Why is germination necessary

Seeds come in all shapes and sizes. Some tropical rainforest orchids have seeds that are smaller than a pinhead—so small,in fact, that they are like dust. At the other end of the scale is the enormous Coco de Mer seed which can be up to 40 centimetres long and weigh as much as 18 kilograms, about the same weight as a medium-sized dog! In flowering plants, seeds develop in a fruit.

The fruit protects seeds but also helps with their dispersal from one place to another. Sometimes the fruit is nice and soft and delicious, like a berry that attracts animals who then accidently carry the seed to a new home. Other times the fruits are hard and woody, like those of a banksia or eucalypt. This is the Svalbard Global Seed Vault—a seed bank established by the Norwegian government which holds copies of more than 4, plant species from seed banks around the world.

The vault holds over 4, plant species including essential food crops such as beans, wheat and rice. The northernmost place in the world with its own airport, Svalbard is the perfect place for the seeds to be delivered from around the world for cold storage. Even if the power fails, the ambient temperature on this chilly island 1, kilometres beyond the Arctic Circle will keep the seeds frozen without extra cooling.

In fact, experiments show that some of the tissues inside of seeds remain active, and even carry out some basic metabolic processes, such as cellular respiration GLOSSARY respiration a chemical process whereby energy is released from glucose. The embryo gets energy by breaking down its food stores. During aerobic respiration:.

Seeds need the right temperature to germinate, and this varies depending on the species of plant and its environment. Some need fluctuations in temperature. Some need very cold conditions for a few weeks or even months before they will germinate at a higher temperature. This ensures that cold climate seeds, for example, delay germination until after winter. What about light, you might wonder? Such seeds can lie dormant for years, until, say, a tree falls, opening up a gap in the forest canopy and exposing the seed to light.

Interactive How seeds germinate 1 Next Reset. Nearly all seeds are in a sort of suspended animation, called dormancy, until conditions are just right for them to germinate. Dormancy means that, even when exposed to water, oxygen and the right temperature, a seed may delay germination until it gets certain other environmental and chemical cues.

A seed may be dormant while still on the parent plant this is known as primary dormancy , or it may become dormant after it has left the parent plant secondary dormancy. It allows seeds to delay germination until, for example, temperatures are just right for the seedling to thrive. It also means that seeds can wait to become seedlings until they are at a distance from the parent plant for example, by being eaten by animals and excreted elsewhere , which reduces competition with other seeds from the same parent.

Dormancy happens through a few different kinds of mechanisms, some of which happen outside the embryo exogenous dormancy , others inside it physiological dormancy. An example of an exogenous dormancy mechanism is a hard seed coat, which stops the seed absorbing water, and sometimes air.

Dormancy may also be triggered by factors inside the embryo, especially chemical changes, which need to occur in the seed before it will germinate. Some seeds, for example, need a period of light or dark to germinate.

People working in the agricultural industry will often carry out processes that imitate these natural ones in order to break dormancy and get seeds to germinate—for instance, by chilling seeds to imitate cold weather or by applying abrasives to weaken the seed coat. How long can a seed survive? Most seeds seem to be able to live in the soil for between 10 to 15 years.

But the lifespans of seeds vary enormously. The seeds of some annual grasses need to germinate within a few weeks, while those of other plants may slumber for hundreds of years. The Arctic lupin holds the record so far. Seeds of this plant were found in the burrows of lemmings in Alaska. Researchers were able to germinate the seeds—which had been buried in the Arctic soil since the end of the last Ice Age—and produce plants.

We need to help supply the nutrients and vitamins for the plant to have what it needs to grow strong and reach its full yield potential. As we plant the seeds in the ground we have high hopes of a plentiful harvest.

This is the reason that we pick great seeds and varieties that work for our system. As the roots start to emerge there are ways to enhance the surrounding environment. The roots are the point of absorption of minerals and moisture for plant uptake, so it is vital to help create a good balance in the soil for the roots. One way to enhance root uptake is to add a source of mycorrhizae as this will expand the root mass through the soil and create a network of fungi between the growing roots.

