Greenhouse humidity

There have been many questions recently on humidity in the GH. I have written a couple of things on this subject and I synthesized them here in an effort to answer as many questions as I can. Sorry if long, overly technical or boring.

Proper greenhouse humidity is important both in preventing plant diseases and promoting healthy plant growth. High humidity can have several effects. It may promote the Botrytis and other fungal diseases. It restricts plant transpiration, which in turn limits evaporative leaf cooling and can lead to overheating of plant foliage. If high humidity persists for a long time, the restriction of transpiration can limit the "transpiration stream" of nutrients and can lead to nutrient deficiencies.

Low humidity has it's own problems. It may increase foliar transpiration to the extent that the root system cannot keep up, or to the point that the leaf stomata close in the plant. This stomata closure minimizes the water loss, but it also reduces CO2 going into the leaf, decreasing photosynthesis and bringing growth to a standstill.

Plants don't care about relative humidity. This is what most devices, including mine, measure. Plants care about absolute moisture content. Scientists measure this as the vapor pressure deficit, or VPD. This, in absolute numbers, is the difference between the amount of moisture the air can hold when saturated and the amount of moisture the air actually contains. The higher the VPD, the drier the air. The lower the VPD, the more humid the air. You can think of this as the "drying power" of the greenhouse air. To convert between RH and VPD you have to use a chart or complicated mathematical formulas. Here is a spreadsheet calculator that will do the conversion for you; go here: http://sheet.zoho.com/public.do and search for or click "Calc-dewpoint-VPD."

So, where do you want to keep the GH humidity? Fungi survive at a VPD of less than 0.4kPa and a VPD of less than 0.2kPa promotes fungal growth. High VPD (drier air) corresponds to a VPD of greater than 1.5 or 2.0. Ideal VPD for most plants varies but most sources list somewhere from 0.5kPa to 0.95kPa. Using the chart in the links I have below, you can see that a VPD of 0.2-1.0 kPa corresponds to a RH of about 40-87% at 15*C (59*F) but corresponds to a RH of 77-96% at 30*C (86*F).

Low humidity can be managed with misters and foggers. It is also useful to shade plants under conditions of low humidity to reduce the rate of transpiration.

Managing high humidity starts with ventilation...replacing warmer, humid greenhouse air with cooler, drier outside air. Ventilation also involves significant energy losses, and therefore ventilation often must be accompanied by heating. Therefore, lowering greenhouse humidity with a combination of ventilation and heating can cost a lot of energy.

My experience is that humidity is the hardest of the GH elements to control. Low humidity is not so much a problem as high humidity. Humidity can be raised with foggers, misters, and generally you'll do this in the summer. Dropping the humidity is more of a challenge and is generally done either by venting and heating. Most growers simply aim to avoid the extremes of humidity. Over most temperature ranges, a GH humidity of 50-85% is generally safe.

I hope that helps someone out. ;-)

http://www.hortnet.co.nz/publications/science/n/neder/humid01.htm#top

http://ohioline.osu.edu/aex-fact/0804.html

Edited to add the VPD calculator in this first post.
This message was edited Nov 25, 2007 11:49 AM

This message was edited Nov 25, 2007 4:21 PM

That is a great thread, SB, thanks for the info.

In regards to using venting to reduce humidity and the costs involved, my grhouses are larger than the norm here, and so I am not sure if this relates,but I hardly ever think about the humidity in the grhouse. I do avoid misters, foggers etc because I don't want the extra humidity that that can bring-esp at night. I would never run misters etc in the evening when the fan is not running-which gets to my main point. In the evening the heater runs (or not, depending on the temps outside) and I have small circulating fans that run 24/7. But when the sun comes out in the am and the grhouse starts to heat up, by the time that the humidity would start to build up, the fan comes on and replaces all the air in the grhouse and will continue to do so until the sun is no longer on the grhouse or the temps drop enough. Rarely is there any excess humidity between the time that the fan shuts off and the heater kicks on. So what I am saying is that if your temps are set correctly on your thermostats (for the fan and heater), then high humidity should not be a problem.

Are you refering to the cost of running the fan in the day as the high cost with ventilation in controling humidity? If so-I dont see how it is avoided. If my fan doesn't run on a sunny day, the temps will quickly climb over 100 degrees. I know that with a larger grhouse that the heat builds faster-more space under plastic in the sun to trap the heat, but doesn't everyone that has a grhouse in full sun have to run their fan during the day? Wouldn't that take care of the humidity?

