Question
I am confused. As many ?'s as Ive looked up I still am not sure what to use on my newly started lawn, The sprouts are not even an 1" yet. Scott's starter which is expensive is a 20-27-5 formula, Local stores say I can use a 10-10-10 or a 5-10-10 that its not much different. I dont want to damage these tender sprouts so what should i do?   Thanks for your time Tammy

Answer
Fertilizer has 3 numbers shown such as 20-27-5, 10-10-10, 5-10-10, etc.

These numbers represent the PERCENTAGE of ACTIVE INGREDIENTS of the 3 main nutrients which plants needs. These 3 ingredients are: nitrogen (N), phosphorous (P), and Potassium (K). They are always listed as N-P-K. E.g. a 29-3-4 fertilizer contains 29% nitrogen, 3% phosphorous and 4% potassium.

Each ingredient is responsible for various functions in plants, but generally (very generally) you can say that:
N - Nitrogen is responsible for green growth
P - Phosphorous is responsible for fruiting, flowering, root development
K - Potassium is responsible for cell structure, disease and draught resistance and ability for the plants to take up other nutrients.

Therefore, all plants require N, P, and K, but depending on the type of plants, some require more N compared to P, K while others require more P,K and less N for example.

For example:
- flowering plants need nitrogen to grow plant steams and leaves, but they consume large amounts of phosphorous and potassium to develop flower buds, seeds, etc. Too much nitrogen can also reduce flowering ability and therefore a 10-10-10, 5-10-10 etc is generally recommended for flowers.
- fruits are similar. Nitrogen is needed for plant, leaves and stems, but fruiting takes lots of phosphorous and potassium. A 5-10-10, 10-10-10 is recommended.
- In early spring, fruits and flowers will develop lots of green material (the plant grow to a certain pre-set size) and therefore the need for nitrogen is faster in spring vs summer (where the flowering would occur). Therefore many gardeners will fertilize flowering plants with a 20-10-10 fertilizer in spring followed by a 5-10-10 or 10-10-10 in summer.

- grass will not grow flowers and fruits, and the majority bulk production are green leaves which require lots and lots of nitrogen (N). This is why lawn fertilizers typically have much higher N compared to P and K.

A 29-3-4 fertilizer, for example will provide enough P and K (2nd and 3rd numbers) to provide basic plant structures, roots, etc while the N is much higher because as you mow the lawn, more and more green leaf tissue is removed which needs to be replentished (regrown) and that takes primarily N. A lawn therefore consume much more N than P, and K. A flower, as mentioned above, will contain more P and K compared to N.

Therefore (and yes I AM getting to the point) if you have to apply lawn fertilizer to your lawn, I would rather recommend one with high N levels, such as 28-0-0 or 46-0-0 (Urea) over a 5-10-10. A 5-10-10 or 10-10-10 is fine as a single application in early spring (or right after seeding) to ensure that the soil has sufficient quantities of P (phosphorous) and K (potassium) and providing some nitrogen (which wont be consumed in large quantities when seedlings are only 1" tall).

However, shortly after, the grass will start to consume much more N. At this time, I recommend switching to a high N fertilizer. Scott's turfbuilder (or Miracle grow lawn fertilizer) has 29-3-4 and are reasonable priced. However, you might as well use 46-0-0 urea (can be purchased in bulk at farm supply stores and is dirt cheap .. no pun intended).

The only thing to remember is that each application of nitrogen should not be too concentrated or you risk burning grass plants.

To determine how much to apply, you would divide the number "100" by the number of N in the bag. E.g. you would use 100/46 = 2 lbs (roughly) per 1000 sq feet of Urea (46-0-0). If you bought a 20-27-5, you would apply 100/20 = 5 lbs per 1000 sq feet. If you bought a 5-10-10 you would apply 100/5 = 20 lbs per 1000 sq feet. This is because the 46-0-0 is more than 9 times as concentrated (in nitrogen) compared to a 5-10-10. A 46-0-0 fertilizer contains 46% nitrogen per pound. A 5-10-10 contains only 5% nitrogen / lb.

If you fertilize larger areas, then use roughly the number "4,350" divided by the first number on the bag (N) to get the amount of pounds per acre. E.g. you would need roughly 100 lbs of Urea (46-0-0) for one acre (94.57 lbs) whereas you would need 870 lbs of 5-10-10 (Yikes !!!)

In summary:
- At time of seeding/early spring, you can use a balanced fertilizer such as 5-10-10, 10-10-10 or atleast make sure that your fertilizer has SOME phosphorous (P) and potassium (K) in the bag (29-3-4). Grass does not need a whole lot.
- Once the grass starts to grow actively, and you mow the lawn, nitrogen is the most important. Fertilizer with a high nitrogen fertilizer (even Urea 46-0-0).
- to find out how much to apply divide the number "100" with the first number on the bag (N) to get the lbs per 1000 sq feet lawn area (e.g. a 5000 sq feet lawn area using a 10-2-6 fertilizer woudl require 100 / 10 x 5 = 50 lbs of fertilizer to cover the entire lawn). For acres, use the number "4350".
- Generally, if you buy in bulk and have a large lawn, it pays to buy the highly concentrated fertilizer mixes (28-0-0, 33-3-3, 46-0-0) as less product is required (more concentrated) and especially Urea is much cheaper per lb.
However, make sure you distribute evenly.

If you dose your fertilizer according to above rules you will not damage the tender sprouts.


I hope this helped you.
-- Kenneth

P.S. here is an interesting example:

Despite the advice from the garden center, it does matter if you use a 20-27-5 or a 5-10-10. The 20-27-5 is 4 times as concentrated as the 5-10-10. This could affect the total price.

Example:
A 20,000 sq feet lawn

Number of lbs required using 5-10-10: 100/5 x 20 = 400 lbs
(a 10 lbs bag for $22.95)
Price per lb: $2.95. Total price 400 x 2.95 = $1,180

Number of lbs required using 28-27-5: 100/28 x 20 = 71.4 lbs
(a 40 lbs bag for $358)
Price per lb: $8.95. Total price $639.03

In the above (made up) example, although the 28-27-5 fertilizer costs much more than the 5-0-10 (3 times more per lbs and a big investment per bag) the price to cover the 20,000 sq feet lawn with enough nitrogen to make it grow adequately is almost twice as high using 5-10-10 compared to 28-27-5.

Don't be fooled by prices. Calculate the costs based on the formulas given.