Why Did My Seedlings Stop Growing?

Why Did My Seedlings Stop Growing?

When we start seeds indoors, we are trying to give them a head start before putting them into the harsh world of the out-of-doors. So, when our tender, baby seedlings seem to just pause, or stall in their growth, it can be very stressful.

What does “seedling stall” look like?

Seed stall is when a seedling that spouted stops producing new growth. With tomatoes, for instance, it can look like the tomato sprouted it’s seed leaves (the first two leaves) and then nothing happens after that for at least a week. It can also happen later, after some true leaves have sprouted, and then the plant just seems frozen in time. Alive, but “stuck” at that same stage. Sometimes you will also see signs of a nutrient deficiency like purple or yellow discoloration of the leaves or stem.

Why did my seedlings stop growing?

Seedlings start out using the food that’s contained within their own seed. That’s what produces the initial roots, stem, and leaves. After that, the plant starts to rely on the outside world for it’s continued growth: nutrients it would find in soil. If you are growing in a “soilless” medium, like a seed-starting mix, the plants will have little to no nutrients to use for fuel. Some seed starting mixes will contain some basic nutrition for seedlings to get you through the early growing processes, but not all do. Also, overwatering can wash away nutrients, making them unavailable for the plants.

Two newly-emerged tomato seedlings
Two just-emerged tomato seedlings. If they stay like this with no new growth for over a week, then they have stalled.

My seedlings are stalled, what do I do?

You’ve got two choices, based on the current size of your seedlings.

  1. Transplant the stalled seedlings into a growing medium with compost or fertilizer, like a potting mix. This works best for plants that have some true leaves or like to be repotted, like tomatoes. I love to use Formula 420 Potting Soil . I swear the seedlings double in size over night!
  2. Add some diluted fertilizer to the soilless mix the seedlings are in. This will give them some nutrition to help keep them growing. This method works well for either seedlings with only seed leaves or ones with some true leaves.

Keep an eye on your plants, and note changes after you apply your chosen method to make sure they have started to recover.

How do I know I’ve fixed the problem?

Once the seedlings have access to the right nutrition, they should start growing again. You should see new growth, and any discoloration should fade. Taking pictures daily will help you to see this process as it occurs, since you might not notice changes just by checking every day.

Tomato seedlings showing new growth beyond the seed leaves. Now it’s time to thin them out!

What if those options do not help?

Now we’re into less simple territory. I would check for any of these other, less likely possibilities:

  • Insects on your seedlings, like aphids or mites, that drink the juice of the seedlings, sapping their strength
  • Too much chlorination in your tap water. This is unlikely, but some plants are more sensitive to chlorine. If you think this is the issue, you do not need to purchase distilled water or collect rainwater for your seedlings. You can leave tap water out in an open container for about 3 days and the chlorine will off-gas and the water will be safe.
  • Overcrowding or too small of a container can cause roots to run out of space and halt growth. In the image above, you can see that while both seedlings are growing well, only one should be occupying that cell. Thinning or repotting can help with this issue.

How can I make sure my seedlings never stall again?

I used to have this problem every year when I made my own seed starting mix. Now, I have been taking the easy route and using a pre-mixed seed starting mix, and I can get at least 4 true leaves on a healthy tomato plant without any stall, great size for its first potting-up.

I have had great luck with this one I picked up at my local hardware store: Whitney Farms Organic Seed Starting Mix

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