Hi TL,

You are zone 7b. It sounds as if you have your exhaust fan in use all season long. Most of us in cooler climates do not. In fact, my exhaust fan is unplugged and covered for the winter. I do have an operable ridge vent in case I need some ventilation. The costs don't come from running the fan (or the ridge vent in my case). The costs come from heating the cooler, drier outside air that is brought into the GH to reduce the humidity.

Ok -first, that blows my mind that you guys do not have to run a fan during a sunny day in the late fall/winter. Assuming that your grhouse is in full sun-what are the high temps in the early afternoon? What happens if you get an unusually warm day-say in the 60's and sunny-is the ridge vent enough to cool the air down?
Are you attempting to keep a 15 degree or so differential between your high and low temps in the winter? Speaking just for me. I am actively growing plants during this period, not just maintaining them, but I would think others are growing as well.
Yes the humidity would be the highest in the early am, but it is for a short amt of time (for me) so I do not worry about it. It is the prolonged conditions of high humidity that I worry about-those days that are warm, but cloudy and the fan does not come on-that is about the only time (that I can think of right now) that I think about humidity-and will come in and manually turn the fan on for a few minutes to replace the air-or set the thermostat a few degrees lower (and then try to remember to turn it back up the next day! lol)
In respect to heating the colder air from ventilation-for me, the fans turn off well ahead of the time that the heater comes on, and during that time, the air has warmed up some, i.e on a normal winter day, the fan turns off around 3 or so and the heater starts up around 5-6 pm. In other words, the heater is going to come on then, regardless of the fan. I could have no fan running and the air would have cooled off in the grhouse around that time due to the air cooling down outside.
This fascinates me-the differences in maintaining and running a grhouse due to both size and zone. I realized awhile ago that in most aspects, when it comes to running a small grhouse, my experience is nil! Now I am trying to understand the conditions in a small grhouse. Very interesting.
One similiarity-in trying to keep humidity down, I never water in the evening. Even if a plant is dry, it doesn't get water until the next am. For two reasons. One-roots grow at night and they need oxygen to grow and water displaces oxygen. Second-wet foliage at night is a invitation to a fungus.

I'm totally with you on evening/afternoon watering. I have noticed, especially in the winter, that a plant which is dry and droopy in the late afternoon might be dry but perky by the next morning. I try to wait until the next morning to water them.

A sunny winter day might get me to 80F. The ridge vent will repeatedly open and close on those days. That is about 22F differential between high/low. Most days are far less than that. Today is it cloudy, and I bet it doesn't go over 62F in the GH.

I think these difference you note are more zone dependent than GH size dependent.

they might be zone dependent-but i have noticed that there are quite a few grhouse owners that do not have a fan on a thermostat in here. They might have a fan on a outlet or just a ridge vent etc. I am thinking of those grhouses and wondering about how they cool the grhouse down-esp when spring comes and the outside temps start to increase and the sun's strength increases. I could never do that with a larger grhouse-but maybe it is possible with a small grhouse. That is something that has piqued my curiousity.

I have a very small greenhouse (5x9) and I take the very low tech approach to ventilation--I open the doors slightly anytime the day's going to be sunny, then close them up again in the evening (and as we get toward spring and the weather gets warmer, I open the doors farther and farther during the day). If I don't open the doors, on a day that's sunny and low 70's (fairly typical for our winters), temps in the greenhouse can easily go over 100, but if I crack the door open a bit, it keeps the temps much more reasonable. I also crack the doors open on days that I've watered to let some of the excess humidity escape.

thats amazing, ecrane. Once in a blue moon the fan belt breaks (I have learned to keep extras on hand and to inspect them more) and just opening the door does absolutely nothing.


On another note-I forgot which thread was about plastic grhouses and the temp inside being close to what was outside and also squirrel cage fans blowing air between the layers of plastic as a type of insulation-so I will post my findings here SB. I just recovered my grhouses and replaces/fixed my squirrel cages fans and the other morning it was 27 outside and I went in one of the grhouses before the sun was a factor and it was 40 degrees! That is a nice jump in degrees to see.

I have been very concerned about how high the humidity runs in my GH, so this trhead and others have been a big help.

I am also in Zone 7b, and it is very humid here most of the time. I have been tweaking the thermostat on my exhaust fan, and my heater trying to get the humidity down.

