Meyers are among the most cold hardy of the citrus; planted in ground, they can support cold down to 28F. In containers higher temps can damage, especially if the containers are elevated or sitting on a cold surface such as concrete or metal.
Most important, because of the sensitivity of the Meyer to light changes, you will want to start adjusting the plant by putting it in partial shade for 2 weeks; then to full shade for 2 weeks before putting them into the greenhouse. Hard as it may be to believe, inside in a sunny window... or in your case a plastic house, is almost the same light as full shade outside.

John gave you some good advice. I would start being concerned when temps start to hit the low 40's, especially if you do not have a thermometer or weather station near your trees (and are relying on the TV or newspaper's weather report). Christmas tree lights are good, as long as they are the old-fashioned kind, and not LED, and LED doesn't emit much heat at all. So, they need to be incandescent bulbs, mini or larger.

Patty S.

Thank you to all, our low temps average 38-40 during the coldest month of the year, with one week, maybe two of "just below" freezing. Now that's just for a few hrs a day during the early morning, during the day we pick right back up into the 50's-60's. So I should be ok with a mini greenhouse I suppose.

Should I consider taking any measures to keep roots/pots warm? Perhaps wrap a blanket around pots during the coldest of nights?

Thanks

If you put your pots on a piece of wood, the roots should stay about the same temperature as the air; and that is okay.

I garden in Santa Rosa, just north of RP (saw your water report). I have a Meyer lemon that has been in the ground for about 20 years. I have never given it protection, and we've gotten down to 20 F. We do lose lemons in a bad winter, but the tree is fine. Our neighbor covers hers with sheets and strings christmas lights under the cover. Her tree came out of this winter with 90% of its lemons. I figure the amount our tree keeps is the amount our family can actually use, because they produce so much.
For a new tree, I would protect it when it's freezing. Don't leave the cover on! I saw a poor lemon wrapped in plastic and left that way. It survived the frost only to die from being covered for too long.
Citrus is surprisingly hardy if it is healthy, just get it through the first few winters.
If you can move your pots under an eave that would be ideal.

Everyone always means well and very kind to help, but many miss the point that people are asking cold questions for 'potted' plants..Much different than ones in teh ground and much more dangerous to leave them exposed to cold temps as she described..)

In 'Containers;....30's will kill your trees in a short time, 40's will stunt growth or completley cause decline over time, below 55 with stall growth, and above 55 will encourage growth..

Take your pick..)

MIke

This post was edited by meyermike_1micha on Tue, Oct 7, 14 at 13:52

Thank you to all for taking the time help. Mike, would you suggest abandoning the "mini greenhouse" idea and putting them inside of a south facing window? My home stays in the 70's all winter. Not sure if that would be good or bad. If so, it seems as if you would suggest transitioning them now versus waiting for colder temps as I have already been seeing 50 deg temps at night.

I've had citrus in pots with 34F nights all winter long and no damage. That's in a greenhouse with very good thermostat and heater. So I know it's in the 30s most nights all night for 3 months. That alone won't hurt or kill citrus. If they die it's something else.

I'd also dispute the idea that a greenhouse is a low light environment. Mine certainly isn't. Shade outside is usually well less than 1,000 foot candles. My greenhouse is 5-6,000 midday. Outside in sun midday is 10-12,000 fc so my greenhouse is half that but everything grows great and light quality is very high. Under my woven poly the light is highly diffused meaning it comes from all directions and illuminates the lower leaves better than outdoors.

A greenhouse with less light than outside shade would have a very opaque covering. It won't be a greenhouse it would be a shade structure.

The key for citrus is keeping temperature, light, and water in balance. This is much harder to do indoors than in a good greenhouse. Indoors the light is usually too low.

Stick, I would never abandon any greenhouse structure of anything that will allow you to grow your citrus outside instead of inside..As it was said, there is much more light out there than indoors..

The temps I am much more concerned about because I live much further north of you just noticing your area and my nights can stay too cold for hours longer after yours..

Are your very cold nights short lived? I know that a few here have had experience with shorter cold nights on their plants than I have..I would listen to them..My wether, cold and sun angle are far less superior than yours and a whole different ball park.

What every you decide to do, good luck with them. You will know what works by the way your trees react.

Fruitnut made a very good last point and along with that your container growing mix will make a huge difference..

MIke

This post was edited by meyermike_1micha on Wed, Oct 8, 14 at 9:34

Mike makes a good point in that days in my greenhouse may be warmer on average than they would be in his environment. Mine are 30s night 50s day and 40s average. This is very similar to commercial citrus areas of CA with thousands of acres of citrus. I don't know what would happen colder. But don't they grow citrus successfully in pit greenhouses in Russia that are covered with snow much of the winter?

It also depends on whether you want growth in winter or wish to concentrate on fruit production. I'm after fruit and don't need any growth for months in winter. For that my environment works great. If you are an ornamental grower and want growth all winter then you'll need a warmer winter. But that is a difficult proposition indoors or greenhouse up north.