What exactly are mycorrhizal fungi? Mycorrhizae, which means fungus-root, are beneficial fungi that attach to the plant's roots and are fed with sugars and carbons, and in return, bring nutrients and water back to the growing plant. The most common are arbuscular mycorrhizae…. Arbuscular mycorrhizae have hyphae that attach themselves to the root cells and form vesicles.

These create a bond between the plant and the fungi to exchange water and nutrients with the soil. This can have a large impact on plant functions and can certainly affect drought tolerance, plant health and, of course, yield. Some of the reported benefits of adding a mycorrhizal source are less pathogens, better drought tolerance, less transplant stress, enhanced flowering and improved soil structure.

We carry an excellent suspendable powder mycorrhizal inoculum consisting of four species of endomycorrhizal fungi. Read more about MycoApply here. As we are beginning the process of planting for and are enthusiastic about a great season ahead, it is truly very important to plan for success early on and to be mindful to give those seeds the best chance possible to produce a healthy and bountiful crop and yield.

Think about the soil health as you plant your seeds in the ground. Think about the potential of the seed and what it needs for a great germination and what you can do to give it a boost this spring. This can result in slow germination, weakened and diseased seedlings, and even plant death.

It is much better to delay planting until soils warm up. The optimal temperature for growing seedlings may be different from optimal germination temperatures. Table 2 shows the range of day and night temperatures that are best for growing seedlings in a greenhouse, where temperatures can be controlled. Cooler temperatures generally slow down growth, and warmer ones speed up seedling growth. All seedlings need ample light to grow.

If light levels are low or if seedlings are too crowded as they grow, the stems will stretch as the plants seek more light, resulting in weak, "leggy" transplants. Consider supplemental lighting if greenhouse light levels are low. The length of time that seedlings need to grow in the greenhouse before they are big enough to transplant into the field varies by crop.

Tomato and pepper seedlings may take five to seven weeks to produce, while cucumbers and squash are ready to transplant after three to four weeks in the greenhouse. But all transplants need to be hardened off before going from the greenhouse out to the field, or they will be damaged by the harsher conditions. To harden off seedlings, gradually expose them to conditions they will have in the field. Plants may show some signs of wilting, but do not let plants wilt excessively.

After a day or two, weather permitting, set the trays outside of the greenhouse for five to seven days prior to planting. If it is very hot and sunny, provide some shade for the seedlings for the first day or two. Plants that are hardened off in this manner will be better able to tolerate transplanting, and continue to grow in the field uninterrupted. For more information, see " Seed and Seedling Biology ".

Let's Stay Connected. By entering your email, you consent to receive communications from Penn State Extension. View our privacy policy. Thank you for your submission! Home Understanding Seeds and Seedling Biology. Understanding Seeds and Seedling Biology. Photo: Seedling, U. Department of Agriculture, Flickr. Choosing the Right Seed Few decisions are more important to successful vegetable production than choosing the right seed.

The Right Environment to Germinate All fully developed seeds contain an embryo and, in most plant species, a store of food reserves, wrapped in a seed coat. Table 1. Optimal soil temperature conditions for vegetable crop germination.

Managing for Optimal Germination and Seedling Development Testing stored seeds for germination Seeds purchased within a year of when they are to be planted rarely fail to germinate. Uniform germination We know that seeds need proper conditions to germinate rapidly. Seedling development The optimal temperature for growing seedlings may be different from optimal germination temperatures. Table 2. Temperature and time required for growing field transplants.

Vegetable Crop Day o F Night o F Time weeks Broccoli Cabbage Cauliflower Celery Cucumber Eggplant Lettuce Melons Onion Pepper Squash Tomato Seedling maturation and hardening off The length of time that seedlings need to grow in the greenhouse before they are big enough to transplant into the field varies by crop.