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Rule of Thumb?

Posted by davemichigan zone 6a SE Michig (My Page) on
Tue, Mar 22, 11 at 20:51

Is there a rule of thumb on the spacing of seeds and the depth of the planting medium when starting seeds?

I have started some simple flowers like marigold and cosmos. Our last frost date is April 15 (although April 25 is probably safer). I got my first seedlings yesterday, so it means they will have about a month to grow. Is there a point of transplanting them into individual cups, or is it better to just go from the shared pots directly to the ground?


Follow-Up Postings:

RE: Rule of Thumb?

LOL, my rule of thumb, try not to get to many, LOL. Ugh, I am sorry it doesn't have to be that precise, just shake some seeds on the surface and let it go. There are so many seeds that you can just surface sow, which means just to sprinkle a few seeds on the surface and walk away or sprinkle then press.

As far as how deep you plant your seeds well you would rather have the seeds not deep enough than to deep. I seriously surface sow most of my seeds, bigger seeds like moonflower or hyacinth bean yeah I will bury those, but seriously there are more you just sprinkle and press than you bury. Marigold and cosmos, sprinkle and press!!

As for the potting up, well I do not do that either unless it is a tree or shrub. I wait till I see about 2 to 3 sets of true leaves then I plant out in their final location. Now if your growing indoors you will have to harden them off before planting them outside. My advise would be to start your seeds in a container outside that way you will not have to worry about damp off or hardening off.

RE: Rule of Thumb?

Hi Carolyn,

Thanks for your reply!

About the depth, I didn't mean how deep to plant but how deep the soil in the container should be. I first thought the deepter would be better as it would allow more roots to grow, but I guess it would also mean more root damage during transplant; so I don't know which is bettr.

RE: Rule of Thumb?

Well think of it like this. How long do you plan to keep your seedlings in your container?? Are you going to be like me and eager beaver to plant out?? Or will they grow in the container a little to long accidentally of course, lol??

Here is the thing when a seedling is young the roots are more tender. The older the plant gets the more, "harden" we will say, (I know that isn't a great term but it fits) it will get. Meaning if you do allow your plant to "accidentally" stay in your container a little long then it would be best to have plenty of soil, that will depend on what you are growing. For marigolds and cosmos I would say at the very least 4 inches. If you are like me and I can't wait to plant out then I would say 2 to 3 inches will be suffice.

RE: Rule of Thumb?

Dave, if you are not planting them out for a month you may want to plant them up into larger pots, but you didn't say what size containers you sowed them in. My first year of starting seeds I used the peat pellets which are really too small to leave multiple seedling in for a month - I left them in for 2 months (I started to early - couldn't help myself) and they survived, but they pretty much stopped growing after three weeks and were not very healthy plants. As a forum member pointed out to me - "its like trying to raise a baby in a sock"

If you read around on this forum you will see that people do it lots of different ways. Some people want the least amount of trouble, some people like to interact and baby their seedlings.

If you think about the size/depth of containers that you buy plants in from the nursery, compared to the sizes of the plants you are growing, that should give you a rough idea of what you need to do. If they are to crowded it will definitely stunt the growth after a point. And while the roots are tender at the seedling size - the bigger they get - the more intertwined the roots will get - so harder to separate them. A lot of people only sow 2-3 seeds per cell and snip off all but one after they emerge, instead of trying to divide them. much less stress to the plants.

Try different ways and see what works for you.

RE: Rule of Thumb?

I agree with mandolls

Well said!

Maybe for a rule of thumb, for every 1" above surface there should be 1/2 inch below? So a 4" pepper plant should be in a min of 2" container?

That works for most things, not all though.


RE: Rule of Thumb?


Im also in Southeast Michigan. Near Ann Arbor.. Where abouts are you? I was trying to figure out a more accurate "last frost date" Somewhere I read May 6th for my area. Just curious where you got your information?

RE: Rule of Thumb?

cardalin, I am in Canton. If you look at the zone map, most of SE Michigan is zone 5, but there are little spots here and there that are zone 6. It's hard to see, but Detroit is zone 6, near Jackson is zone 5, so I figure I am either 5b or 6a. It is just an approximation and sometimes it is a bet. :-)

What I am trying to do is to get some simple annuals so that I can have some flowers early, but the rest I will do outdoor after last frost.

RE: Rule of Thumb?

Dave, check out the winter sowing forum. There is a ton of info about growing outdoors while there is even FEET of snow on the ground. You don't have to wait till frost is no longer a threat to sow outside.

Here are my containers this january.


Here are a few seedlings I grew in a lasagna pan inside a comforter bag. I sowed them January the 4th and I planted these out this past Sunday. Yes this was all done outside, no expensive lights, no spindly seeds, no damp off, no hardening off, no expensive seed trays.


RE: Rule of Thumb?

Carolyn - are you from the Church of Latter Day Winter Sowing, and on a "mission" these days?

I have to admit that I tried it this year - so you are doing a good job!

The problem for some of us is that our containers still look like that Jan. pic of yours at the end of March. (we got 8" of snow today) It is so comforting to go out and see my little green plants under the lights.

RE: Rule of Thumb?

LOL!!! Hilarious that brought a huge smile to my face.

Well what it is I have always loved to grow outside and this system simply makes sense. So many are scared to try cause of the frost or cold and many do not know they can and when I hear someone kinda newer talking about the cold I have to toss up a picture.

Down in the winter sowing forum zone 5ers are starting to get sprouts so hopefully it won't be much longer for you in zone 4.

I have maybe 85% germinated right now out of 131 containers, my american beautyberry is the newest sprout I found today.

This weekend I plan on sowing more!!

RE: Rule of Thumb?

Glad you were amused - after I posted, I realized that you might be offended - which was not my intention.

Last week we had temps in the 50's for several days but right now it is 9 degrees outside, so its a good thing none of my WS seeds sprouted!

(sorry to steal your thread Dave)

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