I was hoping for winter growth this year as I am not allowing any lemons to sit on tree's. I have removed them all in hopes of more growth.

This post was edited by StickString on Wed, Oct 8, 14 at 13:37

Stick:

Your top post says you are in northern CA. You have a good climate for citrus if you can just protect the trees from temperatures below about 28F. In your climate citrus trees don't grow in winter. They need to stop growth and harden off so as to avoid severe damage on those few nights when it drops below 28F, depending on where exactly you live.

If you insist on pushing the trees into growing in winter then you will need to avoid any temperature below 32F. That is easily done in a good brightly lit greenhouse with a good heater and control system. If you try to do it inside it could back fire and defoliate your trees.

It depends on where you are exactly. Some places in the bay area are nearly frost free. Most of the northern half of the state above 500ft are freeze prone.

I live in sonoma county. It does drop around the 30 degree range in the early mornings for a few hours before the sun warms everything back up. And that is not a nightly occurrence, just for a few weeks.

I would rather avoid heaters and such inside of a greenhouse. So I am assuming my best option is to avoid chasing winter growth and just attempt to keep them as healthy as possible all winter

I bring in my trees when is see low 40s steady that's end of October or early November for me.
Trace

Citrus are grown all over Sonoma county, mostly in the ground with very little frost damage. Some years the frost will last for more hours at a time than usual and cause minor frost burn. If you have only minimal cover, frost damage can be avoided. Al

Calistoga,
Thank you for the advice. Being that the pots are so small, I fear the roots will become too cold and cause damage. When you say minimal cover, can you give me an example?
Thank you very much

This is my thought..... I would purchase one of these cheap mini pop up greenhouses, place my two larger air layered meyer lemons inside, wrap them in old fashion x-mas lights and turn the lights on when I go to bed whenever the temps are supposed to drop below 45-50 degrees......

Thoughts? Will this idea keep my trees happy until spring?
Thank you

Sounds like way too much. My in-ground mature trees have had only fruit damaged even the year my swimming pool froze completely over. That was a 10 day period where the high never hit 50 and the low was below 32 every night.

My potted trees had no damage but I did move them into a protected location. With a predicted low of 26, I put some in the deep entryway to my front door with two 100 watt flood lights shining into a 10x30' area. I put the rest into my back patio near a 12' single pane sliding glass door and put one 100w flood shining on them from the other side.

Just make sure that any cold air can flow downhill away from your trees. The coldest spots will be where cold air can't flow away.

Your solution sounds like too much. That much protection is fine but that many lights sounds like protection from temperatures in the single digits. I'd be very careful putting more than 4 old-style Christmas lights in a plastic greenhouse that size. I wouldn't even turn them on until it was predicted to be 40. How about running one at 40 and add one more for each 3-4 degrees lower than that?

Get an accurate thermometer and test it.

The big problem is when the weather report says it will be 32 but a few areas see way lower temps.

This post was edited by GregBradley on Fri, Oct 10, 14 at 22:19

Way too much. I still say protect only when freezing.
I would also like to say that our day/night temps can swing 40 degrees. it can be 30 at night and 70 during the day. Your trees won't be happy in that for the whole winter. Try just bringing them in closer to the house. I leave my potted citrus outside all winter. If it get below 25, I throw a painter's cloth over them. This has worked for: 'Rio Red' grapefruit, 'Tango' mandarin, 'Shasta Gold' mandarin, 'Fukushu' kumquat, and a 'Bearss' lime. Sometimes less is better.

You also need to be concerned about cooking yours trees on a warm sunny winter day. It can get 60F warmer inside my sunroom than outside on a sunny winter day. 120F inside vs 60F outside.

I agree that you are thinking about things that are overkill. Leave them outside except when it drops below 28F. Then protect by covering or moving to a sheltered area.

StickString You have a real good idea with that mini and the X-mas light around the pot. Just make sure you have a good open door on warmish days and use the lights only at night and first part of morning. I heat the roots and foliage to about 75 F roots and 85 F foliage. I have gotten more growth in the cold months than during summer growing season. Even a cloudy day can turn sunny while you are at work. leave a door open every dayand close the door to hold the heat in at night.

My setup in the basement here in fridged Cincinnati

Here is a link that might be useful: http://s1094.photobucket.com/user/wreristhechimney/slideshow/sunshine2013

This tree put on most of its growth in the winter in the box pictured above. The tree is now too big and planted out side and in a lean-to greenhouse that I need as I am in zone 6b.

Best of luck and lets get your tree large quickly and then set out permanently.

Thank you to all for your comments!

Poncirusguy,
Your post's were my thoughts exactly, I planned on opening door fully open before I left for work every morning (7am), and would close door every night before bed. lights would be turned on when temps dropped below a certain temperature. I was thinking along the lines of 45 deg or so?

I understand this is WAY overkill, but it sure makes me feel better knowing these tree's will not have any issues with the cold. especially being that they are so young.

Would you recommend only wrapping lights around the pot, or the limbs as well? I assumed the lights would help heat up the air inside the mini greenhouse, so it really did not matter if the lights were wrapped around limbs or not?

