Tropical Gardening Helpline: Maximize garden riches by improving soil

  • Swiss Chard is one of the “powerhouse” vegetables recommended by (Photo courtesy /
  • Some vegetables pack more nutritional punch than others. Look online to choose which “powerhouse” vegetables to grow. (Photo courtesy /
  • Choosing vegetable varieties that are rich in vitamins and minerals can help you increase the nutritional value of your garden’s produce. (Photo courtesy /

Kelly asks: I am delighted that I have room on my property to grow some of my own vegetables. I want to be sure I am growing nutritious food for my family. Any suggestions on how to grow highly nutritious vegetables?

Tropical Garden Answer: It’s a good idea to consider getting the best nutrition possible from your garden produce. The nutritional value of many vegetables in the marketplace has been steadily declining over the years. Growing some of your own crops in healthy soil can increase the vitamins and nutrients in what you eat.


The best way to grow nutritious vegetables is to grow them in nutrient rich soil. Before planting, get to know your soil and concentrate on improving its health. Start by doing a soil test.

Standard soil tests will usually give you an analysis of the acid/alkaline rating in your soil and some of its elemental contents. Most vegetables grow best in a soil that is slightly acid with a pH close to 6.5. Ratings above pH 7.3 or below pH 6.2 should be adjusted so the nutrients in the soil to be optimally available to the plants. Find a chart on the effects of pH on soil fertility at

Most standard soil tests include the values of major plant nutrients like phosphorus (P), potassium (K), Calcium (Ca) and magnesium (Mg). Nitrogen (N) is also important to plants but its presence is always changing.

If you have plants in place, you can do tissue samples of the leaves to see which nutrients are actually present in your plants. For a UH publication on soil and tissue sampling go to

You will definitely be on your way to growing more nutritious vegetables if you avoid using chemical fertilizers or any chemical pesticides or herbicides. Using organic supplements and treatments will help you avoid putting heavy metals or other toxic substances into your soil.

Dr. Jana Bogs has been studying the relationship between soil nutrition and the nutrient value of fruit and vegetables grown in that soil for many years. She is a research scientist and consultant whose motto is “Creating health from the soil up!” She will be giving a talk entitled “Growing Nutritious Vegetables” at 10 a.m. Saturday, June 2 at the Kailua-Kona Public Library. This is part of the series of monthly talks presented by the Community Seed Library and sponsored by the Friends of the Library in Kona (F.O.L.K.)

In her presentation, Jana will discuss the value of expanded soil testing to increase your ability to bring your soil to its maximum nutritional value. Her Beyond Organics Growing System relies on a Nutrition GrownTM Soil Test that goes way beyond standard tests. It analyzes many factors and tests for 12 additional nutrients that are important to plant and human health.

Jana will share several ways to increase nutritional values beyond simply applying nutrients. These include selecting the most nutritious varieties, increasing microbial activity and earthworm activity and, in general, giving plants exactly what it is they need to express their full potential.

Her system starts with testing and amending the soil then planting the best known cultivars. As the plants grow, she recommends doing tissue analysis and applying any needed nutrients through foliar spraying. Once plants are mature, she recommends saving seeds from the healthiest and most productive specimens and starting the cycle again.

Beyond the health benefits of growing and eating more nutritious fruit and vegetables, improving soil health will also help your plants. Healthy plants are better able to withstand insect and disease pressure and can also have more drought tolerance. Their produce will likely stay fresher longer and have better flavor as well.

Overall, attention to soil health can significantly improve the nutritional value of the food you grow. Come hear Jana describe her system or learn more about her research and her new book at

Email plant questions to for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column

Diana Duff is a plant adviser, educator and consultant living in a dryland forest north of Kailua-Kona.

Gardening Events

Tuesday: “Coffee Quality Workshop” from 8:30 a.m. to noon at the UH Cooperative Extension office in Kainaliu, across from the Aloha Theatre. International coffee consultant Miguel Meza will discuss ways to create high quality coffee. The workshop will cover growing, picking, processing and storing high quality coffee. Participants are encouraged to bring parchment or green coffee samples for discussion. For more information and to register, go to

Friday: “Master Food Preserver Certificate Program” (first of eight sessions) from noon to 6 p.m. at Hawaii Community College Palamanui campus kitchen, 73-4225 Ane Keohokalole Highway, Kailua-Kona. Additional sessions are on Saturday and Sunday, June 2 and 3 from 9 a.m. to 3 p.m.; Friday, June 8 from noon to 6 p.m.; Saturday and Sunday, June 9 and 10 from 9 a.m. to 3 p.m.; Saturday and Sunday, June 16 and 17 from 9 a.m. to 3 p.m. Tuition is $200. For more information, go to

Saturday: “Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Call Peter at 323-3318 for more information.

Farmer Direct Markets

Wednesday: “Hooulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay

“Sunset Farmers Market” 2-6 p.m. in the HPM parking lot at 74-5511 Luhia Street in Kailua-Kona (across from Target)

Saturday: “Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center

“Kamuela Farmer’s Market” from 7 a.m. to noon at Pukalani Stables

“Waimea Town Market” from 7:30 a.m. to noon at the Parker School in central Waimea

“Waimea Homestead Farmers Market” from 7 a.m. to noon at the Waimea Middle and Elementary School Playground

Sunday: “Pure Kona Green Market” 9 a.m. – 2 p.m. at Amy Greenwell Garden in Captain Cook

“Hamakua Harvest” 9 a.m. to 2 p.m. at Hwy 19 and Mamane Street in Honokaa

Plant Advice Lines



Tuesdays &Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4893

Mondays &Fridays: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or