reduce watering, reduce ambient air temps, and increase air circulation. If you have good air circ and cooler temps and still have it then it is too much water. If you reduce water even more and it still is a problem then the air circ needs to be increased.

Dave

Your pots are too wet. A sprinkle of Cinnamon or camomile tea will kill the algae then let your pots dry out completely. Never go by a time table for watering. Depending on the size of pot they all might need different times for water. Lift the pots if they feel very light it is time to water but some pots won't be as dry so go by each pot. Increasing temperature and air circulation will help dry out the pots.

I only water once a week when the soil is dry. And I literally mean bone dry in the sense that the surface of the soil starts to crack. If I don't water it deep enough (letting the water get sucked up from beneath for about 2-3 hours) the tiny seedlings won't get the moisture they need.

I think the difference this year is that rather than using 48-count short cell packs (per 10x20 tray) I am using 3-inch dura-pots (18 per 10x20 tray) instead. More soil is needed to fill a durapot, but then I won't have to worry about transplanting in a few weeks.

The temp in my cellar is contant, near 65F because by basement is not heated at all. The proximity of my grow lights I'm sure increases the soil temperature but not by that much because they're just plain old T8 bulbs.

In the mean time, is the algae problematic? Should I scrape it off? I'll post some pics later tonight.

Is the algae problematic? Yes. It is a precursor of damp off. But more importantly it is a symptom that shouldn't be ignored. It can only exist in an overly wet environment.

Once a week could still be too frequent. Watering isn't something that sticks to a fixed schedule. And surface soil isn't a valid indication of the need for water. The soil moisture 2-3" down is. So you can have dry cracked surface soil and still plenty of moisture at the root level. The leaf and stem turgor is also a more valid indicator for watering. As long as it firm water isn't needed. Once it begins to soften, to droop, water is needed.

But more likely it is the 2-3 hours sitting in the water that is the cause. That is a long time. Depending on the mix used in the durapots a 3" pot should easily absorb enough moisture within 30-45 min, 1 hour max. You need to reduce that amount of time substantially. Even if the soil surface is still dry looking the roots have had plenty.

It is easy to prove to yourself what the issue and the fix is and many who are convinced they are not over-watering have done it. They simply skip the scheduled watering 1 time when they are sure the plants need it and watch what happens. The plants survive, even thrive, and the molds and algae go away. If they go so far as to remove the plant from the pot they discover the roots have substantially increased.

And there is always the need to increase air circulation - bigger fans on longer - to dry out the area more.

Dave

Great advice Dave. I will definitely reducing watering as you recommend. Now the question remains, do I remove what algae I currently have manually or will it go away on its if I add a couple of large fans in the vicinity? How long before I should expect it to disappear?

Here are some photos:

I would just scratch up the surface a little to aerate it and help drying. Once you reduce the watering the algae should dry up and die off. Now we can see the problem I'd say that the discoloured cotyledons on the Pelargoniums are also a symptom of over watering. Is the mix very peaty? Peat is difficult to get hydrated evenly and consistently imo.

I did exactly that late last night... scrape off the tops gently with teaspoon. Should I top off the containers with new dry growing mix to account for what I scraped off?

I am using the Espoma Mix this year instead of the Dr. Earth's that I used the last two seasons. Pics below.

I start all my seeds in 4" pots, but NEVER bottom water them. EVER. Does the trick for me. No issues with damp, no issues with shallow roots, no issues period. Some people like to bottom water, to me its a pain and can cause issues like you are seeing....it takes FOREVER for containers to dry out, never a good thing with small seedlings.

Interesting. I've always been told not to water from the top. Ever since I've scraped off the algae and only bottom watered for an hour tops I've been seeing my containers dry out quicker. It also helps that the room I have the containers in is the area of my basement near my furnace. Not that it's warm in my basement or anything (unheated, actually about 64F-66F) it's that the air is bone dry.

I have heard lots of people say "don't water from the top". Heck, Mother Nature most always waters from the top!! For me I get way better water control by NOT bottom watering. Soilless mix, fans, and not overwatering, has always worked for me. No damp off, no seedling loss. Has worked for over a decade for me :)

What happens in nature isn't totally relevant because in nature there isn't a drip tray preventing excess water from draining away. But either way - top or bottom - it's learning to recognise when plants need water that counts. I water top or bottom as is convenient. Has worked for me for five decades ;-)

Yeah, Mother Nature doesn't grow her plants in containers. :) But even if her rains falls from the top the actual watering of the plant takes place from the bottom as that's where the roots are.

Dave

Well jeez. Of course plants take up water with their roots, Mother Nature doesn't grow in containers, and we have drip trays! What I was getting at is....in their native environment, plants are exposed to water from above ALL THE TIME. Top watering doesn't kill plants, we humans do :)