What temps kill Coleus & Purple Fountain Grass?

shelli563(zone 6 MA)August 7, 2008

I'm going to try to overwinter several Fountain Grass 'Rubrum' and a Coleus for the first time. I'd like to leave the plants in the ground as long as I can...so can anyone tell me at what temps these plants will die? Do they die instantly at first frost? Should I assume anything below 40 degrees as a good time to bring indoors?



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tapla (mid-MI z5b-6a)

Cold-hardiness is a funny thing, and there are many variables that affect it, so there is no definitive answer to your question. Cold damages plants in several ways. If severe, it damages some of the cellular internal membranes, causing phenolic compounds to leak out of the cell. The phenolic compounds oxidize when exposed to air, causing the damaged tissue to turn black. Slightly damaged plants might cup their leaves downward or wilt. Enzyme activity and membrane fluidity (based on the amount of saturated fats in plasma membranes) are major factors too, and vary by plant.

Cold produces many of the same stresses that are brought on by a prolonged drought. During a cold spell, a plant's ability to absorb or translocate water is severely reduced as its own cells function less efficiently at the lower temperatures.

Obviously, cold tolerance varies widely by species, but within species and even cultivars, genetics are a key factor in determining a plants resistance to cold stress.

Sudden chill from 80* to 50* can be more harmful than gradual chill from 70* to 40*, and dry plants are better able to tolerate chilling. Starting to get the idea of how variable it is?

I think I would try to always keep Coleus above 45-50* for the reason that even though cold injury might not be immediately evident, it can manifest itself later in various ways.

The red fountain grass is a zone 9 plant. I would over-winter on the floor of an unheated garage with an overturned cardboard box covering it to trap geothermal heat. Don't forget to toss a little snow on it from time to time to keep it from drying completely.


    Bookmark   August 7, 2008 at 3:04PM
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ken_adrian Adrian MI cold Z5

no, no, no .... dont try the whole plant ...

in regard to the coleus ...

some time in mid September...

take some cuttings .... in a glass of water ... and root them ...

then .... when rooted... sterilize some potting soil.. pot them up ... and away you go ...

I WOULD NEVER DIG A PLANT AND BRING IT IN THE HOUSE.... unless you want to suffer with bugs all winter .... or plan on using a systemic in advance ... while still outside ...

when the coleus starts to get too tall.. and too leggy .. due to lack of proper amounts of sunlight in winter ... take a few more cuttings and start over ...

in late march .. start multiplying them... so you will have a few hundred to go back outside ... it can all be done under lights in the basement in the winter ...

same with impatiens, begonia [not the bulb type] ....

in regard to the grass ... i have no experience .... but if i were to guess ....

i would divide it into small plants .. and give it a severe haircut right about now.. and pot up 3 to 5 of them .... leaving in full shade ... until about mid-sept ... i would sterilize soil and repot in mid-sept .. to bring them in the house ...

TRUST ME ... gnats will drive you insane in the winter.. in the house... AVOID BRINGing THEM IN ...

good luck


Here is a link that might be useful: link

    Bookmark   August 7, 2008 at 3:27PM
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tapla (mid-MI z5b-6a)

I over-winter perfectly healthy Coleus, the entire plant, under lights year after year with no difficulties. Some are many years old, and insects present no particular problems, so I don't know how someone could unequivocally predict a winter's worth of suffering from insects - just because a plant was brought in from outdoors. If a gnat problem is manifest in winter, it's likely because the grower has had difficulty deciding how much/how often water is appropriate.

Even though Coleus roots easily in water, it's surely not the best route to take if you are starting cuttings to eventually plant out - a well-aerated medium is.


    Bookmark   August 7, 2008 at 4:22PM
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I've rooted coleus like Ken said for a lot of years. I start them in water, then put them in a soil-less mixture once the roots start growing well. I put mine by my sunniest windows. But because they were used to a lot more sun, they do lose some color. When they start getting leggy, I pinch them to get better growth. My coleus that are planted in my gardens get really large and I wouldn't have the room to bring in whole plants. For me, it's much easier to take cuttings and go on from there.
Good luck with whatever you do!


    Bookmark   August 8, 2008 at 1:01AM
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tapla (mid-MI z5b-6a)

I acknowledged that it is 'easier' to start Coleus in water in my post, but easier isn't always the best course.

From a conversation I had on another forum re. the same question:
I know there are a number of reasons we root in water. Chief among them are the convenience of plopping a cutting in water and forgetting it until it has roots and we feel it's ready to pot. I imagine too, that previous failures of attempts at rooting in soil would be a strong reason for some to favor rooting cuttings in water.

