Cold-hardy Citrus test - Winter 2020
Jan 3, 2022 7:05:34 GMT -5
mikkel, Florian, and 4 more like this
Post by jibro on Jan 3, 2022 7:05:34 GMT -5
Last year I tested Citrumelo Swingle grafted low on trifoliate rootstock, Citrumelo scion was taken from juvenile Citrumelo seedling purchased from Adavo nursery.
In this gallery you can see the damage, most of the leaves were destroyed, but some survived, 1 to 2-year-old tree shoots were also damaged, the biggest damage was due to the late April frost on the Trifoliate rootstock where were several bark cracks.
Higher-resolution pictures in my article
Citrus limetta Patriarcha - a very small seedling did not survive, it confirmed that for non-cold hardy citrus varieties this protection is still inadequate even in a relatively mild winter.
I am testing these survivals and some new varieties in the same greenhouse during this winter but without a frost blanket, so they will be exposed to lower temperatures, the difference between the temperature outside and under frost blanket is about 6 °C, so this frost blanket is surprisingly effective at least for small seedlings.
I do want to graft all of my hardy citruses on small Poncirus rootstocks and test them in this condition, my goal is to make a direct comparison between these varieties in a small area with the same condition as possible: same rootstock, no different wind or sun exposure, no plants weakened from fruit crop, at a different age, etc.
Tested plant was whole winter outside in old damaged greenhouse without south wall and part of the roof, only protection was from snow and rain, temperature and wind exposure was the same as outside.
I live in central Europe, our zone is comparable with USDA 6A, last winter was unusually mild, minimum temperature was two nights with - 14°C (6,8 F), the rest of the winter and spring days were mostly temperatures down "only" to -10°C (14F). The graph uses measurements from a probe about 25 km away, in my location the temperatures were ~2°C higher.
In this gallery you can see the damage, most of the leaves were destroyed, but some survived, 1 to 2-year-old tree shoots were also damaged, the biggest damage was due to the late April frost on the Trifoliate rootstock where were several bark cracks.
Higher-resolution pictures in my article
Citrumelo survived and has new growth but I will not repeat this trial because these F1 Poncirus hybrids are apparently not hardy enough even for a very mild winter in my location and I don't see any reason to grow them outside without protection...
I made also another test inside my unheated greenhouse sheeted with only 4mm thick polycarbonate and seedlings were covered with a frost blanket.
I tested several small mostly stunned dwarf seedlings, probably zygotic from Citrumelo 5 Star and N1 Tri Voss, also one Juanita mandarine, SP Urban F2 (Ichang papeda x Otaheite Rangpur), Clem-Yuz 2-2, Yuzu - more likely Yuzu hybrid (seeds from USA), defoliated in autumn before this test.
In the greenhouse under frost blanket was minimum temperature during winter 2020 - 8°C (17,6 F) for two nights and only few nights with -6°C (21,2 F), the result:
1. No damage
Ventura Lemandarin - no visible damage, the plant grew normally during the following season, very promising variety for my conditions.
Ventura Lemandarin - no visible damage, the plant grew normally during the following season, very promising variety for my conditions.
SP Urban F2 - no visible damage, but the plant did not grow much this year, it sprouted a bit later, -8°C is no big problem for SP Urban, it can probably tolerate a few degrees lower temperatures.
2. Minor damage
Yuzu (USA) - the tested seedling lost almost all its leaves in autumn, maybe due to over-drying, so I could not monitor the condition of the leaves during the winter, 2 immature shoots died, but the plant grew normally this season.
2. Minor damage
Yuzu (USA) - the tested seedling lost almost all its leaves in autumn, maybe due to over-drying, so I could not monitor the condition of the leaves during the winter, 2 immature shoots died, but the plant grew normally this season.
Citrumelo 5* - about 3 - 4 of the weakest seedlings did not survive, but most of the plants in the planter survived without damage.
N1 Tri Voss - about 3-4 of the weakest seedlings did not survive, but most of the plants survived without damage, they are dwarf plants with weak roots, so no major growth this season.
3. Minor damage + slow growth
Clem-Yuz 2-2 - after the end of winter the plant did not show significant damage except for a few leaves, but this season it practically did not grow, but this is quite normal for Clem-Yuz seedlings in my conditions, these grow poorly on their own roots.
4. Dead
Juanita- the plant lost all its leaves and shoots and there was total dieback, confirming my doubts about any major hardiness of this variety and I'm not sure if it is at least as hardy as Satsuma.3. Minor damage + slow growth
Clem-Yuz 2-2 - after the end of winter the plant did not show significant damage except for a few leaves, but this season it practically did not grow, but this is quite normal for Clem-Yuz seedlings in my conditions, these grow poorly on their own roots.
4. Dead
Citrus limetta Patriarcha - a very small seedling did not survive, it confirmed that for non-cold hardy citrus varieties this protection is still inadequate even in a relatively mild winter.
I do want to graft all of my hardy citruses on small Poncirus rootstocks and test them in this condition, my goal is to make a direct comparison between these varieties in a small area with the same condition as possible: same rootstock, no different wind or sun exposure, no plants weakened from fruit crop, at a different age, etc.
