Why Seeds Do Not Germinate | Reasons for Seeds Not Germinating or Sprouting

Sometimes, seeds fail to germinate or sprout once planted in soil, despite our best efforts. Know the reasons why your seeds are not germinating or sprouting. Your seeds fail to germinate because of some common mistakes you may be doing while germinating seeds. Understanding the reasons behind seeds not germinating or sprouting is important for gardeners.

Seed germination depends on various factors, including seed quality, seed dormancy mechanism, soil quality, temperature, moisture levels and weather. Your seeds not germinating or sprouting may be doing some fatal mistakes.

Reasons Why Seeds Fail to Germinate

Coriander Seeds Germination
Germinated Coriander Seeds

Let's look into some common mistakes you may be doing so your seeds may not germinate in soil. In many cases, you may replant seeds that did not germinate, provided they are still viable (see below). Learn the following reasons for your seeds didn't sprout or  germinate.

1. Poor Seed Quality

One of the primary reasons for seed germination failure is poor seed quality. Seeds that are old, damaged, or improperly stored may lose their viability and ability to germinate.

It is essential to buy seeds from reputable garden shops and ensure they are fresh. Always check the expiry date on the seed packet.

Always store seeds in a dry place or in air-tight bottles or packets to maintain their viability. Seeds will lose their viability if stored in humid environment.

If you are collecting seeds from your plants, then ensure that the fruit or seed pods are fully ripe before collecting seeds, as I always do in Sydney, Australia. Seeds from a green tomato will not germinate, but seeds from the red tomato will germinate easily.

Some seeds like neem, mango, etc. need to be as fresh as possible for germination, while other seeds like coriander, tomato, beans, etc. have a longer shelf life and get germinated even if they are old.

How to Check Seeds Viability

1. Soaking method: Simply put the seeds in water for 5-10 minutes in a glass, if the seeds float, then they are not viable. Discard these floating seeds, they will not germinate. Plant only those seeds which sink in water.

2. Paper Towel method: Wrap the seeds in a wet kitchen or toilet paper and keep it in a polythene bag or Ziploc bag to germinate them quickly (how germinate seeds in paper towel).

2. Seed Dormancy

Some seeds remain dormant until certain conditions are met. Factors such as temperature, light exposure, or exposure to specific chemicals may break seed dormancy and trigger germination.

Seeds of plums, nectarines, peaches, persimmon, etc. are needed to be stratified to break their dormancy.

Seeds of some fruits like custard apples, plums, nectarines, apricots and peaches etc. are enclosed in hard shells. It is better to take them out from their pits before trying to germinate them.

3. Infected Pots and Trays

If you use old pots for sowing seeds, the chances are that they are infected with mold and fungal infections.

You should always clean your old containers with soap or baking soda or or a dilute solution of bleach or hydrogen peroxide.

4. Poor Soil Quality

Soil quality is very crucial that can affect seed germination. Good aeriation is needed in soil for successful germination. The aeriation allows soil to have enough oxygen needed along with moisture to breakdown and mobilize the compounds in seed to germinate.

Seeds require free-draining soil with the right balance of nutrients and pH levels to sprout.

The garden soil may be compacted or containing stones, wood chips, large chunk of solid soil, that can prevent the seeds from sprouting.

Also waterlogged soil can prevent seeds germinating. You can add some coarse river sand or perlite in the soil to make it good-draining.

The soil may contain harmful microbes that can affect seed germination. If you suspect that your soil contains harmful pathogens, then leave your soil in sun for a few days before using it for germination.

The soil may also contain substances like allelopathic chemicals released by other plants or residues from fertilizers or pesticides, that may inhibit seed germination. It is better to conduct soil tests to improve the chances of successful seed germination.

You can amend the soil as needed before planting to create optimal conditions for seed germination.

You can buy seed raising soil mix or seed starting coco peat pellets from a garden shop or make your own by mixing some cocopeat, river sand and compost in the soil.

5. Incorrect Planting Depth

Correct planting depth is critical for seed germination. Seeds need to be planted at the appropriate depth to receive the right amount of moisture, warmth, and oxygen for germination to occur. Planting seeds too deep or too shallow can hinder their ability to sprout.

Seeds planted too deep in the soil do not germinate because they are unable to get sufficient oxygen needed for germination.

