Can Citrus grow in zone 6?

Update after a hard winter

Being located in USDA frost hardiness zone 6 (6a previously, 6b according to newer data), I grow most of my Citrus plants in pots and move them for the winter. I also try to grow some of the hardier ones in the ground. But can Citrus plants grow here reliably?

It’s time to publish an update on my inground citrus after the winter. Although the actual low was not the lowest – approx. -16/-17°C, the winter can be considered hard. The soil was frozen constantly for over a month, and in some days frost was combined with strong wind and/or sun. The perceived low temperature for my area was -23°C according to ICON model, or -25°C according to GFS (data from Ventusky).

The plants other than pure Poncirus were covered (or partially covered) with conifer twigs, oak leaves, peat, snow.

Early signs of damage

The first signs of damage were already visible during the winter. It became clear that this time also the hardiest Citrus resembling Poncirus: Kinga, the seedlings of citrandarin HRS899 O/Q (I will refer to it as “O/Q” for brevity) — will be damaged. The year before they were essentially damage free.

A correlation could be observed between the appearance of twigs and the degree of damage. The more vivid green and watery the twigs appeared, the more cracks they exhibited. Olive green twigs with dry appearance suggested no damage. You can see the difference in the following pictures:

May 2026 – more clarity

In May, most of the damage was already established. Pure Poncirus plants had very little to virtually no damage visible (not counting late-season growth which was killed), they were flushing and blooming.

In plants resembling Poncirus, the results varied. 2 on 5 O/Q seedlings showed signs of life above the level of winter protection — ‘D3’ with virtually no bark cracks and ‘C1’ with severe cracks, but still alive to the top and flushing. Kinga1 (grafted on Poncirus) died to the protection level.

More damage was visible on hardy hybrids. In this group, there was no survival above protection level, but some survival below it. I believe that the more hardy a plant is, the higher above ground it will survive. Yolar (Flying dragon x Yuzu) stayed alive to a higher level than O/Q hybrids ‘Sorfo’ and ‘Korela’, suggesting its better hardiness.

June 2026 – final results

Pure Poncirus plants are fine. Fruits set both on Flying dragon and the standard strain ‘Karel Mundl 1’.They are more chlorotic this year — difficult to tell if the hard winter could have contributed to it. Iron deficiency is a constant problem in my alcaline soil. Mulching with acid substrate, such as blueberry soil, should help as usual.

Out of the O/Q seedlings resembling Poncirus, ‘D3’ still seems to be the hardiest one. The stem is healthy with no cracks visible – even in parts which were exposed to frost, sun and wind. Only late-season growth was killed, similarly as in pure Poncirus plants. The second one — ‘C1’ — ultimately died above the level of winter protection and is regrowing from below. The other seedlings are also regrowing. There’s also a small piece of ‘C3’ surviving unprotected, grafted high on Poncirus.

Yolar (Flying dragon x Yuzu), and Orla (Flying dragon x ?) are regrowing. Yolar is partially monofoliate, up to 50% at this stage of development. Perhaps with age the leaves will become entirely single. Of those two, only Orla is twisted in Flying dragon style.

O/Q hybrids – Sorfo and Korela are regrowing. Sorfo survived a bit higher than Korela, again indicating a slightly higher level of hardiness. But both are worthwhile given that they have survived their fourth winter in the ground. (Last year I lost two other prospective inground hybrids of O/Q growing in the ground — Lotka and Mazurek — while those two survived.)

Mutivariety plant (the rootstock is Flying dragon) exhibits various results. Citrandarin Schleipfer seems the hardiest one – apparently the Changsha parentage helps it. It took some damage, but only a bit more than Kinga1 – and it looks much more Citrus-like than Kinga. I find it a very prospective variety for further tests.
Citrandarin Forner-Alcaide 5 seems less hardy than Schleipfer, but survived as well and is regrowing. Note the light color of the new leaves – it always looks like that.
Yuzu ‘N4’ and ‘Cologne small leaf’ grafts died completely. Too bad, last year they survived under protection.

After this winter, I think the only 0% Poncirus plant that can thrive here is Ichang papeda. The plant was protected with a big mound, and additionally, a big garden bag with organic matter was placed next to it. It survived close to the ground, and even a few old leaves stayed on the plant. Now it’s regrowing strongly. The rootstock is Poncirus, and the graft level is very close to the ground, which seems to help.

As for other inground plants, I’m suprised comparing two Kinga3 seedlings which survived below the protection level with a seedling of Poncirus#7, which is severely damaged. Maybe the protection was too weak, but still I thought it was hardier. Prores4 (limequat x procimequat or limequat x hindsii; it was in greenhouse, not in open field) died. It could be expected knowing its limequat parentage, but having survived the last winter with a low of -13°C gave some hope.

Brief results

Below you can find the ranking of survival, arranged in order from the best performers to the least hardy varieties. I marked in bold the plants which survived also above the protection level. The crossed-out varieties are the ones which died.

This winter was a good opportunity for selecting the hardiest varieties. Out of the Poncirus-like plants, I find the O/Q seedling ‘D3’ the most promising. Hopefully the fruit will be at least of the same quality as the mother variety HRS899O/Q, while the frost hardiness is probably higher.
Of the hybrid varieties, citrandarin Schleipfer made a good result again, and even though I don’t know its fruit quality yet, I find it a very prospective variety.

Growing Citrus in zone 6 – prospects

As for the question “Can Citrus grow in zone 6?”, the answer is: yes, but only the most resistant ones will survive long-term without artificial protection. This narrows the scope to Poncirus and the hardiest Poncirus-like varieties, and limits fruit quality.

Another option could be to look for moderately hardy plants that can reliably regrow and bear usable fruit even after frost damage. This approach would probably need special cultivation methods, and special varieties able to fruit under such culture.

In each case, breeding work is needed and the progress is likely to be achieved in small steps — but the potential outcome is promising.