Fertilizing plants now is an investment in the future
"Growing Together" columnist Don Kinzler says proper nutrition is the basis for nearly all plant growth, so it's worth getting right.
FARGO — A young homeowner was lamenting to the experienced gardener next door that her rhubarb wasn’t producing large, tasty stalks. “Have you tried manure on your rhubarb?” asked the old gardener. “No,” she replied. “We prefer sugar.”
Rhubarb isn’t the only plant that produces better with additional fertilizer. Proper nutrition is the basis for nearly all plant growth.
The following are tips for fertilizing the plants in yards, landscapes, gardens and flower beds.
- Plants need nutrition just as humans do, and the three elements required in greatest quantity by plants are nitrogen, phosphorous and potassium, which are the three primary numbers listed on every fertilizer label.
- For best results, soil testing of gardens and yards can provide a baseline to determine present level of fertility and recommend any additions needed. North Dakota State University and University of Minnesota both have soil testing labs. An online search of their labs will give information on how to collect samples and where to send.
- Lawns require fertilizers relatively high in nitrogen, which is the first number in an analysis like 30-5-5, to promote green, leafy growth. Fertilize lawns around Memorial Day and Labor Day.
- Trees, shrubs, perennial flowers, annual flowers, fruits and vegetables require a more well-balanced or “complete” fertilizer, such as the common 10-10-10, which provides nitrogen for green, healthy foliage and phosphorous and potassium for flowering, fruiting and root development.
- Fertilizer formulations include dry granular types and water-soluble types you mix with water. Both can produce good results.
- Although many fertilizers are specially packaged for plants like roses, tomatoes or trees, an all-purpose fertilizer like granular 10-10-10 or the common national brand of water-soluble fertilizer 24-8-16 can be effective for all, eliminating the need for many individual types.
- Since plant roots don’t have teeth to chew granules, granulated fertilizer must dissolve into a liquid so roots can absorb the solution. Granular fertilizers are best incorporated into the soil and watered to activate.
- 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 most enrich soil tilth.
- Inorganic, or synthetic, fertilizers are derived from minerals, or manufactured products. They react faster than most organics and are usually 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.
- Vegetable gardens benefit from fertilizing in June to increase quantity and quality of produce.
- Annual flowers in containers or flower beds can be fertilized throughout the growing season to promote continued bloom.
- Geraniums are considered heavy feeders, and respond well to water-soluble fertilizer applied every two weeks for prolific bloom.
- June is a good month to fertilize perennial flowers, fruit, shrubs and young trees, with July 4 being the cutoff date. Fertilizing after July 4 stimulates growth that might not have sufficient time to toughen or “harden off” before winter, leading to dieback.
- Fertilizing perennial flowers in June promotes healthy growth and bloom both this year and next. Next year’s performance often depends on the nutrition perennials receive this year.
- Young trees can benefit from fertilizer, but older, established trees generally grow fine on their own.
- Fertilizers in spike form provide nutrition, but materials don’t move laterally a great distance, making spikes less effective than granular or water-soluble types.
- For vegetable gardens, fertilizer can be broadcast and tilled in before planting, or side-dressed in bands beside rows or in a circle around individual plants. 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 young trees, apply 1 cup of 10-10-10 for every inch of trunk diameter, measured 4.5 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 established shrubs. Apply a half cup to small, young 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 strawberries, apply about a half cup of 10-10-10 per 10 feet of row.
Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at email@example.com.