Cold and frost germs need weeks of cold stimulus for germination. We present the phenomenon and some representatives of cold germs and give tips for sowing.
Not all seeds are immediately germinable after harvesting and drying in autumn. Many of our native plants are cold germinators or cool germinators. We will introduce you to the phenomenon, explain what this means for the seeds, provide a list of cold and frost germs and give tips on how to get them to germinate after all.
Cold germ: what does it mean?
Frost or cold germinators are plants whose seeds cannot germinate or can hardly germinate without a longer period of cold. The seed is in a seed dormancy, the so-called dormancy. This dormancy can be caused by a very hard seed coat, a plant embryo that is not yet fully developed inside, or by germ-inhibiting substances in the embryo or nutritive tissue. Unfavorable environmental conditions such as drought also prevent the seeds from germinating. Many seeds are a combination of different dormancy types that must be overcome before germination can occur.
The cold germs are mainly germ-inhibiting substances inside, which trigger dormancy. A highly concentrated plant hormone, abscisic acid, is mostly responsible for this seed dormancy. This hormone is intended to prevent cold-sensitive plants from germinating in autumn and dying and freezing to death in the following winter frosts. Instead, these seeds will survive the winter outdoors, only germinating in the spring when temperatures rise again. Due to the week-long cold stimulus, the abscisic acid is slowly broken down and the seeds can finally sprout. The effect of cold either occurs naturally outdoors or it can be simulated artificially in the refrigerator or freezer.
The process of breaking up dormancy through artificial cold is also called stratification. In addition to most native tree species, cold germs also include numerous ornamental and useful plants in our gardens. yourSeeds are designed to wait out the cold winter first and not germinate until the following spring. In mild or tropical warm areas, the seeds of the native species usually germinate directly, since they do not have to fear any frost or winter and a cold-dependent dormancy would make no sense.
Note: The term “cold germ” includes frost germs and cold germs. The former need significantly colder temperatures to break through the seed dormancy than the chilled germinators, which are adapted to milder winters.
List of cold germinators
Cold germs are generally at home in the temperate and polar zones, which also includes many of our native plants. The following list gives you an overview of cold-germinating useful and ornamental plants.
Which vegetable is a cold germinator?
For vegetables, there are very few cold germs, because many species that we tend and care for in the garden come from significantly warmer areas where the seeds do not need any dormancy. These include the almost forgotten chervil (Chaerophyllum bulbosum) as well as the two perennial vegetables wild garlic (Allium ursinum) and sea kale ( Crambe maritima), which only requires mild temperatures above 5 °C. Lettuce (Lactuca sativa) does not germinate cold, it is only preferred to be grown in the cooler months of spring and autumn, as it tends to bolt in summer and then no longer tastes particularly good.
Which types of fruit are cold germinators?
Many types of fruit that grow here let their seeds rest in winter. These include hazelnuts (Corylus avellana), walnuts (Juglans regia), wild fruit such as cornel (Cornus mas ) and all rose plants (Rosaceae). This large family includes apples (Malus x domestica) and pears (Pyrus communis), as well as stone fruit - Cherries (Prunus avium), plums (Prunus domestica subsp. syriaca), plums (Prunus domestica ) and Co.
Which herbs are cold germinators?
Many herbs that occur naturally in our latitudes also germinate cold, for example chives (Allium schoenoprasum), dill (Anethum graveolens) and sage (Salvia officinalis), Woodruff (Galium odoratum) and Arnica (Arnica montana).
Which flowers are cold germinators?
Also some native annualsFlowers that reproduce by seed are among the species with a cold-dependent seed dormancy. Typical cold germs are poppy (Papaver), cornflowers (Centaurea cyanus), some campion species (Silene ) and violets (Viola). Also snapdragons (Antirrhinum), some mulleins (Verbascum), the pretty corn radish (Agrostemma githago), the annual Silverleaf (Lunaria annua) as well as some Heron's Bills (Erodium) and some Spurges (Euphorbia). to the cold germs.
Which perennials are cold germinators?
