To protect or not to protect

[gordonh1]

I'm starting to grow cold-hardy citrus and thinking about strategies. I'm east of Seattle with mostly mild zone 8 winters but the rare cold weather event down to high single-digits F (- 15 C) occurring about once per decade.

I want to grow hardy fruits that have good uses and I'm considering a breeding program, but for now just focusing on growing strategies for the plants in my collection. I'm an addictive plant collector and have directed this focus to cold hardy citrus, starting this year, so I admittedly have maybe gone a bit too far too fast, and acquired plants that now may be quite a big project to grow properly, so I need to get educated fast and know what issues I need to deal with, especially before the coming winter.  I have just recently read this forum all the way back to the beginning, so I'm trying to distill the diverse advice down to what will help me.

I am relying on having the greenhouse, which is currently being built, but the plan is to have a place to keep immature plants and overwinter Citrus in containers with the thermostat set to somewhere around 50 F (10 C). I have read about the "rule of thumb", to wait until trees have a trunk as thick as a thumb before planting outdoors. Before that time, they can enjoy greenhouse living.

I have a Flying Dragon and a "regular" Poncirus, no real worries with them surviving outdoors but I have to see that confirmed since this is my first year with them.

I think I can grow some Poncirus hybrids outdoors without protection. I have Dunstan, Rusk citrange, Swingle, and C-35.  But I did notice some cold damage (leaf whitening) on the youngest C-35 and Swingle seedling plants even in April here.

I think Yuzu is worth trying outdoors, and I'm planning to try it both on its own roots and on Flying Dragon rootstock. That way, I can get the effect of the FD rootstock on improved cold hardiness, and also I can have a Yuzu that might come back from its own roots if it gets top-killed in one of the rare cold events.

I will try Changsha outdoors, and maybe Keraji.  I have a US 119 on order, but I learned about the fruit splitting problems in rainy weather, which we definitely get, so that one might have been a poor choice. But maybe I can grow it in a container and move it to the greenhouse where it won't get deluged with rains.

Nansho daidai (taiwanica), Ichang lemon, Thomasville citrangequat, and Ichang papeda are here now, and seem like possibilities to try outdoors. I'm not sure Ichang papeda is a sensible species to grow as it's maybe not edible, but anyway I have acquired the plant, so now I will try to keep it alive and if I do breeding, it would certainly be interesting to use. I did read that it might not be as hardy as some have claimed.

Where it gets tricky is when growing the even less hardy types, where I don't have high confidence they would overwinter outdoors without protection, but maybe they could be grown with appropriate protection. I have quite a few in this category: Sudachi, Bloomsweet, Kishu, China S-9, Seville orange, Calamondin, various kumquats. I'd grow these in containers so I can overwinter them in the greenhouse, I think, but some like Bloomsweet might get too big and then what.  I guess when they get big, they can go outside and we will just see what happens. Also, I can graft Bloomsweet on Flying Dragon and keep it smaller maybe.

But once I'm growing the marginal varieties outdoors, that is where the protection racket comes into play. I don't want to sign myself up to be a slave to my Citrus trees, having to rush around in the middle of winter and wrap up my trees. But maybe it's not too much of a burden for a small number of trees once or twice a winter, only when temps are predicted to go lower than 15 F (-10 C or so)? I guess the Christmas lights could be strung up ahead of time and left on the trees permanently. What concerns me is that I've read about how others have worked very hard protecting their trees for many years, only to have the rare cold event come and kill them, making the whole effort futile without significant reward. I don't want to get discouraged.

Anyway, I'm attracted to the idea of growing and developing varieties of hardy citrus that don't need protection, but in the meantime exploring what's possible with varieties available now and developing the breeding stock I'd need if I am to embark on a more serious breeding effort. I have already started germinating some Citrus from seed. Well, actually as a child back in the 1970s, I planted grapefruit and lemon seeds from store-bought fruit in ordinary dirt we scooped up and put in a sawed-off plastic milk jug. Those seeds germinated and survived for 30 years in my parents' house in Alaska. I think they even bloomed, but that was after I left home.  But now I'm returning to this childhood dream. I already have some Yuzu and Flying Dragon seedlings that have germinated and are growing under a fluorescent light setup indoors for now. I can scale that up and grow hundreds of seedlings if I decide to dedicate the space to it.  And I have some amount of outdoor space where some trees could be trialed and grow if they can. Of course, the hope is to improve the fruit quality of the types that can grow outdoors unprotected in my climate.