As has already been noted, my humidity is always the highest in the early am. Now that the days are short and it is cooler outside, my exhaust fan does not come on as often. I was letting it get up to 85-90F for awhile, but it was just staing too humid, usually about 90% most of the time. I have lowered the thermostat to 80F, and now when the fan comes on I can see the dip in humidity.

Of course I can't have the fan on at night as it is too cool now, and also many times as soon as the sun goes down and the temps drop, the humidity outside rapidly climbs, and before the night is over it will be more humid oustide than it is inside the GH.

I had to go back to IL for a bit, so just before I left I turned the thermostat up in the heater. By raising the temp I have noticed the humidity has dropped to a tolerable level.

I run three circulation fans inside the GH. One fairly high volume fan down oneside, another smaller fan on the other that is also pointed toward the ceiling to move trapped hot air from the peak, and I also run a small circulating fan on the floor, under one of the benches.

The sensor I use to monitor temp and humidity is also under the bench on the back wall. I have another temp and humidity sensor that sits on the top shelf. I noticed the morning after I turned the heater thermostat up that there was about a 25% difference in the readings of the lower sensor and the upper.

When I get back home I plan on moving the sensor up above the lower bench and below the top shelf and see how much the readings change.

As I am so new to ALL of this, not just my first GH but my first at trying to grow things in general this thread has been most useful. Thanks to all that have contributed.

The graph I am enclosing is a plot of the last four days of the conditions in the GH. I have superimposed two red line that show where the fans came on, and how the humidity dropped at the same time.

I think I will have to continue tweaking as I don't think I need to run the GH at 70* at night.

Would it be feasable for a hobbiest to just purchase a de-humidifier and run that? I am not sure it would be cheaper to run that then it would be to just keep the temp a little higher.

Sorry this is so long, thanks for all the help and advice here.

Nautical

tigerlily--I think the reason opening the door works for me but not for you is because my greenhouse is 5 by 9 and yours is way bigger than that. The door is along the 9 foot side, and it's a pretty good size opening, so if I have it open all the way the greenhouse temps come down pretty close to the outdoor temps. We also pretty much always have wind here, I guess if the air was really still I might need fans to bring in the cooler outside air, but with our breeze, the cooler outside air blows itself in without any help if I leave the door open.

Skip, I think you numbers are fine. Just eyeballing your graph (very nice, BTW), you are running 80% RH and around 70F most of the time. If you calculate the VPD using these numbers, you have a VPD of around 0.6kPa, and that is certainly acceptable.

This morning I had 61% RH and 63F. I get a VPD around 0.7.

I will see if I can make a little calculator that will give you the VPD.

Skip, others, disregard previous versions, there was a bug.

Here you are: http://spreadsheets.google.com/pub?key=pXu226ToNOVn2ijNK94ZxCg

SB

Edited to say rats, anyone can view it and nobody can plug in their own numbers. I think I tried this before and couldn't get it to work. Dmail me if you want the file.

Edited again, what else do I have to do today? Try this link, then search or go to Calc-dewpoint-VPD: http://sheet.zoho.com/public.do

This message was edited Nov 25, 2007 12:32 PM

This message was edited Nov 25, 2007 12:52 PM

This message was edited Nov 25, 2007 1:04 PM

Hi Everyone, this is a great topic and one that could make all of us do some thinking.
Thursday it was 70 plus deg. outside, today it is 40 deg. The GH has been going up and down like crazy for four days. In a 24 hour period I not only have had the heat on, but the fan on and the vents open. Today it went from 48 deg. (overnight) to 82 in full sun in the GH. That kept me stepping. The humidity was up and down also, but I was more concerned about the temp. It is almost impossible to put the thermostate on at night and keep it from getting too hot before I get out there about 8:30 or 9:00 A.M. if the sun comes up. The sun is still very warm and the GH is in the full sun here also. I am very much like Tiger temperature wise but cooler. The humidity here is unpredictable from morning to night. We are only about 20 miles from the ocean and depending which way the wind is blowing our temp and humidity changes within hours. My GH is only 8 x 12 but I could not do it without a fan even on a day like today during the suns warmest hours. I have less trouble keeping it warm at night than I do keeping it cool enough during the day. Go Figure!

