Botanical properties of a Cold Hardy fig tree

[smithmal]

Please excuse me if this has been covered before. I did a limited search and didn't get any hits.

Categorizing fig varieties according to their "cold hardiness" depend on the presence of many ecological elements to increase their cold hardiness including:

1. Age of Tree
2. Caliper of Trunk
3. Soil moisture
4. Soil conditions
5. Planting depth
6. Environmental Landscape (i.e. how well sheltered is it from winds, etc.)
7. Ambient Temperature fluctuations (i.e. reduction of warm ups followed by cold snaps)

But, if you had two fig trees that were identical in all aspects except for their genetic variety, what botanical properties would make Fig type "A" more hardy than Fig type "B"? Are their cell walls different in some way, do they store sugars differently, have deeper or stronger roots or have differences in xylem/phloem transport?

I put out my lettuces out a couple weeks back which are considered cold weather crops. I've read that lettuces protect themselves from frost/freezes by moving the water out of their leaf cells when it gets below freezing to reduce cellular freeze damage and then re-hydrate their leaves when it warms up. For this reason, you never want to pick lettuce in the early morning when its below freezing as the lettuce leaves are less hydrated.

This got me thinking about figs and what mechanisms they do to deal with cold weather. Any and all information is appreciated.

[SarinaP]

I found the forums after a few years of thoroughly abusing my Monticello Marseilles, but here goes:
1. 4 years old
2. multi-trunk (3), approximately 3/4" thick
3. Regular 7a weather patterns, I don't water it regularly
4. Heavy clay soil, was planted with 1:1 potting soil and compost
5. Root ball flush with the ground
6. Out in the open in a mulched bed on my front lawn
7. Typical 7a stuff, like what you're seeing in MD, I'm sure

Year 1, I kept it in a pot. I received it as a single-trunk 3' tree. Year 2 I planted it in ground and it died back that winter. Year 3 I found the forums and cut it back to 4' tall with 3 main trunks, covered it, and have seen no dieback at all. This is its 4th year with me.

[smithmal]

SarinaP,

Thanks for responding, but what I was really after was botanical information of fig trees in general that allow certain varieties to handle or survive cold weather conditions better than others. I know we have some people on the board that are very knowledgeable in the areas of genetics, botany and/or plant physiology.

[SarinaP]

Ohhhhh... gotcha. Smart people stuff.

[Pino]

Malcolm,
I think you nailed many of the environmental factors that affect survival of figs in cold weather.

Other factors include the overall health of the fig plant, exposure to wind chill, duration of the cold temperatures, acclimatization of the fig to the cold i.e. the cold came as gradual onset rather than sudden temp drop so the fig had time to adjust).

Agree with you, (don't know how or why) but there seems to be botanical differences since some fig varieties seem to break dormancy much faster than other figs and some figs take longer to go dormant.

Bottom line is that any fig green growth will not survive a hard freeze. Dormant and hardened fig branches CAN survive to -9C (15F) and push out new growth although it appears the breba and primary buds are destroyed at these temperatures so you need to wait for the secondary buds to push out.

[Rewton]

It's a great question. Have you tried doing a search in the primary scientific literature? I seem to remember some discussions on figs4fun in which it was asserted that the antifreeze properties of the sap vary between varieties. In other words, whatever substance in the sap that caused it to resist freezing was higher in some varieties than others. I don't know if there is any scientific basis for this. Differences in cold-hardiness between varieties probably also reflects a tendency to go into deep dormancy once the weather gets cool in the Fall and to stay there even when there are brief warm spells in late winter.

[Rewton]

This review has a lot of good information pertinent to your question:

Sanghera et al. "Engineering Cold Stress Tolerance in Crop Plants", Current Genomics (2011) 12, 30-43.

[smithmal]

Thanks Rewton, I'll check it out.

[smithmal]

Here's an article that might shed some light on the subject.

The author suggests that chilling (damage above 0C) and freezing (damage below 0C) injury occurs due to intra- or extra-cellular freezing (frost damage) rather than exposure to cold temperatures over an extended period of time. Plants can decrease this injury by increasing the solute concentration within the cells (like adding salt to water). Studies have indicated that the rate of cooling rather than the temperature is the main cause of cell injury/damage.

