Winter greenhouse gardening in the SF Bay Area

noahj(9)August 22, 2010

I have allowed myself to be seduced into buying a Harbor Freight 8x10 greenhouse kit. Most of this guy will probably be storage for the various garden tools, but there'll be plenty of room for plants.

What can I really do with this thing during the winter? Are December tomatoes a fantasy?

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calistoga_al ca 15 usda 9

I use my greenhouse,(unheated) for propagation. A heat mat for bottom heat is best for cuttings. With no heat the air temperature will get down to the low 40s in my area, overnight. I try not to store anything in the greenhouse not needed in the greenhouse. You will find there is never PLENTY of room in a greenhouse. Al

    Bookmark   August 23, 2010 at 9:42AM
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wcgypsy(10 / Sunset 23)

I have the HF greenhouse in that size and my first thought is.."Where in the world would I find room to store garden tools?"

    Bookmark   August 24, 2010 at 10:45AM
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Dick_Sonia(Sunset 17)

An important concept to understand for greenhouse gardening is Liebig's Law: the growth of a plant is constrained by the single most limited resource, not the total availability of resources. Imagine that you're building a house and you get deliveries of concrete, rebar, lumber, plywood, nails and so on. You start to pour the foundation, but then you run out of rebar. The concrete, lumber, plywood and nails do nothing to remedy the problem. Until you get more rebar, your foundation cannot be completed and the project is stalled. So now you get more rebar, finish the foundation and start framing...but you run out of nails. Again, the piles of rebar, concrete, plyood and lumber won't help you. Until you get more nails, your project is stalled at that stage.

In northern latitudes, light is generally the most limited resource in winter, both in terms of low intensity and short photoperiod. No amount of extra heat, water or food can overcome this deficiency, in fact, they have to be held back in order to avert root damage. Unless you run high-pressure sodium lights, the available light will limit your growing productivity from early Nov. to mid-March. Regardless of how mild your temperatures are, there is a "celestial winter" of short photoperiod everywhere at your latitude.

What this means is that a greenhouse is a season extender, not a magic enclosure that is immune from the turning of the seasons. Can you get tomatoes in December? Well, if you can get the right varieties of tomatoes to just barely ripen in early November, they should stall on the vine and finish ripening very slowly. You might have a few left in early Dec. that you can pick and leave to finish ripening indoors. They won't taste like summer tomatoes, but they won't be any worse than store-bought tomatoes, either. Mold and mollusks will be a challenge you'll have to deal with in the winter greenhouse.

Spring-sown tomatoes will start to ripen in July if you choose the right varieties. But the same principle holds true: plants will not start sizing up fruit until after the summer solstice passes and the days start getting shorter. Plants are very, very aware of what's going on in the sky and are genetically programmed to enter into certain life cycle stages depending on whether photoperiod is trending toward longer days or shorter ones.

    Bookmark   August 24, 2010 at 8:33PM
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calistoga_al ca 15 usda 9

dick sonia explained very well the limitations of the use of the hobby greenhouse. Arrange a visit to a commercial hothouse tomato grower to see the extent the grower must go to manage the growing of tomatoes in the winter. The combination of light, temperature, and humidity are so critical, most growers today rely on computers to manage them with built in warning systems. It was apparent to me that light was a problem, and caused me to purchase a HID 400 watt light system which works well for my propagation program. Unfortunately it causes a problem with my power consumption and the related costs. Al

    Bookmark   August 25, 2010 at 9:12AM
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Forget the theoretical, what do you folks actually have in your greenhouses?

This is a town where the average bungalow is around 1200 square feet. 80 square feet seems like a huge chunk of space to play around in. I'm figuring on 18 square feet of raised bed in the ground, plus 20 square feet of shelf for starts. The chipper, lawnmower, wheelbarrow and various hand tools go under the shelf, along with a compost bin, and a couple of 50 gallon barrels for thermal mass and rainwater collection. That still leaves 20 square feet of empty space to move around.

Are your greenhouses simply filled with plants that have nowhere else to go?

    Bookmark   August 25, 2010 at 11:24PM
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Axel(12b/Sunset H2)

The discussion about latitude and lack of light for tomatoes doesn't quite jive with my experience. I've had tomatoes grow and fruit right through the Winter in Santa Cruz on a warm southern wall without a greenhouse.It was a sunnier Winter than usual, and the tomatoes were fine. I've ripened bananas right through the Winter, harvest was mid March. This is at latitude 36N.

When I used to live in Southern California, latitude 35N, I used to grow tomatoes right through the Winter and the many Santa Ana days in the mid 80's in January did wonders to ripen great tomatoes. They were not as good and as prolific as Summer tomatoes, but they were yummy nevertheless. When the rains started in February and lasted 2-3 weeks at a time, the tomatoes stopped producing, but as soon as the sun came out they would ripen more tomatoes.

