Germinating Seeds and Caring for Seedlings

By Kyle Ladenburger
Published: January 26, 2021 | Last updated: August 4, 2022 06:14:05
Key Takeaways

Within each seed is all of the genetic information needed to grow a mature plant destined to create life-sustaining fruits, grains or maybe just oxygen. But to begin its life as a growing plant, that little seedling requires some help to germinate.

Source: Vaivirga/Shutterstock

At first glance, a seed appears to be just a small, simple little thing, but hidden inside is pure potential – the potential to grow into a beautiful, mature plant that can host beautiful flowers and delicious fruits.


Many of the foods we eat to survive and the medicines we take to stay healthy come from plants that got their humble starts as seeds.

How Seeds Work

Inside that simple-looking seed exists all of the genetic information needed for that plant to grow throughout its entire life cycle. Whether a certain plant is destined to create fruits, grains or maybe just oxygen, its destiny is retained inside that little seed.


Once a seed germinates, sprouts and begins to grow, nature kicks into gear and life-sustaining processes within the plant begin. But for a seed to begin its life as a growing plant it will require a little help.

The seeds of flowering plants (angiosperms) are placed into two distinctive categories: monocotyledons (monocots) and dicotyledons (dicots). This classification is based on one specific characteristic of a seedling.

Cotyledons are the first leaves that an infant plant will grow and they will act as a food source for the seedling until the emergence of the first true leaves, when the plant begins the process of photosynthesis to provide itself with carbohydrates for energy.


Monocots are classified as such because they only have one cotyledon (seed leaf) while dicots have two. Plant seeds classified as monocots include wheat, corn, sugar cane, and bamboo. Seeds classified as dicots include beans, tomatoes, peppers, and cucumbers.


A seed is essentially made up of three parts: the seed embryo, which is basically a baby plant that will grow and mature under favorable conditions, the endosperm that will supply the initial food and energy source for the growing embryo, and the seed coat – the hard outer shell that protects the seed until it is ready to grow.

Germination is the process in which a seed and its embryo go from a dormant state to an active, growing state. Successful seed germination is dependent on certain conditions being met. These conditions are both internal and external and can vary from seed to seed. The external conditions that are most crucial are water, temperature, oxygen and, with certain seeds, even light or darkness.

Water and Seeds

Watering Seedlings with Spray BottleWater is essential because a mature seed is often quite dry. Seeds take in water through a process called imbibition. As water accumulates in the seed, it causes the seed coat to swell and break apart. Water also activates the breaking down of the endosperm, chemically converting it into a useable food source.

Temperature and Seeds

Temperature has an effect on the metabolism and growth rate of cells within the seed's embryo. Seeds usually have a temperature range in which they will germinate and germination won’t likely occur above or below this range.

For most seeds, this range is between 60 and 80°F, but some can germinate in soil temperatures as low as 40°F. Oxygen is required for proper seed germination. In gas form, oxygen will reside in soil pore spaces and assist in the development of a much-needed root system. If the seed is planted too deep or if the soil becomes too waterlogged, the seed may not germinate.

Should I Start Seeds Indoors or Outdoors?

Spreading Seeds in Germination TraySpreading Seeds into Germination Tray. Source: Ilike/Shutterstock
When germinating seeds at home or in a greenhouse the first thing to think about is whether or not a certain seed should be started and transplanted to another location or if it should be directly sown into its permanent home, whether that is in soil or a growing medium. Plants like radishes and carrots should not be started indoors and transplanted at a later date, as this may result in disrupted growth that can lead to unfavorable results.

However, starting tomatoes, peppers and cucumber seeds, just to name a few, indoors is a great way to get an early jump on the outdoor growing season or for an indoor garden. When choosing a medium to germinate the seeds, look for one that includes words such as seed starting mix. This type of growing medium will likely have a moderate elemental fertilizer charge that will benefit newly sprouted seedlings.

Seeds can be germinated in many different styles of trays and containers, so choose the type that best fits the project at hand. If starting just a few seeds, a simple, flat starting tray will work. When planting many seeds at once, it may be wise to use trays that are divided into separate growing chambers to cut down on the amount of transplanting needed as the plants grow.

Remember, most seeds will germinate at average room temperature, but some growers do use heat pads underneath the starting trays.

