Fertilizer Fundamentals: A Lush Lawn and Blooming Garden Start Now

As winter loosens its grip, a thoughtful spring fertilizing plan can mean stronger roots, brighter blooms, and more abundant harvests.

Early spring is a critical time for fertilizing, as plants begin active growth and require nutrients to support root and leaf development. schulzie/Getty Images

Spring is a unique opportunity to take the yard and garden from simply attractive to flourishing, just by providing essential nutrients as plants start growing again after the winter season. Even the southernmost gardens can benefit—while growth might not completely stop in USDA plant hardiness zones 9 and above, it does slow down during the shorter days of winter.

In addition to healthy growth, this feeding can help buff up immunity to pests and disease and add resilience in extreme weather, such as high summer heat. The right fertilizer supports strong root development (the foundation of the yard and garden) and leads to more abundant blooms as well as higher yield/better quality fruits and veggies in the garden.

It can also save money on future feedings and, in the case of lawns, lead to a robust yard carpet that reduces the need for weed control.

Applying fertilizer in spring helps replenish nutrients that may have been depleted during the previous growing season. Adene Sanchez/Getty Images

Proper Timing

Wise old gardeners will advise fertilizing when the soil temperature reaches 50 degrees to 55 degrees F consistently for several days. This is typically mid-April through May for much of the country, but an inexpensive soil thermometer (starting at about $10) will remove the guesswork.

Another clue that signals that the roots are waking up and ready for a good meal—particularly for those in the south, where soil temps remain warm year-round—is new growth: shoots, buds, and blades of grass.

Organic or Synthetic

Organic fertilizer seems the “natural” choice, but it may not always be the best. Organics will build soil health, but the trade-off is they act slowly. Synthetic fertilizers offer fast-acting, visible results, but they can damage the soil over time and must be used only as instructed. They’re generally more affordable.

The trade-off is a contentious issue, ultimately making it a personal decision.

Different fertilizers offer different benefits, making it important for gardeners to choose the option that best suits their soil. mixetto/Getty Images

Grass Types

Grasses are divided into cool-season (fescue, Kentucky bluegrass, ryegrass) and warm-season (Bermuda, St. Augustine, zoysia, centipede). Warm-season types are the exception to the 50- to 55-degree F rule and are fertilized only when soil temps reach 65 degrees F.

It’s important to identify the type of grass you have and its respective fertilization window because fertilizing it too soon will cause top growth at the cost of robust root growth, leaving it more susceptible to disease or drought stress.

At the Store

Healthy lawns will benefit from a balanced fertilizer, while struggling turf may benefit from a high-nitrogen blend. Quality blends are designed for a specific grass type and category and go beyond NPK (nitrogen, phosphorus, and potassium) to include secondary macro- and micronutrients.

If you have a mulching mower, lawn clipping can be left on the lawn for a no-cost organic boost during the mowing season.

Slow or quick release is your next decision. Slow-release formulas offer long-term nutrition and are less prone to lead to excess growth that requires maintenance. Quick-release formulas come in handy when a quick green-up is needed or for soils that are particularly nutrient-deficient.

Granular fertilizer is extremely popular because it can be applied to a large area efficiently with a broadcast spreader, and it comes in slow-release versions. Liquid formulas are simple to apply, offer faster absorption, and don’t require storing a bulky spreader between feedings, as they come in specially designed spray bottles that attach to a hose.

Fabulous Flowers

Perennial flowers are nature’s easy-maintenance joy. Feed them at the first sign of new growth in the spring with a granular slow-release or controlled-release fertilizer (also called “smart-release,” designed to feed for up to six months), then top with compost for additional nutrients and add mulch for water retention.

Choose a bloom-boosting formula with a high phosphorus content, particularly if your soil is phosphorus-deficient. Liquid fertilizer is more budget-friendly but needs to be applied every week or two, or monthly, as directed. The exceptions are azaleas, rhododendrons, and lilacs, which are fertilized right after they have finished blooming. Fertilizing earlier can actually result in fewer flowers. Also, azaleas and rhododendrons need a fertilizer designed for acid-loving plants. You can pinch off spent flowers to encourage more blooms.

Annual flowers use the same fertilizers, starting at the time of transplant.

Granular mineral and organic fertilizers provide roses with essential nutrients for robust, blooming plants. Valeriy_G/Getty Images

Trees and Shrubs

With the exception of fruit-bearing trees and shrubs, most others will not need annual fertilization after the first three to four years. Young ones will benefit from a slow-release 10-20-10 NPK with its higher phosphorus for vigorous root development, or other mixes designed for new trees. Afterward, a slow-release 10-10-10 fertilizer every two to three years should suffice.

Make sure that holly, Colorado blue spruce, mountain ash, dogwood, sumac, and others that thrive in an acidic environment receive an “acid-lovers” blend.

Any concerns? Do a soil test with the local agricultural extension (often less than $15, plus shipping) to confirm that there is adequate NPK and to address any deficiencies.

Fertilizing in early spring, when ground temperatures have warmed enough, allows the plants to use the nutrients most effectively, and promotes strong growth. Options include granular fertilizer, fertilizer spikes, liquid fertilizer, and fertigation (fertilizing through irrigation). Liquid fertilizer and fertigation both will have to be repeated periodically, as instructed, as they are not available in slow-release formulas.

Add some compost for additional nutrients, and top with mulch to retain moisture.

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Fruits and Vegetables

Fruits and vegetables tend to be heavy feeders, consuming and depleting soil nutrients at a rapid rate that should be replenished annually.

Fruit Trees and Shrubs

A granular or spike fertilizer, designed for the particular fruit tree/shrub, should ideally be deployed before the first bud break. It can also be applied as buds begin to swell or at the first sign of new leaf growth. Do a soil test if the trees have yellow leaves or are otherwise suffering.

Garden Soil

Many gardeners simply mix in a slow-release, balanced fertilizer when prepping the vegetable garden bed. Other options include applying a high-phosphorus, slow-release “starter fertilizer” when transplanting. Water it well.

Additional Feedings

While the spring fertilizing may be enough, for a truly abundant harvest, feed with a plant-specific fertilizer as instructed throughout the growing season. This will also improve the quality of the yield. Because fertilizer will keep for several years when stored correctly, consider buying an extra-large bag to save on the per pound cost.