When it comes to fruit growing, I've also gotten crops of surinam cherries in January in a greenhouse.

Sorry, I don't buy the light issue. We're at 37N, it's far south enough to grow quite a few things in the Winter. I get a rather large number of fruits that ripen outdoors in December, January and February, and they all could benefit from more Winter heat.

The bottom line is that at 37N, the bay area Winter limiting factor isn't light, it's cold. True, during a real rainy Winter, there could be a serious issue with lack of light, but even if it rains for a week straight, it will just stall the plants.
As soon as the sun comes out, things warm up nicely.

Just as a side note, whatever you do grow in your greenhouse in the Winter needs to be able to handle cold nights, because no matter what, it will get cold in there. And the long nights contribute to cold soil, so you will need to apply bottom heat, or bury some heating cables in the soil around your Winter veggies.

    Bookmark   August 27, 2010 at 11:04AM
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A little research on this, for your entertainment...

First, I placed the greenhouse in a Google Sketchup model. If you don't know Sketchup, I recommend it, because it is very cool for any kind of design, and you can place a model at precise longitude/latitude and see where shadows fall at any hour of any day. At the best location in the garden, I can get nearly 8 hours of direct sun at the winter solstice. That's about the minimum for tomatoes to grow and set fruit.

For temperature calculations, I got a copy of a program called Virtual Grower, free from the USDA. It's designed to calculate heating costs in commercial greenhouses, but part of the cost calculation is an estimate of solar gain and heat loss. The results are pretty odd. The program calculates that I would need some additional heat to maintain a daytime temperature of 70 and a nighttime temperature of 50 year round!

Leaving aside the possibility that the calculations are just whack, the Berkeley area is pretty marginal for warm-season crops to begin with. Average lows range from 44 in midwinter to 56 in late summer, while corresponding highs are from 56 to 72. So I need about 14 degrees of heat gain in winter to equal the average summer day outside. That seems in the range of possible.

    Bookmark   September 12, 2010 at 12:29AM
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I'm you have tomatoes planted outside that you plan to move into the greenhouse, or do you have newish plants? I've had cherry tomatoes that I forgot to take out of the garden ripen in January (in Sonoma County). Of course, we usually have a hot spell in Jan or Feb, with temps sometimes in the 80s, and cherry toms will ripen much more quickly.

I guess I'm supposing that well-established plants that have been moved into the greenhouse might ripen fruit that's already sizable, depending on temps.

    Bookmark   September 12, 2010 at 8:53PM
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dgbeig(SanFran -z10)

I recently added a small hoophouse to my garden and it worked wonders this summer.
I actually got tomatoes. (pretty amazing considering the SF summer we had).
It was an average of 10 degrees warmer in there, with hot days getting it 20 degrees warmer.

Everything in there produced better than their counterparts outside of the hoop.

For winter, I have some broccoli going, with similar varieties out of the hoop for comparison.
I will plant lettuce and asian greens once I pull the tomatoes.

The hoop is built over a raised bed with some room around the sides for containers if needed.
I will be putting my lemon plants in there over the winter, which should protect them from frost as well as ripen the green fruit already on the plant.

I definitely see the benefit of the hoop, and now I'm wondering how much more of the garden I will cover.

    Bookmark   September 13, 2010 at 6:17PM
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bluebirdie(Z8 SF E Bay)

A few years ago I made a makeshift one about 1/10th of yours. Since it's so small, I only use it to start seeds during winter and spring (but I prefer the top of the water heater when it's really cold). That may be another use of your wonderful new greenhouse.

    Bookmark   September 16, 2010 at 1:49PM
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Following up, about a year later...

I didn't really do anything in the greenhouse last winter. It took me a while to put in some shelves, and there were a bunch of plants in pots. It wasn't until February that I got around to starting seeds.

During the summer, there were way too many tomatoes growing in the greenhouse, plus a couple of cucumber plants. That pretty much filled the place, to the point where I had to hack my way in. Honestly, I did not know that tomato plants could get that big.

What I lacked in variety I made up in quantity. I got about 80 lbs of tomatoes and another 50 of cucumbers during the summer, and they're still going.

Which brings me back to the topic at hand, winter greenhouse gardening. I've got lettuce, cabbage, cauliflower, beets and snow peas going outside. What to grow inside? Will the same cool season crops do better in the greenhouse? Should I just let the tomatoes go on until they stop producing?

    Bookmark   October 22, 2011 at 6:56PM
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I love this discussion!

If I were you, I would just leave all the toms and cucumbers right there and see how far I can push them!

