My husband said something quite shocking to me this week:
"Honey, I would like to put fertilizer with pre-emergent weed killers out at the right time this year. I'd like to get ahead of things this spring."
Since this behavior is quite unusual, I decided to get all of the facts about spring fertilization so when he's ready to jump in the truck and buy the stuff, I'll be able to give him a list. We always question our sanity, however, sometime in the early summer when we're mowing like crazy, wondering why we fertilized earlier in the season.
I got out my Master Gardener's notebook and checked out the section on fertilizing. I chuckled at all of my notes scribbled in the margins. I obviously felt we needed the class on fertilizers around our house.
When purchasing fertilizer, you'll notice a number grade on bags of "complete" fertilizer (it's complete when it contains each of the three major plant nutrients). The numbers represent nitrogen, phosphorus and potassium. Different combinations are right for different times of the year.
What do the numbers mean? A grade of 10-10-10 would mean a ratio of 1-1-1 of the three elements. A grade of 5-10-5 means a ratio of 1-2-1. Grade 12-4-8 means 3-1-2 and so on.
These macronutrients aid different parts of the plants. For instance, nitrogen is good for foliage growth. An excess of nitrogen makes spindly plants with few fruits. A deficiency results in reduced growth, yellowing and reduced lateral growth. Phosphorus is good for the roots. Potassium (potash) is good for buds, flowers, fruits, as well as for cold-hardiness, disease-resistance and general durability.
So in the spring, most people use a fertilizer that's high in nitrogen. But be careful of too much nitrogen, as the early top growth "typically comes at the expense of your lawn's roots, and during wet spring weather, an overfertilized lawn can be especially vulnerable to lawn fungus," according to Dawn West of Oregon State University.
A good answer to this is a fertilizer with slow-release nitrogen, which provides your lawn with controlled, steady nutrition over a longer period of time. The best time to apply is when the grass is damp so the product adheres to the leaves.
There's an old gardener's tale that says to spread pre-emergent weed killer when the redbud trees start to bloom. Basically, you want to get the stuff on your lawn after the last frost and before the weeds germinate.
If you add 3 pounds of nitrogen per acre to your lawn, in addition to encouraging healthy spring growth, it will digest your thatch. Do this before April 15. A calendar from the West Virginia University Extension Service suggests crabgrass control by April 12, and pre-emergent landscape weed control by April 25. Be sure to use a spreader for accurate application.
If you are seeding any part of your lawn, don't use the pre-emergent weed killer. It'll prevent the grass seed from germination as well.