Other studies suggest the rate of thawing of the plant may also play a part with cell damage. If a plant thaws too quickly the rate of rehydration within the plant cell occurs too quickly and the plant's cells sustain damage. The paper indicates that many citrus growers will turn on fans in their greenhouses in the morning after a particularly cold night to slow the thaw rate.

Basically there's three mechanisms a plant can provide to protect itself from frost damage:

1. Avoidance - creating a microclimate around itself to reduce frost damage (large canopy, snow retention, bulky organs (trunks or fruit) that slow the rate of cooling or thaw
2. Tolerance - cellular mechanisms to reduce the rate of cooling and ice formation intra and extracellularly (increase in cellular sugar or lipids to decrease freezing point or stabilize the cell wall)
3. Hardening - a combination of avoidance and tolerance mechanisms that a plant will do to rapidly go into dormancy and/or slow the thaw rate

Bringing this full circle, as fig growers we spend a lot energy trying to help out with mechanism #1 (winter protection). Picking "cold hardy" fig varieties may help us out with issue #2 (tolerance) and container growing figs and moving them into a sheltered space artificially allows us to control the ambient temperature and stabilize the rate of hardening off (issue #3).

I'd be willing to bet though, by doing the winter protection, we are also providing the fig trees with more time to successfully harden off by reducing rate of cooling and/warm when snaps occur in the late winter or late spring. By providing the fig with more time to successfully go dormant or successfully thaw out less cell damage occurs. This also means that if you start your winter protection too late (and your fig deals with rapid freezing) or remove it to soon (your plant deals with rapid thawing) frost damage can occur.

Picking "cold hardy" varieties would suggest two things:
1. The fig variety has a faster hardening off process and does so at higher temperatures so that they are fully dormant by the time the really cold weather hits which reduces cellular frost damage
2. The fig variety is more successful at transporting cellular sugars and lipids to increase the solute concentration which would in turn decrease the cell's freezing point and reduce the amount of damage from rapid cooling or thawing.

So, what I took from this is the following:

1. When first planting your fig trees bury them deep to better insulate the roots
2. Start your winter protection early to protect against a sudden snap freeze that occurs in the fall and early winter
3. Keep your winter protection on longer to protect the fig from rapid thawing during the late winter/ early spring period
4. Pick varieties that go into dormancy faster or do so at higher temperatures

Too bad we can't pump our fig trees full of automotive coolant before winter hits....

[AscPete]

Strictly speaking there are no "Cold Hardy" fig cultivars... Ficus carica is native to a dry temperate zone 9 -10 and cultivating figs in colder zones require the listed cultural practices. Most fig cultivars will have major die back of 1 year old and younger wood if exposed to temperatures below ~20 deg F. (usually noted as 15 deg F).

There are however some healthier and or hardier varieties (cultivars) which perform better when exposed to cold weather. Some of these cultivars (1) ripen their figs earlier in the season and (2) lignify young green branches quicker. Like many plants figs seem to be able to acclimate themselves to their environment, but they will not survive outside of their zone without some winter protection and or cultural practices / planning.

The cultivar Florea is claimed to have a smaller diameter pith cross sections compared to other cultivars, but its only anecdotal.

Looking forward to any additional info on this topic.

[jrdewhirst]

Smithmal -- Good stuff. Thanks.

[GregMartin]

So, of the varieties that perform better when exposed to the cold, what genetically related groups do they fall under...i.e. EBT group, Mt. Etna group, etc.

Asking because if the groups have differing genetic adaptations then efforts to cross between these groups may perhaps provide significantly better cold weather performance in the resulting offspring....very interested in seeing what would result.

Does anyone have a list of the hardier varieties grouped by relationship they can share?

[GregMartin]

Thanks Pete, I've been hunting around for a good fig dendrogram but so far haven't found one. That analysis has been done though, right?

