Ask the Plant Doctor! Cultivating vegetables from seeds

Beet seeds being planted into fertile soil. If you have been reusing the same medium without replacing it, it may have become overly wet or contaminated. Photo: 123rf

Do you have a question about plants or how to maintain your garden? Send your questions to the Plant Doctor! Email your questions to [e-mail] with "Plant Doctor" in the subject field. Questions may be edited for brevity and clarity.

Q: I have tried growing vegetables from seeds quite successfully two to three times but lately, when I sowed the seeds, they did not seem to sprout, except for bok choy and caixin. Vegetables such as kale and lettuce, and other seeds do not seem to sprout, as mentioned above. What is the cause of, and how to ensure, a higher germination rate? Can this be due to contamination of the sowing medium, wrong sowing medium, contamination in germinated pods, etc? I need to know the root cause to avoid wasting time and material. Look forward to your reply and thanks in advance. – KL

Bok choy (Brassica rapa var. chinensis) and caixin (Brassica rapa var. parachinensis) seeds are hardier than lettuce seeds because of their greater tolerance to temperature fluctuations and various soil conditions. Although generally easy to germinate, lettuce seeds require more specific conditions and are more sensitive to temperature and moisture variations. This makes bok choy and caixin more adaptable and easier to grow, particularly in less controlled environments.

However, the sowing medium might be contributing to your germination problems. If you have been reusing the same medium without replacing it, it may have become overly wet or contaminated. To reduce the risk of diseases and waterlogging, a clean or sterile seed-starting mix should be used instead of garden soil.

Another factor is seed viability, which refers to the ability of the seeds to germinate. During storage, seeds are not entirely inactive; they use a small amount of energy for maintenance (survival) respiration. When seeds absorb water, germination begins, triggering a rapid increase in seed respiration. The seed’s energy must be sufficient to support the seedling from germination until it develops its first set of functioning leaves and can produce its own food through photosynthesis.

Seed viability depends on the initial energy stored in the seeds, the energy used during storage, and the remaining energy available for germination until photosynthesis begins.

As storage time increases, seed viability decreases due to the gradual depletion of the remaining energy.

Storage temperature, air humidity and seed moisture are three essential factors affecting seed viability. Storing seeds in a cool, dry environment helps to reduce seed respiration and increase viability, whereas a warm, humid or wet environment can increase the respiration rate. Seed viability is halved for every 1% increase in seed moisture content or every 5°C increase in storage temperature.

The optimal air temperature for maintaining seed viability is below 15°C, with a relative humidity of 20-40%. Because Malaysia typically experiences daily air temperatures and relative humidity above these ranges, seeds should not be stored in the open.

Instead, they should be placed in airtight packages and stored in a cool, dry place. If the seeds are not stored properly or are too old, they may no longer be viable after repeated use.

Assoc Prof Dr Christopher Teh heads the Department of Land Management, Faculty of Agriculture, Universiti Putra Malaysia. His field of specialty is in soil and water conservation. The views expressed are entirely his own.