Crabgrass is an annual weed which invades lawns all over the country every summer. No matter how thick your lawn, crabgrass always seems to able to rear its ugly head. A lot of homeowners are trapped in what seems to be a never ending cycle : you spray it, some of it dies, some of it powers through, and the following year the problem is worse.
Effective control of annual weeds like crabgrass is only possible if the seed cycle is broken. Pre-emergent herbicides are designed to do just that: prevent the seed from turning into a viable plant. Pre-emergents work by creating a shallow “barrier” in the soil that the germinating plant must go through to reach the surface. It is important to realize that pre-emergent herbicides do not prevent the seed from germinating, they kill the germinating plant thus depleting the seed bank.
There are various pre-emergent herbicides available to homeowners, many of which can be found at your local home improvement stores. Two of the most popular (and effective) pre-emergent herbicides are dithiopyr and prodiamine. Proper application of either will provide nearly 100% control of most annual weeds, including crabgrass. Prodiamine has the advantage that it does not leach and does not begin to break down until the soil warms up, which means it can be applied early in the season and provides long lasting control (up to 8 months with one application). For this reason, it is my pre-emergent of choice.
The effectiveness of pre-emergents is highly dependent upon timing and proper application. Observing the following rules guarantees success and a weed free lawn for the year:
- Since pre-emergents do not affect plants which are already established, the pre-emergent barrier must be in place before the seed germinates. Pre-emergent must be applied when soil temeperatures reach 50 degrees @ 4″, or when forsythia plants bloom.
- Even and complete coverage is crucial. Missing spots during application will cause “holes” in your barrier where weeds can germinate and produce more seed for the following year. A good backpack sprayer will help you get good coverage with minimal effort, but for smaller lawns even a 2 gallon pump sprayer will do the job.
- Most pre-emergents require watering in within a short period of time. Applying before a rain means Mother Nature can do that part for you, or you can irrigate immediately after application per label requirements.
- More is not better. Applying too high a rate can cause damage to your existing grass roots and also extend the pre-emergent into your overseeding window (if applicable), meaning none of your grass seed will grow.
- Avoid applying pre-emergent during periods when your lawn is stressed. It can make things worse.
- Follow all instructions on the product label and maximum yearly application rates.
A good pre-emergent plan is the foundation of any great lawn. It guarantees a weed free lawn and helps your grass thrive. Master it, and the grass will always be greener on your side.
Recently the popularity of organic fertilizers has been on the rise. More and more people use cracked corn, alfalfa or soy bean meal as their main source of nutrients for their lawn. Proponents of organic fertilizers often claim that the use of organic fertilizers brings has great benefits. Let’s analyze each claim:
- Hard to overdose vs. synthetic. This is true. While application instructions on fertilizer bags are generally clear and easy to follow, some novices may feel more at ease knowing they can’t really over-apply and hurt the lawn. Synthetic fertilizers are fairly forgiving as well though, I have applied synthetic fertilizer at double the rate with no ill effects except to my back from all the extra mowing.
- Slow release. This is also true. Organic fertilizers have to be broken down by bacteria before nutrients becomes available to the plant, resulting in a slow trickle of nitrogen. However, synthetic options such as coated urea and UMAXX exists at a cost up to 7 times lower per pound of nitrogen.
- Feeds the soil microbes. This is true, but the need for an over-inflated microbial population in the soil beyond what grass clippings and bugs and normal natural processes can sustain is unclear.
- Increases organic matter/improves soil structure. This claim is false. Studies have shown little to no long term contribution to soil organic matter content from materials applied on the surface. In pastures studies have shown grass roots to be the major contributor to organic matter – up to 80%. Other studies have show shoot restitution programs to have zero or negative effects of soil organic matter.
- Safer for kids and dogs. This claim is also false, both are equally safe. No child is going to pick granules of fertilizer out of lawn, and if they did, it’s unclear which one would be worse, a granule of urea or a piece of rotting corn coated in bacteria and fungus.
Organic fertilizers do come with some clear disadvantages over synthetic fertilizers:
- Cost. Organic fertilizer is up to 11 times more expensive per pound of nitrogen than urea and up to 7 times more expensive per pound of nitrogen that coated urea.
- Cumbersome. It takes 13-20 pounds of organic material per thousand square feet vs 2 pounds of urea per thousand square feet to apply one pound of elemental nitrogen. That can literally add up to truckloads of corn per year for larger lawns.
- Slow to act. Since the organic matter has to be broken down by bacteria and fungi before nutrients become available to the plant, it takes a while before you see any results, generally 3-4 weeks.
- Unpredictable. No one can say for sure when the nitrogen is going to be available to the plant. Availability of nitrogen also changes with temperature since bacterial activity slows once it gets cooler.
- Unsustainable. Plant derived organic fertilizers are the equivalent of using a gas engine to power a generator which is then used to release hydrogen from water through electrolysis which is then burnt to power a car via steam. Also, a lot more carbon is spewed into the atmosphere for the production and delivery of 20 pounds of corn than for the equivalent 2 pounds of urea.
So with very little benefit backed by mostly anecdotal evidence and a lot of disadvantages, what place does organic fertilizer have in the average lawn? There are situations where organic fertilizers are needed, such as fertilizing an area where nitrogen runoff must be avoided. For most homeowners, synthetic fertilizers work faster, are less work to apply and are significantly less expensive than organic fertilizer. Give your grass the nutrients it needs and the grass will always be greener on your side.