[AscPete]

The only one I know of is the UC Davis DNA mapping which is incomplete and inconclusive.

http://figs4fun.com/Links/FigLink1110.pdf

[GregMartin]

Thank you Pete.

[mountainfigs]

Great research and analysis, which shows why planting figs near heat sinks and protective barriers like boulders and stone walls and earthen berms, and on the north side of such structures, can be effective.

[AscPete]

An observed "Botanical" property that has not been mentioned, and may not have anything to do with "Cold Hardiness" is the ability of a cultivar to ripen figs when the average daily temperatures are below 70 deg F. Many cultivars will only ripen their figs properly when the average daily temperatures are above 75 Deg F.

Champagne is one such cultivar, it ripens figs to a jammy interior even in cooler weather.

[smithmal]

I got thinking about this b/c of the recent thread on Nero 600M. There has been several reports that Nero 600M suffers significant freeze damage by some owners even though it's categorized by many as a "cold hardy" variety.

When looking up information on Nero 600M it was noted to be discovered on an Italian mountainside about 555 meters above sea level. At that altitude, it was noted that each year following cold winters, the variety suffered little damage and would produce figs each summer (unfortunately @ 555 meters the summers were very short so rarely did this variety produce ripened figs).

Frost damage experiences with US growers indicate otherwise. So why is that?

My assumption is that when Nero 600M is in its native environment the fall season cool down into winter is much more gradual than what occurs here in some parts of the US. Because of this, the variety has more time to go completely dormant before the really harsh winter temperatures show up thus allowing the tree to have an easier time acclimating to winter temps. I'd also be willing to bet that on that Italian mountainside, the increase in temperature in the springtime is also gradual without dramatic warm ups and then cold snaps.

Pete indicated with his espalier setup, he waits until mid-May before taking away his winter protection and b/c of this he protects the laterals and scaffolds from unnecessary thaw stress during the spring time period as they are buried under 6" -12" of pine shavings.

I'm a gardener and I know loads of gardeners that will try and play the odds with mother nature and transplant their veggies early when they see a springtime warm up. You'll also see loads of veggies show up in March, April in the big box stores. In MD, our transplant date is Mother's Day (when 90% of frost warnings for our area have expired). Putting out veggies earlier than May 15th is a risk. Some years you can get an extra month of growing, some years your plants get killed or really stressed from snap colds.

I'm betting removing your winter protection or doing the "fig shuffle" is the same way. You can put it out early and try and get some additional days/weeks of growth out of your figs, but you'd better keep your eye on the nighttime temps as a cold snap would really do some significant damage...

[AscPete]

Whats missing in lots of the "Cold Hardy" anecdotal reports are actual temperatures experienced by the exposed branches. The mother La Radek BT is also another reputed cold hardy fig cultivar that actually has major die back when the temperatures are in the teens although is grown against an exterior wall.

http://www.ourfigs.com/forum/figs-home/3084-let-s-talk-english-brown-turkey

[adler]

Hardyness in zone 6 may be a moot issue. The polar vortex 2013 gave us -10 deg. 2014 -5 deg, I don't believe that any outside fig would survive above the ground. I have cuttings from a local fig that had a trunk diameter of 11" at 18" above the ground. It was supposedly extremely prolific, age unknown. Both vortexs killed everything above ground . I now pot and protect the figs and try to aquire figs that set fruit in our summers.
Bill E . Md

[drew51]

I agree Bill, I'm in zone 6 and last year we got down to -16. Crazy, we are really zone 5. I think if you buried the tree it would be OK, otherwise stick to containers.

[smithmal]

I'm in zone 6B my falls and springs are just too variable (cold/warm snaps) to expect good fig hardiness year in and year out. That being said the measure of protection that the step over espalier technique provides is very attractive. I was thinking of espaliering six cold hardy fig varieties on a step over support and burying the laterals and scaffolds each winter in 12" of pine/bark (similar to AscPete). Anything else that I REALLY WANT would be container grown (maybe another 4-6).

[drew51]

It certainly is worth experimenting. One has micro climates etc., and your plan sounds very reasonable smithmal.