So what is the ideal depth for sowing seeds? It is better to follow recommended guidelines for each seed. As a rule, plant your seeds at a depth equal to two or three times their width. Some seeds are very tiny, they are just left on the surface of soil to sprout.

6. Incorrect Temperature and Moisture Levels: Wrong Season

The temperature and moisture are two important factors for seed germination, as seeds have specific temperature and moisture requirements for sprouting. Planting seeds during too high or too low temperatures can inhibit germination.

Most seeds germinate ideally at day time temperatures 18 - 21°C (65 - 70°F) and the nighttime temperature as low as 12°C (54°F). Leafy vegetables and root vegetables prefer lower temperature, no more than 18°C (65°F) during the day and 5°C (40°F) at night.

A higher temperature may increase evaporation and decrease moisture, which will affect germination.

Seeds will not germinate in cold weather because low temperature can slow down or delay the the metabolic processes that are necessary for germination. That is why seeds will not germinate in refrigerator. 

However, many seeds require a period of cold temperatures in fridge, known as stratification to break their dormancy cycle, even they may germinate during stratification (growing apricot from seeds).

Apricot Seed Germinated in Fridge during stratification
Apricot Seed Germinated in Fridge during stratification

It is therefore essential to plant seeds in the right season depending on the Zone you live in.

You can use a heat mat which keeps steady heat at all times and encourage fast germination.

7. Incorrect Watering

Similarly, excessive or inadequate moisture levels in the soil can prevent seeds from sprouting.

It is important to ensure consistent moisture levels for successful germination. If the soil is too dry, they fail to sprout; and if it is too wet, the seeds may rot in soil. Keep the soil damp but not soggy.

The seeds fail to germinate in waterlogged soil, because the oxygen dissolved in water does not enters the seed due to excessive water.

You can cover the pot with a transparent polythene sheet to contain moisture in the soil.

Capsicum Seedlings
Capsicum Seedlings

Young seedlings can die due to improper watering (how to grow capsicum, bell pepper from seeds). You can water using a bottom tray method. In this method of watering, place the pot on a try and fill it with water and do not water from top. When the soil becomes dry, it will absorb water through the drainage holes of the pot.

8. Light Requirement

Most seeds do not need light for germination, and they can germinate in complete darkness.

Seeds Needing Light to Germinate

Some seeds need light to germinate and will fail to germinate if they are not exposed to light.

These seeds are, in general small in size - smaller than 6mm need at least 8 hours of light to germinate. Light needing seeds for germination include Begonia, Chamomile, Coleus, Dill, Ficus, Impatiens, Lettuce, Lavender, Lemon balm, Lettuce, Marjoram, Oregano, Petunia, Poppy, Primrose, Rosemary, Savory, Strawflower, etc.

Some of the seeds needing light to germinate are almost dust-like. Do not not cover the seeds which do not need light to sprout with soil, but simply press them into moist soil when you sow them, a very thin covering of soil would place them in the dark.

Tiny seeds have limited food reserves because of their small size, so require light to break seed dormancy to germinate. 

There are some exceptions. Seeds such as tomato and onion are quite small but they need darkness to germinate. So, they should be covered with a thin layer of soil to prevent light during germination.

Light Independent Seeds

Majority of the seeds are light independent. These seeds will germinate with or without exposure to light, but expose them to light after they germinate.

Seeds Needing Darkness to Germinate

Medium and large seeds, in general, need darkness for germination. Some of these seeds need darkness to germinate while others prefers darkness but can germinate both in light and darkness.

Seeds that only germinate in darkness are mostly very large, about 1 inch in size. These seeds need to be planted about 2 inch deep in soil, so no light will reach them and you can place their pots in a lighted spot for germination. The seed that require darkness to germinate reduces the production of germination-stimulating enzymes in the presences of light, so they need darkness.

Here are some seeds that need darkness to germinate: Borage, Calendula, Gazania, Nasturtium, Sweet pea.

Sow the following seeds either on surface or cover them very lightly in soil and then place in the dark to germinate: Butterfly flower, Coriander, Pansy, Phacelia, Phlox, Verbena, etc.

By understanding the above factors and taking appropriate measures to proper seed selection, soil preparation and environmental management will ensure seed germination and nurturing them into thriving plants.