The Grass Doctor

Fertilizer - Why is it ok to just spread fertilizer rather than put deep in soil close to roots?

I notice that all instructions i have read about putting fertilizer on my lawn (e.g. Scotts Turf Builder Fertilizer and Weed Control) always says to use a spreader (or dropper) to put the fertilizer on the "surface" of the lawn. From my understanding fertilizer contains valuable nutrients for the lawn (its food for the grass) and so i would best think it would work better if the fertilizer was closest to the lawn's roots found far underneath the surfce. So how then is tossing fertiizer on the surface of the grass useful? And wouldn't weeds just use the fertilizer as food too? If it burns them chemically because the fertilizer is so close to them then why do instructions mentions to use fertilizer in a mix with new seedlings -- you dont get closer to that and would that then burn the new seedling because the fertilizer is so close?

Public Comments

1. Because a concentration of all that fertilizer close to the roots will "burn" them chemically.
2. the fertilizer dissolves when it rains and soaks into the ground. That's how it gets to the roots. Yes weeds will also use the fertilizer, that's why you need to spray and kill all of the weeds in your lawn.
3. Because today's topical chemical fertilizers are usually designed on a slow release basis so you don't have to do as much work.They feed your lawn a proper balance with each rain or watering.Who wants to work any harder than we have to?If you are worried about weeds use a weed and feed fertilizer.
4. Systemic is best, not only for the target plant but in general, and needs dillution. Effectiveness is subjective,,, as are brands and claims.
5. Fertilizers are used by homeowners to maintain and improve landscape beauty and quality. Increased use of home lawn and garden fertilizers, however, has caused concern about pollution of lakes and groundwaters. The two fertilizer nutrients primarily involved, nitrogen and phosphorus, are needed by all plants for healthy growth. Although an individual lawn or garden seems small, the total area of lawns and gardens in urban environments can be significant. Runoff and drainage waters carrying these nutrients may move over hard-surfaced streets where there is no soil to act as a filter. The potential result is an increase in pollution problems. Proper fertilizer use can enhance plant growth without polluting the environment. Yet, misuse of fertilizer may not only harm the environment, but may result in injury to landscape plants. In an effort to reduce phosphorus runoff to surface waters, the state legislature passed laws in 2002 and 2004 that restrict phosphorus fertilizer use on lawns. Details of the law are described below. Phosphorus and runoff concerns Phosphorus is one of the macronutrients essential for plant growth. This nutrient can also be a primary cause for lake enrichment leading to growth of algae and weeds (a process called eutrophication). Sometimes phosphorus in lawn and garden fertilizers is implicated as the source of pollution, but this is not always an accurate assessment of the problem. Although misuse or misapplication can pollute lakes, proper application following soil test recommendations does not pose a significant threat of lake pollution and may reduce pollution possibility. The major sources of phosphorus in runoff are from lawn clippings and tree leaves left in the streets and gutters. Other sources of phosphorus may come from soil particles either blown into the lakes by wind erosion or carried in runoff over bare soil. Inorganic phosphorus moves very little in soil. When applied and incorporated as a fertilizer, phosphorus is quickly bound by soil particles. Most of it is not immediately available to plants and doesn’t leach (wash) through the soil into lakes or groundwaters. Although phosphorus is relatively immobile in soils, some runoff containing soil particles and dissolved phosphorus can still occur. Phosphorus taken up by plants is incorporated into organic compounds. If not mixed into the soil, organic phosphorus from plant residues such as lawn clippings and tree leaves is soluble and a potential pollution source. A study of storm runoff into lakes, comparing areas fertilized with phosphorus-containing fertilizer and areas fertilized with phosphorus-free fertilizers, showed little or no difference in phosphorus content of storm runoff.1 However, when street gutters were swept weekly and kept free of plant residue, the phosphorus level was 30 to 40 percent less than in areas where no sweeping occurred. This indicates that plant residues such as lawn clippings and leaves have considerable potential for pollution of lakes whether or not they were growing in fertilized soil. Another source of phosphorus lake pollution is from the settling of phosphorus-containing soil particles moved by wind or water. These sources of pollution are difficult to identify and control. Living plants such as trees, shrubs, and native vegetation around the lake reduce soil erosion and help remove particles from the air and runoff. Some soils are naturally high in phosphorus. Other soils may be high in phosphorus because of buildup from previous fertilization practices. Additions of phosphorus-containing fertilizer to high phosphorus-containing soils are unnecessary. Some soils contain low levels of plant-available phosphorus and additional phosphorus is necessary to maintain healthy plant growth.
6. Unless you plan of turning your lawn under every time you fertilize, how else are you going to get the fertilizer to the roots. The fertilizer companies have done an excellent job in developing a product that can slowly release into the ground after the application. Aeration causes the ground to be less compacted and will aid in the absorption rate. Fertilizer feeds all plants, including the weeds. This is why it important to mow your grass before the weed get to the height to turn into seed and use other methods for weed removal. Fertilizer is just one part of a lawn care plan. The use of fertilizer alone will give you better grass, but better weeds as well. That's why it is important to use fertilizer as a part on a long term lawn care plan.
7. goober_head13 has the best and simplest answer.