SB, Thanks so much for your work. I am sure you had nothing better to do today...... :-)

I was able to export the file so no need to d-mail it. I will run the numbers often until I get comfortable with what is going on in the GH. I can see from here that the temp stayed flat today, indicating the sun did not come out. Humidity climbed all day outside, but held in the range I need in the GH.

Your posts on Temp, Humidity and it's effect on the plants has been most helpful. I have been guilty of watering in the evening because I noticed a plant looking wilted. I have also noticed plants that looked wilted in the evening, but in the morning looked just fine. What I have learned here I will use and not water at night just because a plant looks a little stressed.

I have read about some kind of fungus (Botrytis?) that can attack the roots and spread very quickly in the GH if the humidity is kept too high, so that has been a big concern to me. I had planted an area of Lamium last summer (2006) that had done very nicely and was making a good ground cover. This year it came back, but suddenly died within just a matter of days. I asked the folks that treat the lawn for weeds and insects, etc and he stated that the soil was very wet there and that most likely it was a root fungus that killed it. Ever since then I have been concerned this would happen in the GH if I did not get the humidity under control.

Is there a chemical that should be applied periodically to help prevent this?

Anyway, all this info has been a big help.

Nautical

Nautical-this one i can take! lol Unfortunately I know all about fungus and chemicals to treat them.
The vast majority of fungus that occur from high humidity in a grhouse are surface/foliar fungus-they result from the foliage continually having moisture of some kind on them-or from the foliage being so thick that it doesn't allow for air circulation to get in there and dry it out. The types of fungus that happen in these situations are: boytritis (this is not a root fungus as you thought), rhizoctonia (which actually attacks the stem-also known as "damping off" -common for seedlings, they keel over because the stems rot-too much moisture on the plant (misters and foggers are usually the culprit here), powdery mildew, anthracnose, downy mildew etc. They are all treated with daconil, clearys etc. Proper way to treat is to add a surfactant and spray the foliage and keep the foliage dry for as long as possible afterward. Also remove all infected leaves and put in a garbage bag and throw away. Remove the leaves everyday until the fungus is gone-spreads by spores in the air.

Root fungus are usually brought on by soil that is kept on the wet side and never allowed to dry out. There are several fungus that occur here-pythium (also can attack the crown as well as the roots and is known as crown rot and also damping off-which is also one of the common names for rhizoctonia-which is a shame because they require different fungicides to treat-so confusing to some), phytopthora and sometimes thielaviopsis (mostly pansies).
The same fungicide is used to treat the first two-Subdue, Truban or Alliette. These 3 are all root systemics and last 30 days and are very expensive. Thielaviopsis is treated with Clearys and other fungicides that are a bit harder to get. They are all know as soil bourne fungi and are spread by watering (the spores are spread by the water splashing from one container to another, using the same tool from an infected container, or bed to another, or using a container that had the fungus in it with a new plant. Also if you have any of the above fungus in a container-throw away the container in the garbage. These spread fast and are the hardest to get rid of.

The best treatment for avoiding a fungus is preventative growing procedures. Sterilize your grhouse periodically and your containers before reusing. Grow on the dry side-only water a plant that is dry (or if it is the am and you know that the sun will be out and higher temps outside and the soil looks fairly dry-then water it. If cloudy for the day, then don't water) and only water in the am/early afternoon. Stressed plants are more susceptible to a fungus. Which makes you think that you should water it, but its always walking a fine line on when to water sometimes. I always say that watering is the hardest job in a grhouse-knowing when and how much. It is the first thing that i teach a new person-and it is confusing to them until one day they "get it". I always say "go spotcheck" a grhouse-that means watering only what is dry, or what you know will be dry by mid afternoon (esp sunny, hot days). There are certain places in all grhouses that are hotter in the day and dry out sooner. For me, it is the row of plants on the sunny side right up against the plastic and also close to shutters where the wind blows the most.

Air circulation is another important feature of keeping your chances of getting a fungus down.
I think most times if you don't overwater and have good air circulation throughout the grhouse, then you shouldn't have to worry about a fungus. That said, as a commercial grower, i do use a preventative spray when I first transplant seedlings, cuttings or plugs into pots. I use either Truban or Subdue and Clearys (at half strength) and then grow on the dry side, and don't spray again until I see a problem.
I hope that this helps!

TL,
THANK YOU! I will copy this post and paste it into my database that I use for keeping track of the GH.