Also, not sure if you are interested in non-edibles; but orchids and other tender tropicals is one type of plants I'd try under the greenhouse, since frosty rain often damages the leaves and plants in general.

    Bookmark   October 27, 2011 at 12:54PM
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OK, I've let the tomatoes and cukes go on. The cukes have pretty much had it. The tomatoes continue to grow and flower, but the fruit takes a long, long time to ripen. But I have ripe toms in mid-November, so that's pretty good.

I also got some of those tubs that are used to mix concrete, about 18"x24"x8", and I've started many of the same things that I have outside. I think the tubs are deep enough for carrots and beets, and the plants are doing quite a bit better than their outdoor equivalents. Mostly, the outdoor veggies are being ravaged by green caterpillars (cabbage loopers?) so growing lettuces, cruciferae, etc in the greenhouse is not a bad idea even though those should be fine outdoors.

Only one month til the solstice! I'll be much happier when the days start getting longer.

    Bookmark   November 23, 2011 at 12:44AM
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napapen(ca 15)

Last January I was preparing to do a seed planting demo. I tried starting several seeds in my hot house which is solar passive, I finally got the seed lights and had some success but I had to leave the lights on 24 hr a day. I put tender plants to overwinter mostly in my hot house and then start seeds in Jan/Feb. A few years back I moved a cherry tomato in a can to my hot house for winter. It lingered and died. Napa does get cold and sometimes the temp was just above freezing and I had sprayed everything inside with cloud cover. I think total length of day has much to do with growing. It's the natural cycle of plants. Penny

    Bookmark   November 23, 2011 at 10:48AM
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So far, so good. It's December 9, and the tomatoes are still going. I grabbed a bunch of them tonight, after three nights of hard freeze, and they're still good.

    Bookmark   December 9, 2011 at 11:59PM
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OK, it is now past the solstice so it is now officially winter. To answer my question from August:

> Are December tomatoes a fantasy?


These were picked today. This is from a greenhouse with no supplementary light or heat. Things slow down a lot, but I do get flowers and they do turn into ripe fruit.

Now we go on to experiment #2. The plants were a mess, with greenery all over the place, including lying against the greenhouse wall. I decided to prune them way back, and see if I could get a new flush of growth. Now things look like this:

Tomatoes are apparently perrenials, so if the plants don't keel over from the abuse, maybe there'll be more 'maters in a month or so.

    Bookmark   December 26, 2011 at 8:35PM
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Thanks for the updates! It was great knowing that you could get such good yield. (How many plants do you have and what variety?) These December tomatoes look so yummy! They look healthy too -- amazing what winter sun can do!

I'd love to hear if the flavor was at least acceptable. I am seriously considering moving tomatoes to a warm corner of my yard and just letting them go this coming winter (which will be 2012 winter).

I have been overwintering peppers this year. I am certain they will make it through the winter. We've had a few pretty cold nights already and they did great!!

Thanks for posting.

    Bookmark   December 29, 2011 at 10:49PM
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Following up a few months later...

The experiment with perennial tomatoes did not work out. They pretty much shut down after the pruning. Still, home-grown tomatoes at Christmas is pretty cool.

This year, I cut way back on the number of plants in the greenhouse, from six tomato plants to two, and it's much more manageable. I've also tried to layer the plants in the greenhouse bed: Strawberries on the bottom, peppers in the middle, and tomatoes up high. This does not work well. The tomatoes and peppers have very deep roots. Strawberries are shallow rooted, so you wind up either overwatering the tomatoes or underwatering the strawbs. And even though you get strawberries a month before you'd get them outside, there's no point in having strawberries in the greenhouse when you have perfect strawberry weather outside. Next, maybe carrots and beets for the lower stratum.

The peppers I planted are the Spanish Padron, which have become very popular. They have a reputation as having variable degrees of spiciness ("unos pican, otros no"). The deal with these guys is that they're quite hot *once they're mature enough to set seed*. So...if you're going to grow these guys...harvest early. They're best when they're tiny.

    Bookmark   August 11, 2012 at 11:32PM
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jkom51(Z9 CA/Sunset 17)

Thanks for the periodic updates! We don't often get those on a discussion thread and it's been very interesting hearing about your ongoing experiments. Keep it up; I'm enjoying following your reports.

    Bookmark   August 12, 2012 at 5:25PM
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Thanks. I posted the follow-up because I've found that the greenhouse has a rather steep learning curve. Even things that should be obvious aren't, and you can only do two or three experiments per year.

That said, the greenhouse has been totally fun. If you're in the foggier parts of Sunset zone 17, you'll be amazed at what a little bit of additional warmth gets you.

    Bookmark   August 12, 2012 at 10:34PM
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