root sensitivity

[topshelf12]

  I have a small greenhouse. The first shelf only gives me 28 inches of room which is not high enough for most hibiscus. I was thinking if I planted the pot in the ground it would help me with the height problem.  I only keep the greenhouse between 50 & 70 degrees in the winter. Would that be too cold for the roots? Would they be sensitive to the cold through the plastic pot?
thanks
Norm
San Jose Calif.

[Ernest]

Norm, I don't think you will have any problem with pots in the ground with those temperatures. I grew up in San Jose so I know that the weather patterns are not too different from those here in southern California. I've had almost all my plants in the ground--some for over 8 years. Our winter nighttime temperatures are usually in the low 40s and sometimes down to the mid 30s and I've never lost a hibiscus planted in the ground. My only casualties have been a couple of plumeria varieties that are very sensitive to low temps. Being in the greenhouse should also make it easier for you to protect the plants if a freeze threatens. Where in San Jose do you live?

[topshelf12]

 Thanks Ernest!  I am always thinking of ways to squeeze more hibiscus in .  I live in west San Jose, Hamilton ave Saratoga ave area

[Ernest]

I know the area well. You should have good results with plants in the ground there. We lived in Willow Glen area until I was about ten and then moved a few miles south-- out near Almaden. My roots go pretty deep there since my great grandparents settled there around 1880.
Good luck with your hibs in the ground.

Erny

[farmer d]

Norm I totally agree with Erny.  Having all mine in ground too the only issue I see which you should not encounter is the combination of really wet soil and the cold temps.  Mine are out in the open so a day like today for instance is what I hate.  A really cold rain that just soaks the soil all around my plants.  Add those cold nights in the low 40s or worse and I get really nervous about root fungus especially with the sun angle so low now some of my planters' soil  never dries out till May or June.

There has been a lot of good talk this summer about organic soil treatments especially mycorrhizae.  Chris has done quite a bit of research with it and I like what he has found.  Promoting the good microbes that actually work to eliminate the bad ones like fungus while increasing plant uptake of nutrients (my best attempt to summarize).

The combo of no actual rain soaking your hib soil and adding elements like mycorrhizae should take your possibilities to this next level you're thinking of.  Don't even think twice about those temps in your greenhouse - your plants will flourish in that range.  I know mine don't even blink in that range - just those really cold and wet nights...

Farmer D

[Charlie]

Erny, you've been given sound advice so far. Soil temperature is more stable than air temperature and hibiscus do best in stable conditions. You don't want to go below 50F if possible.

Your idea reminds me of a similar idea I've thought about - digging out the entire floor of a greenhouse down several feet. If the greenhouse floor was 4 feet below the surrounding surface and the plastic covered walls extended 4 feet above the surface it would be a lot more efficient to heat and you would still have an 8 foot high greenhouse. Not practical for most people, but with my greenhouse heaters now draining a 1000 gallon propane tank every couple of weeks I dream about these things!

Charlie