I have daconil, but was not sure what or how to use it. It is in a hand held spray bottle that I got at Lowes I think. Should I apply it once in awhile as preventive maintenance? I am not familer with clearys, is that something I can get at a garden center? Or is it only available to professional growers like yourself.

I think I am doing ok with the air circulation, as the leaves on the plants are not wet. But I am DEFINATLY over watering. I have some things that just don't dry out.

I have one of those inexpesive moisture indicators that I use to check if I am not sure. Particurlarly on large deep pots. (I can't vouch for how accurate it is, but I have tested it on pots that were very light and dry against pots that were heavy and moist and it seems to work ok.) I have two Plumeria cuttings that I am trying to root in a cactus mix I have used sucsessfuly before. I have not watered those two pots in over 2 weeks, but they are still very heavy and wet. I have them on a heating mat with a soil thermometer stuck in. The soil stays around 80 degrees. They have been in those pots for over 4 weeks now. They look ok, but there is no sign of new leaves on them. Just before I left I tipped a grow light so that they would get full light for awhile.

I am not sure what a "surfactant" is that you mentioned. Is that just some soapy water added to the chemical to be applied?

Thanks again for the precise explanations.

Nautical
ps. I just ck'd, it is less than 1,000 miles from Conway Ar to Raliegh, Just a long days drive. Let me know when you are ready to swap some free labor in exchange for "watering" lessons!" :-)

lol thats 16 hrs of driving! You would have to hold a gun to my head before I did that! Thats what they made planes for!! :)

watering is simply reading/seeing your soil color. I basically use one type of medium to grow in-sometimes I add extra perlite for more drainage, or bark etc, but I know this medium well and I can tell just by looking at the soil if it needs water or not. As the soil dries-it changes color and the more you look at it, the faster you can tell whether to water or not. Also, as I said above-knowing the weather for the day goes into the equation.

Most of the palms that I get from Hawaii come in a cinder/volcanic rock that I am not used to and I cannot "read". 3 times now I have killed a palm by letting it dry out-literally right before my eyes! I have now decided, (finally!) to never leave them in that medium-I will kill them everytime. I obviously take awhile to "train" lol

TL I learned that lesson of changing the soil to what I am use to with my trades here on DG. Every area has something different that works for them. If I get a plant in I immediately repot it into my mixture and have much greater success doing this.

Jeri

Tiger or anyone! Please tell me where I read something about little roots grow better dry and wet? Did I read it or did I make it up. I thought it was in this forum but now I can't seem to find it. I wanted to read it again. Thanks for your help.

JBerger-I think it was me, and I said to water in the am so that the roots have a chance to dry out before evening as the roots grow at night, and they need oxygen to grow, and water displaces oxygen. Dryer soil also promotes healthier growth and less chance of roots rotting.

Thanks Tiger, I thought it was you. I wanted to be sure I was doing what you were saying because I lost alot of seed to dampness when first started. I thought you said you did not water in the p.m. Thanks again.

Well-starting seeds is different in some ways than growing plants that are fairly established-which is what I assumed we were talking about. Sorry-i didn't catch that about seeds.

Seeds water requirements are a bit different in that their root systems are much smaller-so they can't dry out like a larger plant. Are these seeds that have just germinated-or seedlings with their true leaves?

I've a question please, could someone help calculate my makeshift gh's VDP, say 64% humidity, 68 degrees F. Another reading in the morning sometime the values 84%, with the constant 68 degrees F. Is the environment conducive for growing and blooming plants?

64% 68F is VPD of .84kPa
84% 68F is VPD of .37kPa

The second might just be a tiny bit too humid, but the first is perfect.

SB

Thank you, SB. I'm pleased, I've some brugmansias that are forming buds, I was afraid they may not bloom well. This gives me much hope to see more blooms during the cold days of winter. Your help is much appreciated.

Tiger, the seeds I am growing area dougles fir, balsam, concolor and eucalyptus.
I usually make sure they do not dry out even if I leave the others get dryer. Yet. I can not let them soaking either. That is when the fungus or whatever the heck it is takes over and rots them off. I have about 30 little tiny two inch trees just now and some have not even begun to sprout. It is so difficult because they need to get cooler for part of the day. When they do sprout I take the cover off the flat during the day and put it back at night. The past two nights I left them off because I wanted them to get the morning sun since we had so many cloudy days. They are really touchy.

