Humidity can result in poor germination

I bought a packet of Granex short-day seed from a local company, 2 percent germination.

I tried another packet and got five seedlings. I planted bunching onions and leeks at the same time, same soil mix, with good results, and transplanted everything when they were about 6 inches tall.

I somehow killed 4/5 of the bulbed onions. The flavor was sweet, as in sugary, then followed by nose burning pungency. Germination seems to be a problem. I planted Supersweet #9 sweetcorn seeds and got 12 percent germination. I’m thinking my soil might be out of wack. I tested 100 seeds in wet paper towels and got 13 sprouts. — Mahalo, Dave

Poor germination can be a problem, especially in humid climates. Relative humidity influences the moisture content of seed. The higher the moister content, the lower the germination rate will be, especially, after one year.

As a general rule, vegetable and flower seeds can be kept for one year without appreciable decrease in germination. Storage, however, may be extended to 10 or more years under proper conditions; seed moisture and temperature are the most important factors. The drier the seeds, the longer they will store.

In Hawaii, storing vegetable seeds in a dry, sealed glass container should keep most seeds viable for a year. For longer storage, place seeds in a moisture-proof container and store in the refrigerator.

Longevity of vegetable seeds will also vary depending on the species.

For example, collards, cucumber, endive, radish and watercress produce some of the more hardy seeds, rated as lasting five years. Next come beets, cabbage, cauliflower, eggplant, kale, mustard, squash, swiss chard, tomato, turnip and watermelon, rated at four-year longevity; asparagus, beans, carrot, celery, chinese cabbage, New Zealand spinach, pea and spinach, at three years; leek, sweet corn, okra and pepper are rated at two years; and finally, the group which includes onions is rate at a mere one-year longevity — lettuce, parsley, parsnip and onion. Corn isn’t that much better, rated at two.

In summary, germination problems are much more likely to occur with crops such as onions and corn as opposed to such vegetable as cucumber, radish and water cress.

If the seed packs are well within the expiration date, germination should be much greater than 2 percent. Assuming seeds are viable, there are other reasons for poor germination:

1. Planting depth: Onions in particular are small seeds and can easily be planted too deep. They can just as easily be washed away during heavy rains. Consult the seed packet for proper planting depths.

2. Temperature: Some seed need the soil temperature to warm up before they will adequately germinate, while other cool season vegetables like onions, germinate best in a cool soil.

3. Water: Too little and they will not germinate or dry up after germination, and with too much water, they can die from lack of oxygen or be overcome by fungi. Germination failure is most often caused by over watering. Seeds and seedling should always be kept moist but the soil should not be kept soaking wet.

4. Soil pH: Each vegetable seed will have its range in which it will germinate best.

5. Herbicide residues may still be active in the soil causing poor germination. A high fertilizer content in the soil could also hamper germination.

6. Soil insects feed on seeds and/or young seedlings.

7. Finally, different types of soil organisms such as fungi and bacteria can cause seeds to rot, especially under high moisture conditions.

To address the pungency issue: Although sulfur is an essential element required by onions, at high levels in the soil, sulfur can contribute to pungency.

The compound responsible for this is called allyl propyl disulfide. For a more detail explanation of pungency in onions, see

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at Also, visit his website at


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