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GROWING TOGETHER: How to fertilize trees, shrubs, flowers and fruits

Granular fertilizer should be cultivated in shallowly and then watered. Michael Vosburg / Forum News Service

Have you ever struggled with a some-assembly-required item, and hours later concluded that whoever wrote the instructions obviously never actually put one together?

That's the way I felt the other day when I simply wanted to add fertilizer around our arborvitae.

I even decided to read the directions. The bag of 10-10-10 was headlined for trees, shrubs and flowers and said to apply 1 pound per 100 feet of row. But I don't have 100 feet of arborvitae. Just tell me how big of a scoop to sprinkle around each, as in how many cups.

Lawn fertilizing is comparatively easy, as you measure the lawn area and apply at the rate on the label. But fertilizing trees, shrubs, vines, fruits, perennials and annuals is often less clear-cut. Let's examine the guidelines for non-lawn plants.

• Plants need nutrition like humans need food, and the three elements required in greatest quantity are nitrogen, phosphorus and potassium, which are the three primary numbers listed on every fertilizer label.

• Lawn fertilizers are high in nitrogen, the first number in an analysis like 30-5-5, to promote green, leafy growth.

• Trees, shrubs, perennial flowers, annual flowers, fruits and vegetables require a more "well-balanced" or "complete" fertilizer, in which the three main nutrients are closer in proportion, such as 10-10-10, which provides nitrogen for green, healthy foliage and phosphorus and potassium for flowering, fruiting and root development.

• Although many fertilizers are specially packaged for plants like roses, tomatoes or trees, an all-purpose, well-balanced fertilizer like 10-10-10 is effective, eliminating the need for many individual types.

• Dry granular fertilizers or water-soluble Miracle-Gro types are both beneficial.

• Soils in the Upper Midwest are generally considered fertile. Adding fertilizer can boost growth and production, helping plants reach their maximum.

• Fertilizer isn't medicine for sick plants. Force-feeding a declining plant can make matters worse. Fertilizer turns an OK plant into a more prolific plant.

• For best results, soil testing of gardens and yards can provide a baseline to determine present fertility and recommend additions. North Dakota State University and the University of Minnesota both have soil-testing labs.

• Don't fertilize during dry periods. Plants can't use fertilizer without adequate moisture. Fertilize before a rain, or water after application.

• Organic fertilizers are derived from plant or animal sources. Manure, compost and other organics are usually lower in fertilizer analysis with nutrients released slower but are longer-lasting, plus they enrich soil tilth.

• Inorganic or chemical fertilizers are derived from minerals or manufactured products. They react faster than most organics and are higher in analysis, but dissipate quicker and they generally don't improve soil tilth.

• Both organic material and inorganic fertilizer can be combined effectively, if desired.

• Apply fertilizer to trees, shrubs, fruits and perennials when spring's flush of rapid growth begins, and then monthly through June.

• July 4 is the cutoff date for fertilizing trees, shrubs, fruits and perennial flowers. Fertilizing later stimulates growth that might not have sufficient time to toughen or harden off before winter.

• Fertilizer is especially effective on younger trees, shrubs, fruits and perennials. Older, large, established plants usually grow fine without fertilizer additions.

• Starter fertilizers help vegetable and flower transplants establish quicker.

• If in doubt about quantity, always err on the low side, as too much can burn plants. Follow the label.

• Granular fertilizer is best cultivated shallowly into the soil surface after application and watered in.

• Fertilizer spikes provide nutrition, but materials don't move laterally a great distance, limiting spikes' efficiency.

• For vegetable gardens, fertilizer can be broadcast and tilled in before planting, or side-dressed in bands beside rows or in a circle around individuals. Follow label directions, which for 10-10-10 is about 2 cups (1 pound) per 100 square feet or about a half cup per 10 running feet of row.

• For trees, apply 1 cup of 10-10-10 for every inch of trunk diameter (measured 4½ feet above ground level) and distribute evenly around the root zone inside and outside of the canopy's dripline, not next to the trunk.

• For shrubs, spread 1 cup of 10-10-10 evenly around large, 5- to 6-foot-high established shrubs. Apply a half cup to small and less-established shrubs.

• For perennial flowers, rhubarb and asparagus, spread 1 cup of 10-10-10 per 100 square feet of bed, or band each plant with a fourth to a half cup. Cultivate in and water.

• For strawberry patches, follow vegetable garden guidelines.