Paul4444
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Problems with bottom watering

Hi

I'm new to starting seeds indoors and I've been having a few problems that I hope you guys can help me with.

Firstly I'm growing a few annuals and perennials in promix organic seed starting mix in 60 pot flats. I have been having great success germinating the seeds using a heat mat but the problems start after that. The seedlings come off the heat mat as soon as they germinate and go under 2 t5ho lights in a room with a temp of about 67F. I have a 12 inch oscillating fan placed about 5 foot from the seedlings. My main problem is a white mold that grows on the surface of the soil. I'm bottom watering by adding water to the tray up to the drainage holes on the plastic pot and leaving it for a while until the surface is wet. The surface feels soggy rather than wet which I didn't think should happen when bottom watering. The surface of the soil still feels wet the next day and I think this is my problem. I only water the seedlings once about the top half inch of soil is dry. Can somebody please suggest what I may be doing wrong and how to fix it please. I was thinking maybe not letting the top get wet and remove the water when I just see water appearing at the surface.

Thanks

Paul

imafan26
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How long are you leaving the water in the trays when you bottom water. Most of the water should be wicked up in 10 minutes, if it sits for longer than that there is too much water.

Since you are using a fan, the top of the soil will dry out faster than the bottom. Try weighing the trays when it is dry and when it is soaked and let it get almost to the dry wt before watering again.

Paul4444
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Thanks. Up until the last watering I was just leaving for about 10 minutes, I read on this site that people leave it longer. How far down in the pot would you let get dry. The pots are 2 inches deep with soil about 1/2 an inch from the top. Should the fan be closer?

Thanks

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rainbowgardener
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You said 60 pot flats and then you said the "pots" are only two inches tall. Are you talking about the little cells?

Image
https://thumbs3.ebaystatic.com/d/l225/m/ ... Pn39tQ.jpg

To start with, using the little cells, I would fill them all the way to the top. I fill them with potting mix, then pour a little water into them from the top (before anything is planted in them), stir to mix/settle, and then fill again. That is such a little bit of soil space, you want to use it all. And if you plant seeds below the cell wall level, then they could be shaded a bit. It will also give you a bit more "soil" to soak up the water.

It does sound like you are getting things too wet. If you lightly press on the potting mix surface and any water oozes up, it is too wet. Use less water or remove it sooner. I actually don't take water back out from my trays, but for me just putting a quarter inch or so of water in the bottom works ok and the tray is dry again the next morning. If the tray isn't dry, then I don't add any more water.

Paul4444
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Yes that's the cells I'm using. When I first start the soil is higher but seems to sink after a while. How dry do you let them get, it's quite hard to test the depth of the moisture as my fingers are too big to check properly without disturbing the seedlings. Any tips?

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digitS'
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My plant starts are bottom watered for about their first 4 to 6 weeks. I'm reluctant to get to the sprinkler can or watering wand but finally, it seems necessary.

My decision on when to set a flat into the basin is based partly on what the soil surface looks like. More importantly, it's the weight of the flat that prompts it. I decided that experience and by-guess & by-golly might be just a little too casual to try to explain it. So, I got out a scale to weigh 'em.

Different plants have different needs and different stages of growth are likely to change the requirements. Perhaps, there is a difference in potting soil ...

Anyway, I weighed 4 thoroughly soaked trays, just out of their 2nd watering after the seedlings had been moved to 4-packs, 48 to a flat. Then, weighed them when I thought that they should go back in the basin. The flat had lost right at 50% of its weight.

In other words, if the soil was saturated but no longer dripping and the container weighed 8#, my judgment was that when it weighed 4# -- it should go back in the water.

Steve

Paul4444
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Thanks I'll give that a try. Back to my problem with the soaking soil. Would my best bet be to not let the water reach the surface before I stop watering? How close do you guys put the fan?

imafan26
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The fan is for air circulation, it is not the problem. You should not have to flood the tray until the water reaches the top of the cells. A 1/4 inch of water should still be enough to wick up to the top of the cells as long as the soil is not bone dry.

The fan should not be so close or set so high that the top of the cells dry out much faster than the bottom.

Paul4444
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Sorry for the confusion but I don't flood the tray. I use a separate tray form the one the seedlings are growing on that has raised ridges, about 1/8 inch high, and add water until it is just touching the drainage holes. When the surface becomes wet the cells are moved back to the tray that they are growing on under the lights. As my seeds germinated at different times the flat has been separated into the individual 6 cells and these are water separately when needed. I wonder if when I'm placing just 1 of the 6 cells in the flat and fill it to just the drainage holes that this may be too much water, as opposed to when a full flat is put in there and the water just filled to drainage holes as the water will be taken up by lots of cells rather than just 6 (does this make sense?).

Also with the previous comment that the soil level may be too low and the seeds shaded, should risk cutting the cells down so that the soil is at the top?

Thanks

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applestar
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Don't cut the cells. You want MORE soilmix. For most seedlings, you can pile on more soil mix -- up to just below seedleaves. Tomatoes particularly, but others too. And lettuce and cabbage need this treatment to keep from flopping over when they cat top heavy. In fact I have started doing this deliberately for tomatoes when lighting situation us less than optimal.

I think the loose, unpacked soilmix is drying out too quickly but also wicking up to the top too quickly -- next time do one of the things mentioned above.

To add the mix, use moistened but drying mix and use a spoon or a makeshift chute/funnel. I use one of those restaurant sever's tablecloth sweepers.

Paul4444
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Thanks I'll give that a try tonight. Thank you all for your help, this is a learning experience for me and you're all making life much easier. I posted a similar question on another forum the day before this and still haven't had a single reply. I understand it can get boring answering obvious novice questions but I assure you it is appreciated.

I'm still unsure why the soilmix will be drying out and wicking up too quickly. Was it how I prepared it in the beginning? I lightly moistened it in a bucket and mixed it around before pressing down in to the cells.

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digitS'
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Different soils have different properties.

I'm risk-averse when it comes to seed starting. I've used Black Gold organic potting soil for decades ... well, since the organic became available but the standard, before that. It is just that it has always done a good job for me. I'm not even using a sterile starter mix. What I've been doing just ain't broke.

Using a greenhouse rather than growing indoors under lights must also be quite different. Small or large changes would be a whole new ball game ... before I get into too many metaphors, I'd better stop but don't worry about "obvious" questions, Paul. There's a bigger world out there beyond a few potted plants that each one of us is trying to care for.

Steve

Paul4444
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Thanks. Two maybe last questions. I'm using t5ho lights and there seems to be some disagreement online as to the distance from the seedlings. Some say 1-2 inches and others disagree saying up to 6 inches. Does anybody here have experience?

Also if someone has time could you please post a pic of your starter mix in a cell after its been watered so I can compare it to mine (with little experience I may be misjudging what is wet and what is moist).

Thanks

Paul

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applestar
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I think T5's run hot and 1" is too close, 2" is probably as close as I want to get. 6 inches is too far and about 4" is about maximum distance I would allow unless there are other strong light sources to compensate or unless I'm using the light for low light tolerant seedlings.

Paul4444
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Thanks. How do people pre-wet their mix. I use promix starter mix and I was just slight dampening it in a bucket but I've read that some people get it so you squeeze it like a damp sponge and a little water comes out then leave it overnight. I wonder if this is my problem with wicking too much and the soil level decreasing (compacting). Any thoughts?

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digitS'
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I soak the filled containers for an hour or two,

allow them to drip overnight,

then sow seed on the surface,

covering it with soil mix straight from the bag.

Steve



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