This is a public-interest archive. Personal data is pseudonymized and retained under GDPR Article 89.

Re: Yellowing Seedlings/Plants

Hi Toni,

> Dear List Members:

> I posted this question previously and didn't get an answer, so here it goes
> again.  My seedlings, which are little at all anymore, seem to be yellowing.
>  I am giving them the appropriate fertilizer (very little).

What kind of fertilizer are you using?  From my experience, which is organically
orientated, I've found that a combination of fish emulsion and seaweed
fertilizer is an effective feed, providing a good mix of major and micro
nutrients as well as some plant hormones.  For seedlings mix up at half
strength and feed once every ten days or so.

> This seemed to start happening when I changed from all "cool" bulbs to 1 cool
> and 1 warm in each unit.  Can anyone address this issue?  Should I go back to
> all cool?  Last year I only used cool and didn't have this problem.

No.  One cool and one warm is a good combination.  The cool provides more light
from the blue end of the spectrum and the warm more from the red end.  Having
both is more balanced and closer to natural light and plants' needs.

> I've also cut back on the hours the plants are receiving light-- 12 on 12
> off.  This hasn't helped either.

While 12 hours is okay, much like the outdoor's daylight length, 16 hours will
give your seedlings more energy and encourage better growth.

> Most of the plants are now potted in "Sam's Magic Earth."

Not familiar with that particular product.  Do you know what is in it?
Some potting mixes aren't balanced for pH very well, often being too acidic
because of the peat in them.  Peat's pH is 4.5, which is too acidic for most
things.  If you can test for pH and find that it is too acidic you can sprinkle
some wood ashes or dolomite lime (NOT hydrated or slaked lime - this is too HOT)
on the soil surface and water it in.

> Any help would be appreciated.

The best growing temperature for most seedlings, and this is a generalization,
is 15-18°C.  If the soil temperature is too cool it can interfere with the
plants' uptake of nutrients.

Overwatering can leach out nutrients, particularly nitrogen and (I think)
calcium.  As well, waterlogged soil displaces air at the root level.  Roots
and soil organisms need some air too, particularly oxygen.

Having some air circulation around the seedlings will help them transpire and
make them sturdier as well.

Here is a general guideline for diagnosing nutrient deficiencies
(from _Botany for Gardeners_ by Brian Capon):

Yellowing of lower (older) leaves first - magnesium deficiency
Yellowing or young leaves first - first symptom of iron deficiency
Weak stems, undeveloped leaves and roots - nitrogen deficiency
Retarded growth, reddish colour under the leaves - phosphorous deficiency
Very poor growth and colour - calcium deficiency

Calcium deficiencies tend to be the most drastic, as it's necessary to form
pectin, the substance that bonds cell walls.

> Toni
> Zone 5

Hope this was of some help Toni, good luck with your seedlings!  Don't forget to
talk to them, they like the extra CO² and good intentions can't hurt either!

Bob

   ____________________
  |                    |
  |     Bob Carter     | Kootenay Bay, BC, Canada
  |  bcarter@awinc.com | Zone 6b
  |____________________|


Atlantic Giant Pumpkins make very poor houseplants
References:
Other Mailing lists | Author Index | Date Index | Subject Index | Thread Index