As a substitute for in-person programming, we’re offering a series of posts on starting a vegetable garden. This science-based information comes from the Seed to Supper program, developed by the Oregon Food Bank. During these difficult times, the Oregon Food Bank welcomes your donations.
OSU is also offering its vegetable gardening class online.
For a healthy garden, you’ll need healthy soil. Many problems in the home garden have nothing to do with disease or insects but are caused by poor soil. If you have dry, cracked soil, soil that’s hard to dig, or soil that doesn’t absorb water (or drains too quickly), you may have poor soil.
Soil that’s “in good tilth” can support plant life. It’s loamy, easy to dig, readily soaks up and stores water, drains well, and makes a good seedbed. Loamy soil will form into a ball and hold its shape when moist, but it will easily crumble when you squeeze it.
Clay soil holds more moisture and has less air than sandy soil. It can be harder to work, and it warms slowly. Sandy soil drains better than clay soil, has more air, and warms quickly, but it loses moisture faster.
Garden soil is made up of air, water, organic matter, and tiny pieces of broken rock. It’s roughly ½ pore space, or empty space between soil particles. Water fills the small pores, and air fills the large pores. If the broken rock is mostly sand, the soil pores hold a lot of air and not much water. If the broken rock is mostly clay, the soil pores hold a lot of water and not much air. Plants and their roots need both air and water to grow.
Organic matter makes up only a small part of healthy soil, but it’s essential in a vegetable garden. Organic matter is anything that was once living and is now decomposed—or broken down—in the soil. Adding organic material improves both clay and sandy soil.
In nature, soil microorganisms and earthworms decompose raw organic materials like fallen leaves, plant trimmings, and food scraps until they cannot be broken down further. You can then add this decomposed material to your garden beds as compost, which we’ll discuss in more detail in our next post. Planting in raw organic material can harm your plants, so it must decompose before you use it in your garden.
Consider testing your soil when you are starting a new garden. A soil test can measure your soil’s pH and the amounts of N, P, K and other nutrients in your soil. Testing the pH tells you how acid or alkaline your soil is. Vegetable gardens are most productive when the soil is slightly acidic between 6.0–7.0. If your soil pH is lower than 6.0 (too acidic), then some nutrients will be less available to your plants. You can raise pH by adding agricultural lime, which also adds calcium to the soil. Apply 5 pounds per 100 square feet of growing area (or more, if pH is especially low).
N-P-K stands for essential nutrients nitrogen, phosphorus, and potassium. If you’ve applied a balanced fertilizer for several years, your soil may already have enough phosphorus and potassium. Nitrogen can leach out of the soil quickly with too much watering or heavy rainfall. You may want to test your soil every three to five years to see if you really need to supply any nutrient other than nitrogen. You can purchase inexpensive test kits for pH and N-P-K at local garden centers (call ahead to check availability) or online.
Vegetables grown in containers will need more fertilizer than those grown in the ground. The soil (potting soil only!) must be refreshed or replaced annually.
Next up: Compost and Fertilizer