Read also:

Seed Germinating Tips and Tricks

The added warmth in the growing medium can speed up the germination process, but for most seeds, it is not necessary. Using supplemental lighting, like a T5 fluorescent bulb, can also help provide extra heat.

Though seeds may not need light to germinate, the coming seedling will surely need light, so having a light source ready to go is a good idea. I would advise against starting seeds in a bright windowsill because the glass can alter the intensity of the sunlight and the plants may stretch and become leggy.

I suggest lightly moistening the growing medium before planting any seeds. This will help to ensure that the medium is not over-saturated or waterlogged and that the moisture is spread evenly throughout. Using the eraser side of a pencil or the tip of your pinky finger, carefully make small divots in the medium at the desired planting depth.

Many plants require a depth of around one-quarter inch, but to find the correct planting depth for the type of seed being grown, consult the back of the seed package – in my experience, these suggested planting depths are accurate and not following them can result in lower germination rates. If planting in a flat starting tray, space seeds at least an inch apart either in rows or in a grid pattern.

Gently place one or two seeds in each divot, cover lightly with growing medium – oxygen is important during germination, so don’t pack the medium down too much – and spray the entire tray lightly with a hand-held water mister.

A pre-moistened soil should stay wet long enough for the seeds to germinate, but it may need to be sprayed with the mister occasionally to maintain even distribution of moisture.

Some growers use starting trays that have plastic hood-type lids. This will keep the humidity around the seeds at higher-than-average room levels and may help increase the chance of successful germination. Be sure to check the seeds on a near daily basis to maintain an optimal environment.

As the seedlings begin to pop up through the soil there are a few environmental aspects that should be given proper attention right away: light intensity, humidity and airflow. Seeds from different plants will germinate in different lengths of time, so check the seed package for estimated germination times to know when to be ready.

Lighting, Humidity, and Airflow During Germination

Seedling Under a T5 Grow LightTomato plant under T5 grow lights. Source: Southern Exposure/Shutterstock
Many seeds can sprout in total darkness, but once that plant breaches the soil, a sufficient light source is imperative. Those first true leaves will need a light source to perform photosynthesis and create the carbohydrates to sustain both normal plant growth and, most importantly, root growth.

Without proper lighting the early vegetative growth of a plant can be negatively affected and this could cause long lasting problems that may result in a lower yield. Humidity can be helpful during the initial germination process but as the little seedlings begin to grow, high levels of humidity can spell disaster.

As internal processes burn up the seedling's energy sources, the plant will need to release oxygen as a gas through its stomata in a process that is called transpiration.

As the oxygen leaves the plant, water and elemental nutrients are pulled up through the roots. In a humid environment, the stomata will remain closed and the roots will not take in water. If the growing medium is moist, as it most likely will be, the water will have nowhere to go and the roots will likely suffocate and die. Airflow and humidity almost go hand in hand.

A nice flow of air through the plant's canopy will encourage the flow of carbon dioxide to the leaves and, subsequently, oxygen away from the leaves, which is important for plants in all stages of growth. A small fan on medium or low can help keep humidity levels low and the heat from any supplemental lighting to a minimum.

Watering Seedlings

As for watering practices, be sure to keep the rooting medium moist but not too wet. Seedlings need water and going too long without can result in serious damage but if the medium remains too wet for too long it may impair root growth.

As the seedlings grow they will eventually exhaust any nutrient charge that the growing medium had to offer, so light fertilization with a nitrogen-based fertilizer may be needed while waiting to transplant into a different or permanent container.

So, day by day, as the seedlings grow, given proper care and attention, they inch closer and closer to fulfilling their own unique destiny.

And as we stand by, eagerly awaiting the literal fruits of our labor, it is important to remember that every plant we grow has entered into this life as a small, almost insignificant looking thing that so many people refer to as simply, just a seed.


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Written by Kyle Ladenburger | Director of Regulatory Affairs for Age Old Organics & ENP Turf, Freelance Garden Writer

Profile Picture of Kyle Ladenburger
Kyle L. Ladenburger is a freelance garden writer who has worked in the gardening/hydroponics industry for over 15 years. As an avid indoor and outdoor gardener he is well versed in nearly all types of growing methods with an overall focus on sustainability and maintaining healthy soils. He holds a strong conviction that growing one’s own food is a powerful way to change our lives and our world for the better.

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