It goes without saying that plants need heat to germinate. Because every spring we can observe anew how warm temperatures bring nature to life. But the seeds of some plants must first go through a longer cold period. It gradually breaks down the existing germ inhibition. Only then can warmth lure a new seedling out of them. This is how you let the cold germs freeze.

Cold germs and frost germs

In the past, all plants that needed a cold period to germinate were referred to as frost germs. However, since the necessary cold period does not always require sub-zero temperatures, this term is not used so often these days. Only the few plant species that actually need frost are still called frost germs. For the other varieties, the more correct term cold germ has become established. The term cooling germ is also occasionally used.

germination inhibition

All seeds contain hormones that promote germination. However, the seeds of the cold germs are simultaneously equipped with germ-inhibiting substances during ripening. This prevents germination immediately after the peel has swollen. Immediate germination is not a problem in consistently warm regions of the world. But in regions where the seasons alternate, timing is important. Because between the seed ripening in autumn and spring, when the new vegetation period starts, there is the cold, growth-inhibiting winter. It must not happen that the fresh seeds sprout in the mild autumn. The young plants would freeze to death in winter without having fully developed.

dismantling of the germ inhibition

At the beginning there is a balance between germ-promoting and germ-inhibiting hormones in the seed of a cold germinator. As long as this remains so, germination is not possible. Therefore, the germ-inhibiting substances must first be broken down. The decomposition process starts as soon as the seeds are exposed to the cold. In the great outdoors, this happens quite naturally due to the low temperatures that prevail outside in winter.
However, it is also possible to artificially bring about the cold that the cold germ needs. Large seed companies have their cold stores for this. In private households, the refrigerator can do a good job in this regard.

period and temperatures

Two questions arise: what temperature is required for the breakdown of germ-inhibiting hormones to begin. And how long does a cold spell have to last for degradation to be completed successfully? These questions must actually be answered separately for each plant variety, because investigations into the facts have brought the following findings:

  • the length of the required cold period depends on the plant
  • on average it lasts four to eight weeks
  • but there are also extremes that take years
  • the optimum temperature also varies from plant to plant
  • a temperature of 0 to 5 °C is sufficient for most seed varieties
Note: The cold period must not be interrupted in between, otherwise germination can be delayed by a whole year.

Known cold germs

In addition to numerous native trees such as oaks, beeches and hazelnuts, many types of flowers also belong to the cold germs. If you sow these cold germs, you should time them so that they get their needed cold spell.

  • cyclamen
  • wild garlic
  • Bergen
  • christmas roses
  • Eisenhut
  • Enzian
  • bluebell
  • Lampionblume
  • lilies
  • poppies
  • peonies
  • cowslips
  • Stockrosen
  • crying heart
  • Waldmeister
  • ornamental onion

sowing time

When sowing the cold germs, we orient ourselves to nature. She lets the seeds trickle to the ground in the fall, where they germinate in the spring. That’s why we humans should also sow cold germs before the great cold sets in.

  • sow in autumn
  • from September to November
  • or in winter
  • December and January

Which of the two seasons is optimal for sowing depends on the plant. Some varieties initially require mild temperatures while the skin swells. Only then can the necessary cold period follow. You should therefore sow these varieties immediately after the seeds have ripened so that they get a few more warm days.

Tip: If you buy the seed, you should pay attention to the information from the seed supplier regarding the time. Corresponding information is printed on the seed packets.

material for sowing

If you want to sow cold germs, you will need the following materials in addition to enough seeds:

  • Sowing tray with drainage holes
  • nutrient-poor seed soil
  • spray bottle for water
  • Maschendraht

A fine-mesh sieve for sifting through the potting soil, a soil stamp and labels can also be useful. However, your purchase only makes sense if you sow often and a lot. A smaller sowing can be done well without these utensils.

Instructions for sowing

  1. Fill a suitable seed tray with potting soil to about 2 cm below the rim. Break up large clods of earth by hand.
  2. Distribute the desired number of seeds evenly over the substrate.
  3. Cover the seeds with a layer of potting soil. This should be as fine-grained as possible. Sift them through a colander or crumble them with your hands beforehand. The finer the seed, the thinner this layer should be.
  4. In order for the seeds to adhere better to the soil, it should be lightly pressed. The easiest way to do this is with a special earth stamp. But it also works with a simple board or similar.
  5. Moisten the soil. Be sure to use a spray bottle for this, as a hard jet of water can sweep the seeds out of position.
  6. Finally, cover the tray with chicken wire to prevent birds from pecking at the seed.
  7. Place the planting bowl outside, where the seeds will get the necessary cold stimulus over the winter. They also tolerate frost and snow. In very rough locations, the place should be protected.
Note: If the seed variety has to stand warm for a few days or weeks after sowing, you should definitely pay attention to this and only put the seed tray outside afterwards.

Cold spell in the fridge

Instead of outdoors, cool germs can also get their cold period in the refrigerator at home. For reasons of space, this is only possible with smaller sowing quantities. Even special seeds can germinate under controlled conditions. Unlike in nature, the cold in the refrigerator is available to us all year round. If necessary, the cold period can take place in the middle of summer.

  • Sow seeds in seed tray
  • Put a plastic bag over it
  • alternatively place seeds in a bag of damp sand
  • Keep seed consistently moist
  • Check regularly for mold
  • Leave in the fridge for as long as the variety requires
  • Warning: do not put in the freezer
Note: Most plant seeds are sufficient for a few weeks in the refrigerator before they are ready for germination. But there are also some varieties that take much longer. For example, the peony can take a full two years to germinate.

After the cold spell

When the sown seeds have survived a long enough cold spell, it is time for new seedlings to grow from them. But this requires heat. How warm and light it can be during germination depends on the variety. Find out in good time about optimal germination conditions so that the effort to break the germs is not in vain. Whether germination takes place indoors or outdoors depends on the season and the temperatures outside.

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