene Deci]

FWIW Six years ago (if I remember right) I started about a dozen red buds from seed. I gave three away and have six left which are still alive and well. Each has been treated exactly the same, due to the fact that they have been pretty much neglected since they were put in individual pots the second year. The variation in size of the trunk diameters is over double and variation in height is about one an a half. No two are the same. Six is not a large enough sample size to draw any conclusions, but it makes me wonder if size variation might be caused by individual plant genes as much as growing conditions.

Seeds were from a neighbor's tree by the way.

 

[0soyoung]

... Without the trauma, I reckon they would've wintered fine, ...

What/which trauma?

ID#1 had nothing done to it other than to pop it into a pot, yet it died.

 

[0soyoung]

Six is not a large enough sample size to draw any conclusions, ...

There were 8 trees in the experiment (probably just a typo).

This experiment was a bust. It was not conceived to have trees living/dying as the response. A statistically significant effect could only have been made if all four seedlings of one treatment level had died (e.g. all 4 fall repotted seedlings lived versus all of the spring died, for example). But, I still think it would have been possible measuring seasonal weight gains as the response to the treatments.

... but it makes me wonder if size variation might be caused by individual plant genes as much as growing conditions.

This is an interesting question, but in the context of this experiment, pix of all the trees taken on 4 Sep 13 were presented in post#7 of this thread. I don't see any apparent relationship of size or any other aspect of their appearances to which ones died and which ones didn't.

There will always be variations from unknown causes (genetic or otherwise). Experimentally, one can cope with this by comparing averages of groups. Experiments control factors to see if an effect can be 'turned on/off' so to speak. In other words, you could explore your interest by following the methodology I've outlined here. A key is to randomly assign trees to treatements, then the groupings will be equivalent, on average.

 

[Gene Deci]

There were 8 trees in the experiment (probably just a typo).

The six were the trees I still have alive, not yours.

There will always be variations from unknown causes (genetic or otherwise). Experimentally, one can cope with this by comparing averages of groups. Experiments control factors to see if an effect can be 'turned on/off' so to speak. In other words, you could explore your interest by following the methodology I've outlined here. A key is to randomly assign trees to treatements, then the groupings will be equivalent, on average.

In my professional work, averages require hundreds of data points to be statistically significant. Thousands are better. Any useful statistic does. Although the affect of genetics on tree growth might be interesting, I really don't have the time or resources to do an experiment that would be meaningful.

 

[Leo in N E Illinois]

Given the native range for C. canadensis extends into Canada, to near Hudson Bay, this species is very cold tolerant. Your assertion that cold temperatures killed the seedlings is likely incorrect. Though the observation that the ones wintered on the edge of your shelter were the ones that perished may point to exposure to wind & or dehydration caused by winter sun. Cold alone is not likely to kill a species that reproduces in nature as far north as the southern tip of Hudson Bay. The species is always listed as a forest edge species in its habitat preference. Key here is that there will be a plentiful leaf litter mulch every winter and some protection from winter sun as a result for seedlings.

I would suggest a re-run of the experiment using Turface vs Perlite or Punice as a treatment. As others pointed out, I am of the belief that Turface is not a good growing medium for any species that prefers a slightly acidic soil. Even the manufacturer's of Turface recommend that it not be used as more than 20% of a soil mixture. Even for sod. The manufacturer never intended that it be used as 100% of a growing medium. I used Turface for years, with disappointing results. I like the way Turface looks, feels and it appeals to my idea of what a bonsai soil should look like, but in actual use it is not good when used as more than 10 or 20% of a mixture. When I switched to other media I was surprised to see how much better my roots looked.

In my experience speceis of trees that are noted for thriving in high salt environments and or alkaline soils seem more able to grow reasonably well in turface. But many of our deciduous trees prefer a low salt, and slight to moderately acidic soil really seem to hate Turface. Of course my municipal water is moderately alkaline, with total alkalinity around 175 ppm as calcium carbonate. If your irrigation water is very soft with low alkalinity you may be able to counteract some of the negative effects of Turface.

I do applaud your willingness to do the actual work needed to answer questions. You set up a better experiment than I probably would have if left to my own devices. I would suggest more replication for each treatment configuration, 3 or more for each square of the grid. I also would have chosen different variables for the experiment - perhaps focusing on 2 types of media-pumice vs turface, and repotting timing. Or perhaps fertilizer as a treatment. Regardless, it is a nice try. I do think you are right that trunk caliper is a reasonable stand in for plant weight. And trunk caliper is a trait we are focused on in bonsai.

Thank you for doing this, it is thought provoking.

 

[0soyoung]

These seedlings were freebies thrown in as part of an ArborDay membership and it is only because of this that I used them for an experiment focussed on repotting time. While they do have some interesting characteristics (such as their leaf buds), I don't find them to be an interesting subject for a bonsai-oriented study and will not be doing anything further with this particular experiment.

I have been very pleased with Turface. I get great root growth with deciduous trees such as the attached example of Amur maple roots grown in a cubic ceramic pot. Michael Hagedorn's problem with Turface turning into concrete was because he uses poo-balls/cake fertilizer - the moral is: don't put shit in Turface. The corrollary is that if one is convicted to the use of poo-balls, don't use Turface. I use Osmocote.

Turface assays to be slightly acidic. I grow many azaleas and rhododendrons in pure Turface and have yet to encounter any notable troubles - they thrive. I do not have hard water issues, however.

Nevertheless, I do think comparisons with pumice/scoria/lava type media would be very interesting were I to find a local source at reasonable cost.