Just the pot. Any bulb touching the limbs could burn the growing surface. Keep in mind, if you forget to open the door just once you can kill the tree. I read some were about someone that planted a grapefruit seed. She warmed the roots each winter and it grew very well all year and reach a fruiting size fairly quickly. I have been looking for that link but can't find it. This was during my research period when I was trying to determine if citrus was worth growing about a year before my first tree.

The other thing to consider is that the branches and foliage warm up very fast and will start growing and that it is the roots that take so long to warm up. My trees are now to big to take them in for the night and out for the day. Be very careful with the plastic.

Steve

Steve,
Thank you for your help/advice. I have attached a pic of the meyer's. I've notices whenever we have a bright sunny day they immediately start to wilt (leaves begin to hang down), although recover overnight and by morning they look much better. I am assuming the rootball just isn't ready for hot sun yet. I have moved them back Into shade and will keep them there until I get them ready for winter.

Now, arn't they looking mighty GOOD!!!

They have turned so green...But don't be surprised if you see signs of stress by them loosing their vigor or rich green color from the cold night lower then the mid fifities..It's just natural..As long as you have them in a good draining mix which it looks like, then they should be ok.
You should be grateful your hours of cold and darness are not as long as mine...That is a great benefit to keeping your plants out..I think your temps don't even reach freezing point until next month, correct? You would be so lucky)

MIke

They wilt on a sunny day because you are cooking them. Black nursery pots in sunny California are a big problem. We are getting to the time of year when they work OK. Also, it looks like you are using Gritty Mix, which dries too fast for the drier areas of Cal.

I may be in a bit hotter/drier area than you but my bigger citrus in Gritty Mix in full sun in 22" square concrete planters, tree/planter/ mix weighing 300 pounds, needed to be watered every morning and evening on most summer days. On the hottest days they needed an extra watering at noon!

First step is get rid of the black. Paint them or something. Sealed ceramic would help hold some water and give some insulation/heat sink. Don't even think about old style Christmas lights on plastic pots in our version of winter. Any bulb touching the pot will kill the roots nearby. We are talking about the old style, parallel wired, bulbs that have a 1/2" base and are about 1" diameter and 2-3" long, right?

I would listen very carefully to what Greg said. I am in the southern edge of icebox USA and have no experience with bright sun, dry air, and mostly warm to hot days all winter. The old style lights I used are the tiny one that don't work if one bulb in the string goes bad.

My 13 watt CFL gives me a 15 degree F temperature rise in my bucket light below. I often use black pots because the absorb heat on cold day. I place a piece of white cardboard in front of the pots on warmer days. Then again, I live in Cincinnati.

If you can keep the roots warm with out over heating them then your tree can grow all winter, but you have to bee very careful not to cook your trees.

Steve

I will be repotting them in bigger pots this spring, hopefully they will be ok in their pots until then?

The potting medium is not the gritty mix but the 5-1-1 mix. I check the rootball for moisture everyday with a wooden dowel and when the pots were in the sun I had to water every two days.

Any fool proof, stupid proof way to keep tree's warm on those chilly nights?

These are the lights I was going to use. My thoughts were it would be "just" enough to raise temp inside mini greenhouse enough to keep me "worry free" during those cold nights

Duh, Now I see the confusion about the lights. HUGE difference in heat output between the two types. It probably takes 10-15 of the ones shown in the picture to equal one of the old style I was talking about. The big issue I see with the little ones is that they are wired in series and one bad bulb causes the whole string to go out. A single 13 watt CFL causing 15 degree temp rise makes sense. It might raise the temp more in our lower humidity.

5-1-1 sounds much better for holding some moisture than Gritty. I'm making Gritty work for succulents out of direct sun but everything else needs more water retention in my sunny/hot/dry climate.

When I had 30 plants in black plastic pots this Summer, I struggled to keep them happy. Putting them in a East-West line and shading the end pots helped a bunch. I think the low humidity makes a big difference because the sun bakes plants here much harder than my previous house on the beach. Our average rainfall for June, July, Aug, Sept is a TOTAL of 1/4".

Great points made about black pots! Sometimes I ever wonder they are even sold or used?

Nothing I have ever grown has grown wonderful in the sun in a bl;ack pot other than desert loving plants..

Don't laugh, but the gritty mix actually held much more water than I believed and cause rot on many of my plants until I learned how to check with moisture on that one even in the hot sun.lol

Now I have turned to either clay, or light colored pots in any shape or fashion, as long as they are not black for those that are going to be sitting in full sun, such as my Figs and Citrus trees.

I had a thought....
As you can see in the photo attached, the two larger meyer's in the picture are the ones I am concerned about. The two little cuttings will be coming back into the house.

My thought was digging two holes big enough to drop both meyer pots into underneath the tree they are under now in hopes of using the dirt to insulate the pots for the "chillier" nights... As for frost, I was thinking of using pvc pipe to make a frame to cover them with some type of material for protection....

Will that work?