Starting seed in soilless mixture on top of soil to save tra

Hi folks.
Can I fill a red solo cup 3/4 way with my garden soil and the rest of the way up with a soilless mixture to save on transplanting them from cell packs? Thank you for your time.

It will probably work-but do remember to punch holes in the bottom so there is drainage. People use all kind of containers for seed starting. Cups tend to fall over so it works best to put them in a lasagna pan or something else with tall sides.

Remember the two ways in which plant roots are exactly like people:

1. If they don't get enough water, they will get gradually unhappier over a period of days. They come back fine after you water them.

2. If they don't get enough oxygen, they will die dead in minutes.

Garden soil in a cup will tend to compact so much that roots won't get enough air.

If you try a few cups with unimproved garden soil in the lower 2/3, check after a while to see if ANY roots have penetrated the soggy layer.

If the soil was clayey or even "just heavy" to start with, it will hold enough water to exclude all air from the tiny pores that are the only open space heavy soil has. That causes instant drowning, or rather the roots won't even grow down into the waterlogged area.

(Another way to say this is that unimproved soil might only have pores or voids smaller than the thickness of a capillary film of water . Add a little water and you displace all the air. Oxygen only diffuses very SLOWLY through water, or through a solid-water mix like saturated soil. If there were tiny channels big enoguh to be WIDER than two capillary layers of water, then that channel has an open, gas-filled center. Oxygen can diffuse really fast through a gas!

So your soil needs big voids or the roots will drown.

P.S. You can help a little by setting your cups on top of an absorbent pad, that might wick some excess water out of your cups for you. And it makes light bottom-watering easy.

http://allthingsplants.com/ideas/view/RickCorey/646/Bottom-Watering-Seedling-Trays-with-Cotton-Flannel-Prevents-Water-Logging/



If you garden soil is very sandy plus a lot of organic matter, it might stay aerated in a cup for long enough that you can grow a seedling long enough to get it big enough to plant out.

I worry about root aeration a lot. I suspect there is a reason that the word for "root" and the word for "rot" are so similar!

The usual approach is that seedlings benefit from very-well-draining, near-sterile soilless mixes. Garden soil is heavy and loaded with microbes which are as likely to cause damping off as beneficial effects. The layer of soilless mix on top may help with damping off. Also, air movement helps. Also, a dry soil surface helps, so once you get bottom-watering working, maybe lay some bigger bark chips on top of the mix. They will dry out fast but keep the mix moist longer.

If you have a healthy compost heap, that might be a better base for a seedling mix than common soil. You need LIGHT soil that is well-aerated (meaning it must be very well draining).

My suggestion is that, IF you have to use garden soil or compost for starting seedlings, LIGHTEN IT UP as much as you can afford to.

- Coarse Perlite works, but is as expensive as good potting soil.
- Crushed stone or grit (1-3 mm) will also open up soil, if you can find it cheap.
- Pine bark is great and cheap, but you have to screen it yourself.

The sizes should be mostly around 2-4 mm or 1-5 mm. Smaller than 1/4", around 1/8" or down to 0.1". Say, around BB-size.

These "open up" commercial mixes that are fibrous, really well. They should help open heavy garden soil somewhat. If you mixed a little of something fibrous like coir or SPHAGNUM peat and then added grit or Perlite or bark, that would open up soil or compost well.

I'm a big fan of pine bark chips and shreds (or fir, or balsam, and maybe other evergreen barks. I wonder about cedar bark, however!)

I can buy cheap, damp, dirty fermenting mulch form Home Depot and screen it, or clean dry small pine bark nuggets from Lowes, and screen that. I like the small clean dry nuggets - around $4.25 for 2 cubic feet. The worst logyard trash you can find at Home Depot is still around $3.25 / 2 cubic feet.

Bark chunks that are bigger than 1/4" are too big, you can use them as outdoor mulch. Or grind them up and re-screen them.

Since you are trying to "open up" the soil, adding fine bark powder and fine fibers ("bark fines") doesn't help the aeration. "Fines" probably make most soil a little worse . If you have a fine screen, like finer than 1/8", you could try to screen them out to keep the soil as open as practical.

Or, after screening out the big stuff, go outside on a windy day and pour the small screened bark chips onto a tarp where the wind can blow the fines away and into a bed you have, or your lawn. They call that "de-dusting" the bark. Pour the bark repeatedly, "winnowing" it.

Agree with Rick - you don't want to use a heavy soil.
I would also suggest a mixed transition layer. Your water, air, and roots all dislike a sudden drastic change in texture. Not only could you end up with a boggy airless bottom layer, you could also get a too dry "bubble". It could even alternate between both every time you water. In any case, the roots will either avoid it or die in it.
I have used cheap potting soil under my good germinating mix and it worked okay.
Outdoors, I have used a product called "clay buster" with good results. I haven't tried using in pots.
Also outdoors I have started native wildflowers in GOOD native soil in pots using a layer of grit or fine gravel on top.
I like the colored plastic cups to transplant to AFTER they have sprouted in something smaller. If you use a clear plastic cup you can see what your soil moisture is doing. Layering a clear container with different textures of medium makes an interesting science experiment. Not only does water not want to flow from potting soil down into clay, it doesn't want to flow from clay down into gravel, either!

This message was edited Jul 14, 2015 3:06 PM