Though roots form readily and often seemingly more quickly on many plants propagated in water, the roots produced are quite different from those produced in a soil-like, highly aerated medium (perlite - fine gravel - seed starting mix, e.g.). Physiologically, you will find these roots to be much more brittle than normal roots due to a much higher percentage of aerenchyma (a tissue with a greater percentage of intercellular air spaces than normal tissue - parenchyma). If you wish to eventually plant your rooted cuttings in soil, it is probably best not to root them in water because of the frequent difficulty in transplanting them to soil. The "water-formed" roots often break during transplant & those that don't break are very poor at water absorption and often die. The effect is equivalent to beginning the cutting process over again with a cutting in which vitality/stored energy has been reduced.
If you do a side by side comparison of cuttings rooted in water & cuttings rooted in soil, the cuttings in soil will always (for an extremely high percentage of plants) have a leg up in development on those moved from water to a soil medium for the reasons outlined above.

In the overview: if we're having difficulty rooting a plant in a solid media we probably shouldn't use that fact as an argument that rooting a plant in water, that is ultimately destined to have its feet in soil, is better. The fair question is: If I had the keys to successfully rooting this plant in a solid media vs. in water, which method would provide the strongest plant fastest? If we consider the question carefully, I think we'll arrive at the conclusion that the best way for us, may not always be the best way for the plant. Another way of saying it is ... The best (the individual) we can do within our own limitations is not necessarily the best the (collective) we can do. Please don't read this as a jab at anyone's abilities, because I include myself as part of the "individual we".

I fully agree that if you want to propagate a plant and you simply cannot do it in solid media, it makes no sense to beat your head against the wall. I would do the same thing you guys would, and root the thing in water ... whatever it takes, right? Still, that only makes it variably necessary by individual, not better. ;o)


    Bookmark   August 8, 2008 at 7:30AM
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shelli563(zone 6 MA)

Thank you all for the info...just a question on the coleus...if I decide to put in water, let the roots grow, do I then need to transfer it to the soil-less medium or can it go straight to potting soil?

If I go the route of the soil-less mixture first, will I eventually need to transfer to a potting soil? When do I transfer to potting soil?

    Bookmark   August 8, 2008 at 8:30AM
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ken_adrian Adrian MI cold Z5

great info Al ...

IF IT WERE ME .... an presuming we are dealing with a newbie gardener [if not the poster... anyone else who might read along] ...

i would start today ....

fresh razor blade ... take a few cuttings ... and try now.. so you are sure you will have some rootings by first frost ...

track about 2 or 3 inches down a nice stem ... past the third set of leaves ... and just above the 4th ... and make a cut ... 3 stems ..

take to the work area ... slice a 45 degree angle .. and remove the bottom most set of leaves ..... and place in water ...

replace water in container... whenever it gets cloudy ... thoug i doubt it will happen since these root so fast ...

when you see 1/4 inch roots ... its time to plant ... as Al notes.. its kinda late.. by the time the roots fill the cup of water ....

i would sterilize some soil ... and put into a small 4 inch pot.. plant.. and cover with a baggie.. in bright light.. but not sun ... the little baggie greenhouse will help with humidity.. while some roots are grown to provide water ...

in a week or two ... they will either be dead [which i doubt] .... or thriving.. i would remove the bag over a couple days ... getting it used to ambient humidity ...

if you fail .. you have another month or two to keep trying and succeed ... BTW.. my coleus days ended ... when an unusually early SURPRISE frost.. killed the plants before i was ready to take action ....

my plants .. in the day were 2 x 2 feet ... and my indoor plant stand was 20 by 30 inches ... material has to be very limited in size ... so whole plants were not an option ...

other problems you will have in winter.. is a forced air furnace .. dry air ... and cold windows ... none of the plant i mentioned like any of those variables ...

regardless.. between al's method.. or mine.. or any other one you read about.. EXPERIMENTATION is how you learn .. dont wait until the last minute.. failure is an option at every step of the way ...

anyway .. whatever you do .. just have fun doing it ...

good luck

    Bookmark   August 8, 2008 at 8:46AM
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helenh(z6 SW MO)

I keep sun coleus every winter in my window and under shoplights. The cutting idea is good because you can keep more small plants in your space. I have also kept pots that have been outside over the summer. My plants don't look pretty in the winter, I am just keeping them alive for spring. I start taking lots of cuttings in March and put these in pots after frost danger is over.

