What happens when a seed germinates? Learn about the magic of seed germination, the process of a seed swelling and rupturing what we call sprouting , and how to identify all the different parts of a seed and seedling. By understanding seed anatomy and the science behind germination, you'll be better equipped to troubleshoot common seed starting problems.
The anatomy of a seed and seedling is something every gardener should know, and learning the science behind it will help you become a better gardener! Try raising them from seed, where it may take a few tries and a few rounds of natural selection before you get the perfect plant. Seed coats can be soft and thin like beans or fleshy and thick like squash. Think of them as armor for the future plants inside; the seed coats protect against the elements until conditions present themselves in just the right manner for germination to take place.
Seed coats are adapted to their environments, and they function as a barrier to damage or injury, heat or cold, bacteria or fungi, and even stomach acidity if ingested by animals. Soaking your seeds first can help with this, or in the case of tomato seeds, you can ferment them to speed up germination.
On some seeds, you can see the scar, or hilum, that was left behind when the seed became detached from the mother plant similar to a human belly button. Hilum are most visible on bean seeds, where the scars as known as eyes—as in black-eyed peas. Others are less noticeable and look like little nubs or dents on the seed coat. Inside the seed coat is the embryo baby plant , the endosperm nutritive tissue , the cotyledons leaf-like structures , and the beginnings of the root and shoot.
They are just waiting to be released! Germination occurs when all the proper variables are in place for that particular variety oxygen, temperature, light or darkness and the seed coat absorbs water, causing it to swell and rupture. The first sign of life comes from the radicle, a little white tail that eventually becomes the primary root of the plant.
The role of the radicle is to anchor the plant in the ground and start absorbing water. Once it absorbs water, a rudimentary stem emerges and the cotyledons start to unfurl, often taking the seed coat with them as they rise above the soil. Cotyledons look like leaves but are actually not leaves at all. There can be just one cotyledon monocotyledon, as is the case with onions and corn or there can be two dicotyledons, which are the majority of your vegetables.
The cotyledons feed the plant until all the nutrients are used up. You can see how these two varieties of tomatoes have the same cotyledons, but once their true leaves emerge, one seedling has the serrated edges typical of a regular tomato leaf while the other has the smoother lines of a potato leaf. In general, it takes one to three weeks for true leaves to appear once the cotyledons emerge. The timeframe is dependent on the type of plant, as well as environmental factors like sunlight, moisture, and temperature.
Cotyledons are always the first leaf-like structures to form when a seed germinates. Most cotyledons are nondescript and tend to look similar within a plant family.
For example, tomato, pepper, and eggplant seedlings members of the nightshade family all start out with a pair of long, narrow leaves with slightly pointed tips. On the other hand, radishes, broccoli, and kale members of the brassica family begin life with two stubby, heart-shaped cotyledons. Once the true leaves develop, they start to resemble actual leaves on the mature plant—just tinier versions of them.
True leaves grow above the cotyledons and take over the job of supporting the plant for the rest of its lifecycle. To do this, gently press the soil medium to create a firm surface. Then, place the seed on top of the medium and gently press down, making sure the seed is still exposed.
There is no benefit to a tough-love approach with seedlings when they are young. They will either instantly die or become weak and then fail to thrive. Even the most stalwart plants, when young, need a considerable amount of coddling and attention.
When your seedlings are large enough to plant outdoors, you need to prepare them for the transition by hardening off. The hardening-off process is simple, though it can be time-consuming; it involves exposing your plants to the elements gradually. The first day of hardening off, place your seedlings outdoors for one hour, and then bring them back indoors. Gradually increase the amount of outdoor time every day for 6 to 10 days.
You will need to make some judgment calls based on the outdoor temperature and the fragility of your seedlings. If it is a particularly cool day or very rainy, you will want to decrease the time of that hardening-off session. When sowing seeds, begin modestly if you are a beginner. If you sow more seeds than you can reasonably maintain, it will become challenging to nurture the seedlings into adulthood. Depending on the type of plant you want to grow, you might be able to direct-sow seeds in outdoor containers or in the ground when outdoor temperatures warm up.
For seeds to germinate, most must be kept warm: about 65 to 75 degrees Fahrenheit. A favorite place to keep seeds warm in order to germinate is on top of the refrigerator.
Or, you can purchase seed-warming mats to place under the seed trays. Once a seedling emerges, they can tolerate fluctuating temperatures within reason.
Whatever type of light you use, natural or artificial, make sure it produces enough heat to keep the plants in the to degree range. To be able to identify seedlings as they grow and to know when they will be ready for transplanting, you should label the seed containers as you are sowing. For every type of seed sown, use popsicle sticks or plastic plant markers and permanent ink pens to record the plant name and date sown. Insert the plant labels into the soil near the edge of the container or tray.
Starting seeds can be a difficult process. However, one of the most satisfying benefits of this labor of love is eating a garden-grown tomato or marveling at the flowers that you nurtured from day one. Growing plants from seed takes dedication, attention, and time. Recognize that you might make mistakes along the way, but you should not give up. The results outweigh the challenges along the way.
Thanks, Bret! Why would you grow your own seedlings rather than buy them from a professional grower? There are a few advantages:. But with this guide, I aim to make it less so! As with most gardening activities, seedling success has a lot to do with timing. Start your plants too early, and an unexpected frost might kill them. Start them too late, and they may not have enough time to mature.
Fortunately, seeds often come with planting schedules stamped on their packet see the picture above for an example. Cultivating healthy seedlings requires only a few things. You can order high-quality seeds online or from seed catalogs. But local garden shops and seed swaps are also great sources. A key benefit of buying online is that you can often see product reviews from other gardeners, which may give you an idea of what to expect.
Many gardeners, myself included, find that soaking seeds overnight in a shallow bowl of water improves and speeds germination rates. And this seems to work for most plants. Before you plant your seeds, thoroughly soak your rockwool cubes for half an hour or so. Then plant the appropriate number of seeds based on crop type:.
For smaller seeds, fill the hole only half-full. This will ensure seeds have enough moisture to germinate. Tower Tip: Not all seeds must be sprouted before being transplanted. Some you can seed directly into your Tower Garden. These include plants that grow very quickly after germinating, such as beans, cucumber, and squash.
Before your seeds sprout, temperature is a critical factor. But fruiting crops usually prefer the upper end of that range. If your propagation area is cooler than that, a heating mat may help. Also consider covering your seedling tray with the dome or plastic wrap until the seeds sprout. This helps create a warm, humid microclimate.
Too much humidity for too long can breed fungal pathogens. Essentially, you want your rockwool cubes to stay moist but not oversaturated. Adding about a quarter inch of fresh water replacing any existing water to the seedling tray daily should do the trick.
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