I don't know the first thing about germinating tree seeds! But if I understand what you have-its that you have a seed flats in which some of the seeds have sprouted and are 2" and there are still seeds in there that have not sprouted-so you are trying to juggle between the dryer soil for the sprouted ones and wetter for the unsprouted ones? If so-thats alwasy a tough one. You can either carefully transplant the sprouted ones (don;t they have tap roots-where you have to transplant fairly fast anyway?) or make sure that the unsprouted ones have soil over them, and just wet down the seed flat in the am, and the soil should keep the seeds moist enough until the next am.

Was that the situation that you have going?

Hi Tiger, Sorry to be so late in replying, but my dog has been so sick for days, the weather sucks, cold, snow, rain, whatever, today it is so windy I am at my wits end with trying to keep those little guys alive and well. HA! To answer your question, yes, that is what I am doing. It will take some seeds longer than others I realize that but they are so fragile I am afraid to transplant them just now. The temperature is driving me nuts. The windchill is in the 20's and the actual temp is about 35, the greenhouse fluctuates all the time because the sun keeps going in and out. I am not having a good time. It got so cold the other night I have some yellow leaves on my jasmine. Waaaahhhhhh! My first winter with the greenhouse so I am learning the hard way.

JBerger-sorry to hear about your dog-I hope he/she is ok now.
Don't worry about the sun coming in/out during the day-that is what the fan/thermostat is for! I think you have one? Sorry-can't remember-all these grhouses in these threads are merging into one in my head!! However the night time temps are different-they should remain fairly steady. What do you have your heater thermostat set on? Is it high enough? Is your heater big enough? Sometimes plants get yellow leaves from drying out too much.

In a natural setting,temps flucuate too-as they will in a grhouse. Its not that big a deal, assuming that the temps aren't in the 90's during the day and in the low 40's during the night.

Don't be afraid to transplant small seedlings-and 2" high is a huge seedling!! I have tranplanted begonias before that were the size of a pinhead, you could hardly see them. Seedlings like to be transplanted-it stimulates root growth and you will usually see a lot of growth after you transplant them. Try one and see. Just ease your finger up under the seedling and gently/slowly pull up on the seedling as you move your finger under the soil to loosen the roots.

In responding to the plumeria rooting during the winter months. I winged it last year, as so long the temp. is above the 70 range. I kept mine in the kitchen's window box. There will not be enough energy expenditure with the moderate environment, thus the roots will take hold first, long before you will see leaf-growth. And that won't be until we take them outside in the spring when the temp. is adequately warming up.

JBerger,

I find using an ordinary teaspoon from my kitchen the best transplanting tool I've got for seedlings. It lifts just the right amount of soil with them.

MollyD

I use one of those hard clear hard plastic spoons. My DH would have a heart attack if I used one of the real ones and brought it back into the kitchen. He's funny like that!!!

Jeri

Jeri,

My Paul would never notice ;-) but I just leave it with the plants anyway.

MollyD

My DH notices everything!!!! LOL!!! I fool him sometimes!!!

Jeri

Thanks everyone. I must find time to transplant a few things really soon. I will include a few seedlings just to see what happens. The temp went down to 45 in the GH last night but it quickly came back up when the sun came up. I think I worry too much. I have some new plants coming this week. I will tell you what they are when I get them. Must go make wreaths and cones and grave blankets to sell this weekend. Later.

What are grave blankets? Is that something yall do up north?

Jeri

The reason that i like to use my finger is because I can feel the roots separating from each other as I gently work them apart. When all the roots of the seedlings are growing together so closely, and the seedlings are so small, I guess I feel I have more control over losing less roots when I can feel the roots. Sometimes when there is a large block of them growing together, I will pull that block out of the soil and start to pull the seedlings away from the outside of the clump and work my way inwards.

I was gonna ask the same thing, Jeri. What's a grave blanket? : )
~Lucy

I've never heard of grave blankets and I've lived most of my life in the north!

MollyD

Grave blankets are pieces of holly, evergreens, other greens that look nice and stay alive like the evergreens and you put on a metal or wood frame that is shaped like a cross or an oblong block and then you decorate with bows, and other Christmas stuff. When finished they lay on the grave and you stake it down with a piece of heavy wire like a coat hanger so the wind does not blow it away. They use those in the winter here in the north. You can pay anywhere from 20 to $75 for one depending on what you want.
I make a simple cross with a bow in the center and sell them for $25 to $35. I will try and find a picture of a couple I did for a customer last year.