    Bookmark   August 8, 2008 at 12:41PM
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Once I plant mine in a soil-less mixture, I just keep them in that all winter. Where my sunniest windows are, the air circulation is not the greatest and if I use a regular soil potting mix, the soil stays moist too long and problems develop. I do keep them about 1 1/2 ft from the windows, because it is colder by the window during winter. Remember to pinch them when they do start to get taller. This will make them branch out more. Just the tops of the stems are fine for pinching.
Like Ken said, experiment. Try starting them different ways. That's how we find what works best for us and the different plants.
Beautiful plants Helen!


    Bookmark   August 9, 2008 at 3:48AM
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I'm also thinking of overwintering my Coleus, begonias, and impatiens....first time, newbie, and these may sound like silly questions, but I have to ask:

1. What do you mean by "sterilize soil"?

2. When you do the baggie greenhouse method in light (I have artificial plant lights)...how many hours of light, or constant light?

3. Can you give me an example of a soil-less mixture? Not familiar with this.

I also read it's important to fertilize them 1x monthly when you bring them indoors. Either a rose/flower fertilizer, or all purpose indoor plant food.


    Bookmark   August 19, 2008 at 1:54AM
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tapla (mid-MI z5b-6a)

Commercially sterilized soils are generally treated with steam to kill pathogens and seeds. Sterile media are better for cuttings because cuttings are in a race to establish roots and a vascular connection to the rest of the plant before rot organisms steal that ability. Excellent media for starting cuttings are: 100% perlite, 100% Turface, Espoma Soil Perfector, or pumice, gravel, coarse sand in the 1/16 - 1/8 size range, chopped sphagnum moss (not peat - the whole pieces of moss).

Cuttings respond well initially to constant light, but I usually keep them under lights on the timer with my other plants 18/6. After they strike, they should have a period of darkness for their metabolism to run most efficiently.

A soilless mix that many use can be found here. Its basis is a 5:1:1 mix of pine bark:sphagnum peat:perlite, + other additives.


    Bookmark   August 19, 2008 at 8:00AM
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ken_adrian Adrian MI cold Z5

link below.. on sterilizing potting media ....

i dont care if the bag claims it was previously 'clean' soil .... i do it myself ....

i have done both the oven and microwave methods ...

dollar store alum. turkey tray .. with alum foil top .... follow instructions .... enough for most of the winter ...

no longer have damp off ... mold... nor insect .. problems ...

a little prevention is so much easier than attempting a cure ...

have you tried rooting some coleus yet???


Here is a link that might be useful: link

    Bookmark   August 19, 2008 at 12:27PM
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Thank you both for prompt responses.

Tapla, when you say a period of darkness, can you be more specific? I'll set my timer for 18 hours of light until I get roots...plant them in soil-less mixture, and then darkness for days, weeks, ????

Ken, I haven't started yet...I came across a few of your posts in the past few days and I think I'm a little behind schedule...I plan to start this week. Hopefully that will give me enough time before frosts and cold temps hit..I think I'm cutting it close. No pun intended.

    Bookmark   August 19, 2008 at 3:04PM
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tapla (mid-MI z5b-6a)

... a daily period of darkness, as the 6 hours in 18/6.

Fresh cuttings = constant light

Once they strike (grow roots) = 18/6


    Bookmark   August 19, 2008 at 4:17PM
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linnea56(z5 IL)

Just reading along. This is very useful! I am saving this thread. Thanks!

    Bookmark   August 21, 2008 at 11:49AM
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linnea56(z5 IL)

If you want to root in perlite, when do you make the transition to potting soil?

(UmmmÂIÂve heard it smells really bad when you sterilize soil in the oven. Is that true? If I wanted to do this I would have to hide this activity. Certain people would object to dirt in the family oven.)

    Bookmark   August 21, 2008 at 12:05PM
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tapla (mid-MI z5b-6a)

Baked soil stinks - true.

I always use a sterile medium for starting important cuttings & never have had trouble transitioning cuttings started in a sterile, solid media to an unsterile potting mix.

Make the transition when the roots have filled the container the cutting is in or when it's getting hard to keep a group of cuttings hydrated in the perlite/other. You can treat the cuttings as plugs if they are singular. If they are planted in mass, break them apart & plant in new medium with root/perlite mass as intact as possible.

If you root plants in water, you can insure a higher % of parenchyma tissue in roots if you float the cuttings on top of a water reservoir (through holes poked in a block of Styrofoam) and use an air stone (aquarium bubbler - you'll need the pump, too) in the water, + a few drops of soluble fertilizer. This produces a very high % of strikes, quickly, though I still prefer rooting in a solid medium whenever possible.


    Bookmark   August 21, 2008 at 12:23PM
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