Master Gardener: Exploring why these plants died off in the garden

Q: I tried starting my own seeds inside, but right after they germinated, most of them fell over and died. The base of the stems looked like it was pinched off. What causes this and what can I do to prevent it?

Damping off is a common occurrence, especially with slow-growing seedlings. It is caused by any number of soil fungi and, once it happens, is not reversible. There are some precautions you can take to prevent it (or at least lessen the chances of it happening again). 

Always use seed starter mix when starting seeds. This is a sterile potting soil that is formulated to hold enough moisture to encourage germination but also drains well. It doesn’t have any fertilizers, since these can sometimes encourage fungal growth.

Sterilize your seed trays if they have been previously used. This can be done by spraying them with a dilute bleach solution (1 part bleach to 9 parts water). Let the trays dry thoroughly in direct sun before filling them with seed starter mix.

Read the seed packet carefully and follow the recommended planting depth. Tiny seeds, such as those for lettuce, broccoli, cauliflower, and kale, need to be planted very close to the surface.

Placing a thin layer of sand on top of each cell can minimize moisture on the surface and thus discourage fungal growth. Air circulation is important, so once the seedlings emerge remove any tray covers. Sometimes a fan set at low speed can be directed over the surface of the seed tray to increase air circulation. Applying heat to the bottom of the seed tray will usually speed germination and growth.

While keeping the surface relatively dry is essential, the seed starting mix must not be allowed to dry out. Water from the bottom to encourage strong root development. As soon as you see the first set of true leaves (not the first dicot “leaves”), begin applying dilute liquid fertilizer. The faster the plant grows, the less likely it is to succumb to damping off.

Q: Is gypsum useful in improving soil texture? What exactly is it supposed to do?

Clay soil is a common issue, especially in inland areas. Many newer housing developments are built on super compacted fill and are a real challenge to dig through. This soil is mucky when wet, then dries to a hard, concrete-like substance that cracks excessively. If you try to dig in this soil when it’s not completely dry, it will break up into large heavy clods.

If you’re going to improve this soil, the best strategy is to incorporate as much organic matter as possible. Gypsum (an inorganic substance) is sometimes used to improve soil texture by causing it to temporarily become crumbly. This effect is short-lived since it dissolves and is washed away by rain or irrigation water. Unlike organic matter, gypsum does not improve the overall health of garden soil and is, at best, a temporary fix.

Looking for more gardening tips? Here’s how to contact the Master Gardener program in your area.

Los Angeles County; 626-586-1988;

Orange County; 949-809-9760;

Riverside County; 951-683-6491 ext. 231;

San Bernardino County; 909-387-2182;

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