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Using Fertilizer and Mulch in Your Garden

A lot of plants will survive in a yard without any additional fertilizing. However, if you want your landscape to look its best, there are some plant species and types of conditions where added fertilization would be recommended.

Plants draw nutrients, mainly minerals, from the soil to grow and be healthy. This makes sense since naturally soils have a lot of rock and other mineral based elements in them. They can, however, lose the proper level of nutrients for certain plants under specific conditions; farmers constantly face this issue after crops have depleted the soils.

Applying mulch to the topsoil of planter beds will allow it to degrade and provide organic nutrients as it ages, mulch, therefore needs to be reapplied as it thins or reduces.

A few notes about fertilizer:

  • Fertilizer is not plant food. Plants make their own food through photosynthesis. Fertilizer provides supplemental elements that are often lacking in the soil, such as nitrogen and potassium, think of them as vitamins.

  • Not all plants require fertilizer. If the soil in which a plant lives is rich in nutrients and the microbial life that aids in the plant’s uptake of these nutrients, then adding more can disturb that healthy ecosystem.

  • More is not better. Plants use only the nutrients they need, to absorb more than are necessary can result in abnormal growth.

  • Slow is the way to go. Slow release granular fertilizers give out nutrients in a controlled, “digestible,” and safe manner, as opposed to fast-acting, synthetic, water-soluble fertilizers, which are in essence, an overdose.

  • The extra costs pay off. Synthetic, water-soluble fertilizers are less expensive than slow-release products, but slow-release fertilizers don’t need to be applied nearly as often. Plus, they don’t leach into and pollute waterways, as do many of the synthetic, water-soluble fertilizers, which plants can’t fully absorb.

  • Most garden fertilizers contain the three primary plant nutrients: Nitrogen (N), phosphorous (P) and potassium (K), plus small amounts of other minor nutrients. The NPK ration on the package tells you the percentage- by weight- of each major nutrient. Nitrogen is essential for fueling new growth, most soils are low in nitrogen because it’s a water-soluble nutrient that gets washed away by rain or gets used by plants and microbes. Phosphorus stimulates root growth and helps plants transfer energy between their roots, leaves and flowers. Potassium helps plants move water, nutrients and carbohydrates from one area to another, it’s also responsible for stimulating early growth, improving hardiness and increasing resistance to insects, pests and diseases.

When and How to Fertilize

Woody plants and perennials absorb nutrients from the soil during the growing season, they require few nutrients while dormant. Therefore, apply fertilizer as soon as the plants begin to break dormancy in the spring. Follow instructions on the label as to how often you need to apply, which will depend on the type of fertilizer used.

Note: stop applications after the first fall frost.

Food crops also benefit from an early start fertilizing schedule. Some “feed” on fertilizers lightly, while others are considered heavy feeders- they require more regular applications throughout the growing season.

In general, applying granular fertilizers just before a good rain can be beneficial, as it aids in working the fertilizer down into the soil where roots can access it. In the case of liquid foliar sprays, its best to apply them on dry days in either the early morning or the early evening when the leaves will have time to absorb the material; avoid extremely hot days when foliage is subject to burning.

Not all plants need the same amount of nutrients or need them at the same time during the season. Always follow packaging directions because application rates vary depending on the nutrient content, whether its synthetic or organic and whether its granular, timed-released or water-soluble.

New Trees and Shrubs: When planting new trees and shrubs, incorporate fertilizer into the root zone to ensure the plants have access to a slow and steady supply of nutrients. Established trees and shrubs may be fertilized once a year in early spring. If the soil is fertile and the plantings are healthy and well established, there may be no need for fertilizer.

New Perennials: When planting new perennials, mix an organic, all-purpose fertilizer into the planting hole to make sure the plants have access to the phosphorus, potassium and other nutrients they will need. Established perennial gardens, berries and perennial food crops such as asparagus and rhubarb can be fertilized once a year in early spring.

New Annuals: Most annual flowers and vegetables are hungry plants. Use a granular all-purpose fertilizer at planting time and then apply a liquid fertilizer once or twice a month through midsummer.

More Isn’t Necessarily Better

Though you don’t want to let plants go hungry, applying too much fertilizer can cause problems. Plants that get too much nitrogen will produce lots of foliage but few flowers and fruit. Too much phosphorus in the soil makes it difficult for plants to absorb iron and zinc; too much potassium prevents them from absorbing calcium. Excess fertilizer can also wind up in groundwater and waterways, damaging ecosystems and polluting drinking water.

Always follow package instructions for application rates and timing, if in doubt, be conservative.

Plant PH

Plants absorb nutrients through their roots, so the nutrients need to be dissolved in water. Some nutrients won’t dissolve if the soil is very acidic (pH 4-5) or very alkaline (pH 8-9). This means even if they’re present in the soil, they won’t be available to plants. When the pH is between 6 and 7.5, most soil nutrients dissolve relatively easy, which is why most plants prefer this “neutral” range. That said, some plants prefer a high or a low pH. Blueberries, for example, grow best in acidic soil with a pH between 4 and 5.

Soil is largely composed of weathered rock fragments and its these rocks that determine the soils natural pH level. Soil pH is also affected by rainfall, temperature and vegetation. Some parts of the country have characteristically high or low pH levels. The only way to know for sure is to test the pH of the soil. There are a lot of kits you can buy for this.

Based on the test results, you can adjust the pH of the soil if needed. Changing the pH level may require you to add something like lime (to raise the pH) or elemental sulfur (to lower the pH). Always take a conservative approach to adjusting pH levels. Changes happen slowly and it’s easy to go too far in the other direction.

Adding organic matter to the soil, such as compost, shredded leaves or leaf mold, has a “buffering” effect on pH and can help keep levels relatively consistent.

Aerating Soils and Lawns

As mentioned earlier, plant life needs air to survive, just like we do. Solis that become too compacted don’t allow air into them. Therefore, you should aerate your lawn and garden beds.

To aerate a lawn, professionals will take out little plugs or use spokes to drive holes in the lawn; you can find stuff online that will help you do this.

To aerate soil, you can use a thin shovel, spiked garden wheel, hand trowel or small tiller to work the soils. The goal is to loosen the uppermost 6 inches of soil or more to provide plant roots with plenty of growing room. Consider mixing amendments or slow release fertilizers into your soil when aerating.

How often you aerate depends upon your soils condition, soil can go from sandy to clay. Sandy soil has larger particles in it allowing for air and moisture to move through more easily. Clay soils are made up of very fine particles making it harder for water and air to move through.

A good rule of thumb is to aerate your lawn and soil beds once a year. If the soils are sandier, you can go two years, but if they are clay you may have to aerate more than once in a year.

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