Seeds Not Germinating? 5 Common Reasons Why

September 18, 2020

📚 Part of the Living Towers Seeds & Seedlings Guide
This article is part of our complete collection of guides to help you start seeds successfully and grow strong, healthy seedlings.

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Your seeds aren't germinating. Now what? Before assuming the seeds are bad, take a look at the conditions around them. Seeds need the right combination of moisture, oxygen and temperature to germinate successfully.

Seed-starting problems are especially noticeable when growing for a Tower Garden. Instead of scattering many seeds across a garden bed, you're usually starting individual plants in rockwool cubes. When one seed doesn't sprout, you're left with an empty growing spot.

If your seeds haven't sprouted, these are the most common reasons why — and what you can check before starting again.

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Troubleshooting a germination problem? Start with the factor most likely to be causing it.

Too Much or Too Little Water Not Enough Oxygen Wrong Temperature Old or Poor-Quality Seeds Needs More Time Quick Troubleshooting

1. The Seeds Are Too Wet or Too Dry

Seeds need moisture to begin germination. A dry seed is dormant. Once it absorbs water, the seed begins the process that eventually causes the seed coat to split and the young plant to emerge.

But more water isn't necessarily better. Rockwool should remain moist while seeds are germinating, not completely saturated or sitting deep in water.

When starting seeds in rockwool

About 1/4 inch of water in the bottom of the seed-starting container in the morning is generally plenty. You can also add water from above during the day when needed. The goal is to keep the rockwool consistently moist without leaving it swimming in water.

2. The Seeds Aren't Getting Enough Oxygen

Seeds also need oxygen during germination. When rockwool stays excessively wet, the air spaces within it can remain filled with water, reducing the oxygen available around the seed.

This is another reason not to completely submerge your rockwool cubes. Keeping them moist rather than waterlogged provides the seed with both the moisture and oxygen it needs.

3. The Germination Temperature Is Too Hot or Too Cold

Temperature is one of the biggest reasons seeds fail to germinate. Different crops germinate best at different temperatures, so conditions that work perfectly for one seed may be unsuitable for another.

For many crops, germination occurs well around 65–75°F, but there are important exceptions.

Lettuce

Lettuce prefers cooler germination conditions and germinates well around 65°F. Very high temperatures can inhibit lettuce germination, which is one reason lettuce can become more difficult to start during summer.

Spinach

Spinach also prefers cooler conditions. Here in South Florida, summer temperatures make spinach germination difficult enough that we don't grow spinach seedlings during the hottest part of the year.

Peppers

Peppers prefer warmer germination temperatures and can germinate poorly or very slowly when conditions are too cool.

Eggplant

Like peppers, eggplant prefers warmer conditions, around 80°F, and may struggle to germinate when the growing medium is too cool.

Always check the germination information for the specific crop you're planting. If your rockwool is much warmer or colder than that crop prefers, temperature may be the reason nothing is sprouting.

4. The Seeds Are Old or Have Lost Viability

Sometimes your growing conditions are fine and the problem really is the seed.

Seed viability gradually declines over time. How quickly that happens varies by crop and by how the seed has been stored. Heat and humidity can shorten the usable life of seeds considerably.

Seeds stored in a hot garage or shed through summer, for example, may lose viability much faster than seeds kept cool and dry.

Use fresh seed whenever possible.
Keep leftover seeds cool and dry.
Store seeds in an airtight container to protect them from humidity.
Don't assume the printed date is the only factor — storage conditions matter too.

5. The Seed May Simply Need More Time

Not every seed germinates at the same speed. Some crops emerge quickly, while others naturally take longer — and cooler-than-ideal conditions can slow germination even further.

Before starting over, check the expected germination time for the variety you're growing. If you're still within the normal germination window, the seed may simply need a little longer.

Why Aren't My Seeds Germinating? Quick Troubleshooting Guide

What You're Seeing	Possible Cause	What to Check
No seeds germinated	Temperature, moisture or seed viability	Check rockwool temperature, moisture level and the age or storage history of the seeds.
Only a few seeds germinated	Reduced seed viability or inconsistent conditions	Check seed age, storage conditions and whether all cubes are receiving similar moisture and temperature.
Rockwool is soaking wet	Too much water and reduced oxygen	Don't leave the cubes submerged. Keep the rockwool moist rather than waterlogged.
Rockwool keeps drying out	Not enough moisture	Check the cubes more frequently and maintain consistent moisture while seeds germinate.
Lettuce or spinach won't sprout in summer	Rockwool may be too warm	Move the seed-starting setup to a cooler location and check the preferred germination temperature for the variety.
Peppers or eggplant are very slow	Rockwool may be too cool	These warm-season crops generally prefer warmer conditions for germination.

Starting seeds specifically for a Tower Garden?

Germination is only the first step. Our How to Grow the Perfect Seedling guide walks through preparing rockwool, planting, watering, lighting, feeding and getting seedlings ready for your Tower Garden.

Prefer to Skip Seed Starting?

If germinating your own seeds isn't for you, we grow more than 100 varieties of live seedlings ready to plant in your Tower Garden or other growing system.

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