Scarification, Stratification and Germination
Scarification — why scarify seeds?
In a natural environment, many seeds get battered about with weather (frost, rain, fire), sand, soil particles, and birds and animals’ digestive systems.
It’s called seed abrading or scarification and in the home garden the tougher seeds, which we’ve carefully harvested, may need to be roughened up to mimic nature.
Scarifying allows moisture to enter a seed, which in turn wakes up the dormant embryo and gets it growing. There are several ways…
For manual scarification:
- Use moderate pressure and rub or roll some seeds with coarse sand or grit between your hands for 20 seconds (over paper or tray). Just lightly abrade the seed coat, don’t harm further towards the embryo otherwise the seeds will rot when planted.
- A nail file can be carefully used instead, sandpaper, or even make a nick with the fingernail anywhere on the outer seed coat, preferably opposite the hypocotyls or ‘eye’ which is where the new shoot will emerge from.
Hot water scarification:
- This involves pouring just boiled water into a bowl, let it cool for 30 seconds then tip in the seeds. Leave them in the water to cool, or until they have swelled up to twice their size before planting immediately
Scarification — which vegetable seeds need scarifying?
Luckily most vegetable seeds are soft and don’t need scarifying.
- The exceptions are squash, spinach and legumes (peas, beans) seeds. Even then, it’s not absolutely necessary, but we you find your seed germination rate is poor, experiment with scarification and see if we can improve the odds.
Stratification — why stratify seeds?
Many seeds go into a dormant state and if we want to plant them when we want them to grow, we have to chivvy them along.
We have to give seeds favorable environmental conditions to wake them up ready to spring into life. In nature, dormancy in seeds is usually broken when spring arrives with warm weather and rains, so that’s easy to do, just sow your seeds in warm soil and water them.
However, many seeds prefer to go through the same cycles as nature’s seasons before germinating. So we stratify these seeds. In other words we mimic nature for them, tricky old us — and the seeds respond and burst into life.
It’s a simple matter of chilling these seeds and you can safely do this with most vegetable seeds except for sub-tropical and tropical vegetables, such as melons, peppers, eggplants and similar.
- One method of stratification is to actually sow the seeds in fall or autumn. Let them remain over winter and they will naturally sprout in spring.
- This method has drawbacks in that we may lose seeds if conditions aren’t right… extreme weather patterns, floods, wildly fluctuating temperatures… it’s a bit hit and miss.
- Otherwise, stratify your seeds by mixing with enough moist sand to surround them, seal in bag or container and store in refrigerator for 1-2 months.
- Bring them out and let them dry and slowly come to air temperature, then warm up as the weather naturally warms. Then sow and water these seeds.
The above explanations on Scarifying and Stratifying are very general.
Pre-Sprouting or Chitting Seeds to help them Germinate
Finally, the age old way to jolly along seeds for successfully germinating is to simply pre-soak them.
This takes care of any frustrations may have had if there were gaps of unsprouted seeds in your pots or garden where you KNOW you SOWED seeds.
- Take a tray, layer a few sheets of newspaper or paper towels on the flat bottom, then our in enough water for the paper to absorb it and allow a shallow pool surrounding it.
- Spread out seeds over it, nicely separated so have room to swell and sprout. Keep out of sun, but put in light one you can observe and wait.
- Plant out the seeds carefully as soon as they germinate.
The advantage of chitting or pre-sprouting is that these seeds can usually grow in soil where the temperature would otherwise have delayed germination — especially if you’re having an unseasonably cold snap.
Approximate Times for Vegetable Seeds to Germinate (in normal conditions)
Radish 3-8 days
Cauliflower 4-10 days
Broccoli 5-9 days
Brussels sprouts 5-10 days
Lettuce 6-14 days
Marrow 6-10 days
Melons 6-10 days
Swedes 6-10 days
Sweet Corn 6-10 days
Tomato 6-14 days
Turnips 6-9 days
Chinese cabbage 6-10 days
Cucumber 6-10 days
Pumpkin 6-10 days
Beans (dwarf) 7-13 days
Beans (climbing) 7-13 days
Cabbage 7-10 days
Peas 7-10 days
Silver beet or Swiss chard 7-14 days
Squash 8-12 days
Okra 8-13 days
Beetroot 8-14 days
Eggplant 8-13 days
Broad beans 10-14 days
Capsicum (Peppers) 10-14 days
Endive 10-14 days
Leeks 10-14 days
Onions 10-14 days
Onions (spring) 10-14 days
Spinach 10-18 days
Carrots 10-21 days
Rhubarb 10-21 days
Parsley 10-21 days
Celery 14-21 days
Parsnip 16-25 days
Asparagus 21-30 days
By:- Abhishek Bahuguna
Department of Horticulture
Uttaranchal (P.G.) College of Biomedical Sciences and Hospital