Wednesday | November 22, 2017
About Us | Contact | Subscribe

Is soil safe for potting?

Hi Nick, when I was potting some pineapple crowns, I noticed that the product (Magic Soil - Garden Soil) said not for use in potting. I never noticed this before, and I’ve probably been potting plants with this kind of soil for a long time. Should I be worried? I’ve eaten a pineapple from a mixture of the soil with cinder, so far with no ill effects, but is my head going to fall off or something? — Mahalo, T.

I do not know the specifics for that product, but you can often go to their website to see exactly what it contains. However, I will give you a comment or two about potting mixes. Your worries need not be directed at any toxins in the mix that might be picked up by edibles; rather the worry is about drainage. And with poor drainage, plants will either die or at best, grow poorly.

One difference between a soil amendment to be added to the garden soil, and a potting mix to be put in a container, is drainage. Soil mixes destined for containers are modified to ensure proper drainage and aeration.

They will generally contain ingredients which will ensure good drainage such as sand, vermiculite and/or perlite. Potting mixes need to be well aerated and drained while retaining enough moisture for plant growth.

When choosing potting media, never use garden soil by itself no matter how good it looks or how well things grow out in the garden. When garden soil is put into a container, both drainage and aeration is severely impeded.

We recently moved to Pahoa (Hawaiian Shores) and have planted corn in the garden. The corn is tasseling and showing silk on stalks that are averaging about 3 feet tall. Any idea as to what is happening? All the corn I have grown previously in Southern California grew stalks over 6 feet. We have fertilized the plants with nitrogen and 14-14-14. The corn is Silver Queen Hybrid which has been in the ground for about two months. I have also planted UH No. 9 about a month ago to see if it will do better. —LQ

Corn plants in Hawaii should also grow to about 6 feet. The rate of growth for corn plants, as with many others, will depend upon temperature. So if the weather is cooler than normal, a slowing will occur. I do not think, however, it was cool enough to warrant 3-foot corn. All kinds of insects, diseases and nematodes can cause stunting in corn. My best guess is that the plants are not getting enough nitrogen. Up to a point, the more nitrogen applied the higher the yield, which is a reflection of plant growth. Coming from California, you are probably not used to the large amount of nitrogen that leeches from Hawaiian soils; this is due to the high volume of rainfall and porous soils. California soils can be very forgiving if nitrogen is not applied often, not so in the rainy areas of the Islands.

Recommendations are to apply about 2 1/3 pounds of triple 16 before planting. Then, additional nitrogen should be provided when the plants are about 6 weeks old; apply approximately one pound of ammonium sulfate or one-half pound of urea per 100 square feet. The nitrogen is important because of leeching and because corn utilizes 2/3 of its nitrogen requirement after six to eight weeks of growth.

There is a dwarfing virus called maize mosaic virus which is transmitted by leafhoppers. It can stunt and even kill plants. All Hawaiian sweet corn varieties, however, are resistant to this virus.

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


Rules for posting comments