I feel like this could be a tragically disappointing (and probably expensive) failure, or it could be something really exciting and rewarding. I guess we'll see.

[poncirsguy]

The fruits have to ripen before first hard frost regardless of the tree's capability.

[hardyvermont]

Citrus can be covered with a tarp for the winter and left that way for months without damage.  They don't have to be repeatedly covered and uncovered.  This has been discussed here and in the older forum a few times. 
However, if there is a heavy snow on the tarp it can can break the underlying branches unless there is some additional support.

A tree in Massachusetts kept under a tarp and warmed with aquarium heater in a water barrel kept fruit that were found to be
edible when uncovered in the spring.

[gordonh1]

OK, I was indeed surprised to read on the forum that Citrus don't really need light during the winter months when they're dormant, as long as they remain cool and don't get heated to trigger coming out of dormancy, right? You could put them in a cool garage without a lot of light or under the tarp.

But would there be a benefit to keeping them uncovered and able to photosynthesize as long as temperatures were mild, as they usually are in a maritime climate, let's say in the range of 25 to 50 F which is the typical range. It could even be above freezing for weeks at a time.  Would this be a benefit or would it tend to stimulate growth too much and break dormancy?  I would guess not so much unless it was also warmer.

I also read one has to be careful about creating greenhouse conditions where the heat generated by the covering does cause dormancy to break.  That's one of the reasons I was thinking about covering only when it was actually necessary. But as poncirusguy noted, yes the fruit has to be able to ripen, so either the outdoor varieties are only the ones that ripen before the colder weather arrives, or one covers them to allow the ripening to continue.  I gather that Thomasville is one that ripens later. I did try to choose ones that would ripen sooner but obviously not all do.

[hardyvermont]

"But would there be a benefit to keeping them uncovered and able to photosynthesize as long as temperatures were mild, as they usually are in a maritime climate, let's say in the range of 25 to 50 F which is the typical range. It could even be above freezing for weeks at a time."

That is frequently the weather in Zone 8a.  My observation is that if there is a benefit from uncovering and recovering it is minimal and given the amount of work required, not worth it.


Fruit of Owari from late blooms were edible when the tree was uncovered in the spring.  I don't know how edible it was but if a plant is dormant, wouldn't the fruit be dormant, and then ripen when warmth and light returns. 

[drymifolia]

Gordon, I hope you'll create a thread to document your success! I'm in Seattle and always happy to swap citrus cuttings or plants with other people in the area. My own collection is also relatively new, and not particularly extensive, but I just potted up a bunch of rooted Sudachi cuttings and probably will be giving most of them away to neighbors. I'll be planting one out this week and keeping one in a pot as backup for next year.

And if you are interested in trying an avocado in that greenhouse, I am always looking for people to join our cold-hardy avocado breeding effort. I think it's probably too cold in your location for growing them outdoors, though. But if you would agree to give some portion of the seeds or seedlings back to the project to be distributed to members, I could probably push you to the front of the line for a multi-graft tree for your greenhouse.

[gordonh1]

I sent a PM. Gardeners and plant lovers are often such kind and generous people, thank you.

Regarding Sudachi, there's one that we'd pick green before frost, so that seems like a good one for my area.  And mine is on Flying Dragon rootstock so I guess it would stay small enough to be able to protect fairly easily. I've seen YouTube videos where a hardy citrus grower wasn't able to get his trees covered completely after they outgrew the coverings.  The one in my collection that grows very large is Bloomsweet. I've read 25' according to Madison's web site. That's too big to cover, so that's why I was thinking maybe it needs to be grafted to Flying Dragon so I can manage its size. It's obviously too big to cover, I guess it's too big for the greenhouse, and too big for container culture. I think eventually I'm just going to plant it out as a larger tree and see what happens, but I'll keep a grafted version that I can manage better.

The Satsumas are said to grow up to 8 to 15 feet depending on the rootstock, which sounds a bit more manageable.

I'm growing some Flying Dragon seedlings, so I'll be able to graft and could then accept scions from other collectors. How long does it take for Flying Dragon to grow to grafting size?  I've grafted a few apples, but never Citrus, but I guess the principles are pretty similar.

[tedburn]

I tested grafting already with a few month old seedlings and you have to take care due to the size, but it works well, only the scions also have been seedlings.
But with normal scions not so big you already could graft on one or two year old seedlings.