How long to keep heating mat on zinnas?

last year

This is my first time ever starting seeds inside. I got a heat mat and grow lights and Zinnas. Today I seen most of them sprouted. I know I should take off the lid but what about heating mat? I have my tray in the basement which is cooler down there so I'm worried if I take them off the heating mat they'll die. Should I leave it on longer? I'm not planning on planting for about 5 more weeks. Also I can't keep them upstairs because I have pets that will mess with them

Featured Answer

zen_man

last year

last modified: last year

Hi Mandi & socalgal,

I am no particular expert on growing zinnias, but I have also grown them in an unheated basement using Heat Mats. I left the Heat Mats on weeks after the zinnias germinated. Still, I was careful to have the temperature sensor located at a good location to sense the growing medium temperature in the root zone (usually ProMix, sometimes "fortified" with Vermiculite or Perlite).

You don't want the heat mat to "cook" the roots, so the use of the temperature sensor and the temperature setting is crucial. The lights also provide some warmth to the plants, but heat mats can be a big help.

I used layers of newspapers to insulate the heat mats from the metal grids of my chrome steel wire shelving. To be on the safe side, inspect your plants daily. You don't want the heat mat warmth to dry out the growing medium. As long as the growing medium stays moist, the heat mats can speed up the root growth and the growth of the entire plant right up through the blooming stage. Remember, you can click on the photos here to open an enlarged view and close that by clicking on the "X" in the upper right-hand corner.

Good luck with your heat mats.

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Comments (14)

socalgal_gw Zone USDA 10b Sunset 24
last year
Here is a culture sheet for growing zinnias (I tried to make a clickable link but not sure it worked).

https://www.ameriseed.net/wp-content/uploads/2020/01/Zin-Culture-Guide2020.pdf

They recommend 68-75F after germination. Does your heat mat have a thermostat?

p.s. If Zenman answers your question do what he says - he’s the Zinnia expert!
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Mandi (zone5)
Original Author
last year
My heat mat doesn't have a temp control I'll send a picture. I just took off the humidity lid because most of the seeds sprouted and I have lights on I think I will leave the heating mat on for a while just because I'm nervous but keep checking soil to make sure it does not dry out
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Mandi (zone5)
Original Author
last year
Also I seen on utube to put a fan on them. Is that something you recommend or have done
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Mandi (zone5)
Original Author
last year
Yours are really pretty 😍
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zen_man
last year
last modified: last year
Hi Mandi,

" My heat mat doesn't have a temp control "

Wow! That's like a car without an accelerator pedal. Use the fan for the present and take the precautions you mentioned. I also use small fans on my seedlings.

But if you aren't monitoring the situation closely, a fan can increase the drying rate and become part of the problem. So, without a sensor for positive temperature control, your heat mat is sort of "labor intensive." Good luck.

ZM
rosaprimula UK (Cambridge) Z8/9
last year
last modified: last year
I do not use lights or heat at all so am no help regarding your query...however, I will echo what has been said on here - zinnias need heat...and like to be grown fast, without a check. I do grow zinnias most years, but I start them outdoors and sow direct. The big seeds are easy to sow, fast and reliable to germinate and will be growing away in a matter of weeks. Consequently, I get the best out of mine by delaying sowing until the first coupla weeks in May (or thereabouts). Can have cuttable plants in 10 weeks or so.

I totally understand why you would use lights and heat, in a chilly Z5. I used heat mats when I grew onions and peppers because in a mild Z8/9, peppers especially appreciated the longer growing season, after getting off to an early start. , Zinnias, though, are one of the easiest I grow from later sowing in warm soil - growing into robust plants with very little effort. So reliable and stress-free. Do save a few seeds for a later sowing too.

Now I am thinking on it, I always took plants off the heating mats as soon as I saw germination, but may have thrown the odd bits of fleece over at night, if temperatures required intervention.
Markay MD-Zone 7B
last year
Congrats on your sprouts!

I personally don’t use a heat mat. I have a wire shelving unit with LEDs suspended from the bottom of each shelf. even LEDs create surprising amount of warmth. I do have a reflective cover on the top and three sides of the shelf that retains the warmth. The top shelf is always warmest and as soon as zinnias have second set of true leaves, I move them to the bottom shelf. If I were using a heat mat, I would probably take it away once there were two sets if leaves so the zinnias don’t outgrow the space!

i also don’t use a fan. I would consider that optional unless you are having a specific issue without one.
Mandi (zone5)
Original Author
last year
I thought I would start them inside to get a head start because we are not safe to plant till the end of May. I figure if it takes 10 weeks to come up that would be the middle of August and here that's getting to the end of our summer already. I think I may do both though and sow some seeds in the ground too. I've never planted zinnas I'm exited for this summer. I have taken my Zinnas off the heating mat because I was scared to cook the roots and they seem to be doing good. I got a thermostat for the basement it is about 60 degrees F but I do have lights on them so I hope they keep growing good
rosaprimula UK (Cambridge) Z8/9
last year
last modified: last year
O, in a favourable year, zinnia will be up and at it in as little as 6 weeks from germination. I agree with covering all the bases (although I never manage to). Best of luck growing these rewarding and floriferous plants though, Mandi.

Our summers take ages to get going...and this long, cold, wet and gloomy spring, it seems like a forlorn hope...but when we do eventually see the mercury rising (not very much) our autumns are as long as the spring...and frequently more forgiving, warm and a gentle slide into winter. Not unusual to be picking zinnias (and asters, salvias, alstroemerias and leucanthemums) into November.
Markay MD-Zone 7B
last year
Zinnias flower in about 2 months from seed!
zen_man
last year
last modified: last year
Hi Markay,

That's right. You might see a bud in 6 weeks, but it can take a large zinnia bloom several weeks to develop fully. As always, you can see a larger version of the photos by clicking on them and close the larger version by clicking on the "X" in their upper right-hand corner.

Some of those big zinnia blooms are worth the wait.

ZM
Mandi (zone5)
Original Author
last year
Do I keep my zinnas in their seed trays until planting or do you upgrade them to bigger trays as they grow 🤔
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zen_man
last year
last modified: last year
Hi Mandi,

I move my growing seedlings to big 8-inch square pots that sit in trays to catch the drainage from the holes in the bottoms of the pots. My zinnias can actually bloom in the 8-inch "Perfect" (a brand name) square pots, which act as a small container garden. I really like those big pots. They are made of a flexible polymer and are very durable.

ZM
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