Many of our native perennials are cold germs because their development has adapted to the cold winters in our latitudes. Exotic perennials from warmer areas, on the other hand, often do not have dormancy. Cold-germinating perennials include, for example, adonis (Adonis), Christmas roses (Helleborus niger), phlox (Phlox ), peonies (Paeonia), cowslips (Primula veris), forget-me-nots (Myosotis) and also the Lavender (Lavandula angustifolia) is a cold germinator.
List of cold germs at a glance:
- Vegetables: Chervil turnip, wild garlic, sea kale
- Fruit: hazelnuts, walnuts, cornel, rose family, stone fruit
- Herbs: chives, dill, sage, woodruff, arnica
- Flowers: poppies, cornflowers, some types of campion, violet, snapdragon, mullein, corn radish, silver leaf, some egrets, some spurge plants
- Perennials: Adonis, Christmas rose, Phlox, peony, cowslip, forget-me-not, lavender
Sowing cold germs: How to do it
There are two ways to successfully germinate cold germinating seeds. With little effort, you can simply sow the frost germs outside in late autumn from October to November in the bed or in a seed container that you leave outside over the winter. When sowing the cold germs, pay attention to the respective planting depth of the seeds and mark the spot with a label so that you also know later what will grow here in the spring. Now you can leave the seeds alone over the winter, because they are still dormant anyway and do not require any additional care. From March, the seeds begin to germinate with rising soil temperatures. jeDepending on the species, it can take until mid-April before you see the first seedlings. Outdoors, cold germs can also be sown in summer. However, they do not germinate until the following spring.
Tip: Some seed dealers of heavily dormant seeds sell seeds with already broken dormancy. They are only in a waiting state before germination, which is achieved through drying. They have a limited shelf life, but germinate as soon as they are sown. The procedures for achieving this state are usually patented and have special suffixes.
How to sow cold seedlings outdoors?
- Sow in late autumn from October to November in a border or in a seed container outside.
- It is best to mark the sowing spot so that you can still find it in spring.
- Germination begins between March and mid-April as temperatures rise.
- Some seed shops sell broken dormant seeds that no longer need a cold stimulus.
A non-seasonal method is to break seed dormancy using the refrigerator. Cold germs can be stored here for a few weeks all year round and then germinated. It is important to let the seeds soak in warm water for one to two weeks. Dry seeds will hardly germinate even after cold treatment. Now mix the seeds with potting soil, about one third of which has been improved with sand.
Our Plantura organic herb and seed soil is ideal for this because it is low in nutrients and at the same time has a very loose consistency, which facilitates germination. Wet the seed-soil mixture well and place in a freezer bag. Write the date on it so you can keep track of the weeks the bag will be in the fridge.
Alternatively, you can also put whole seed trays in the fridge. Here, however, it is important to ensure that the substrate never dries out. A cling film can easily remedy this. Depending on the plant species, the duration and optimum temperature for the end of dormancy vary. In general, seeds from cold germs require temperatures between -4 and 4 °C and three to twelve weeks of stratification. However, some trees even need a few months of cold weather. After sufficient time in the refrigerator, place the seed trays on a mild 5light up to 12 °C. Simply layer the soil mixture from the freezer bag flat in a seed tray. With the slightly higher temperatures, the seeds are now beginning to germinate. After a few weeks, pricking and implementation can take place as usual.
How do you sow cold germs in the fridge?
- The seed dormancy can also be broken in the refrigerator.
- For this purpose, the seeds are stored in the refrigerator for a few weeks in a freezer bag filled with potting soil and sand in a ratio of 2:1.
- Alternatively, whole seed trays can be placed in the refrigerator, but the substrate must not dry out.
- Depending on the plant species, different temperatures and lengths of the cold period are required for germination.
- If enough time has passed, the seeds are sown in seed trays or the finished seed trays are placed in a suitable location.
- A bright place at 5 - 12 °C is ideal for germination.
Whether cold germinator or not, first we have to get seeds from all plants and dry them well and store them until the next sowing. We give tips on each species and how to get good seeds from them.