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Phosphorus used in gardens can contribute to algae blooms in lakes, like this one in 2012. Photo: Lake George Waterkeeper
Phosphorus used in gardens can contribute to algae blooms in lakes, like this one in 2012. Photo: Lake George Waterkeeper

For lawn and garden: the do's and don'ts of fertilizing

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It's illegal to fertilize a lawn with phosporous in New York State. The Department of Environmental Conservation sent a press release around last week with that reminder (more information on this here.

There are exceptions, dependent on a soil test. Cooperative Extension horticulturist Amy Ivy has lots of good information this week about that, and about fertilizers and fertilizing in general.

Top takeaways: don't fertilize your lawn till September anyway; do fertilize vegetables if they looked peaked; do fertilize flowers; don't fertilize woody herbs like thyme, sage and such; and as always, know your soil. Here's more information from Amy Ivy.

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Reported by

Martha Foley
News and Public Affairs Director

Martha Foley: Could you sort out what’s illegal and what’s not here?

Amy Ivy: Yeah, well, the idea is that lawns don’t need that much phosphorous and so if they don’t need phosphorous, don’t put on a fertilizer that contains it. It’s all part of trying to keep the excess phosphorous out of the lakes. That’s what leads to the algae and the algae blooms in the lakes.

MF: So that’s just overdosing with phosphorous, right?

AI: Right, so it’s not necessary. So whenever you look at any fertilizer, whether it’s for your garden or your lawn or anything, there are three numbers. The classic is 10-10-10, 5-10-5, there those kinds of three numbers. And the middle number is phosphorous.

MF: Hm, Ok.

AI: So most lawns, they need a little bit when they’re getting started from seeds. And then usually they don’t, so what the law says is have your soil tested and if the test indicates that your soil needs phosphorous, then you can get a blend that has phosphorous in it. Otherwise, just leave that out completely.

MF: So you’d get a something-zero-something fertilizer.

AI: Yeah, and they are finally starting to carry that. The industry has caught up now with all this. So it is widely available and often it’ll be labeled at such; now they’re starting to promote the zero phosphorous fertilizer. And Cornell has adapted a test to make it as easy as possible for homeowners. It costs, I think, $8. It’ll test for phosphorous and pH, those are the two key things to think about with your lawn. So it’s a simplified test, so it’s easy to do, and now is not the time to fertilize.

MF: I was just going to say! Yeah, why did they put this press release out now?

AI: I have no idea.

MF: Because I know, we have this conversation every year, now is not the time to feed your lawn.

AI: Exactly, do not fertilize your lawn right now. But maybe it’s to get ready because September is the #1 month of the year, that’s the big month for lawns. That’s the month to do anything to your lawn; overseed it, reestablish it, fertilize it, core aerate, anything of that.

MF: Now is just the time to be mowing it all the time. Constantly mowing.

AI: Yeah, I tell you, the people who have finally adapted the mow high, three inches at the shortest, even four inches, they have become believers that your lawn will be so much greener if you just keep it higher. That doesn’t mean never mow it, but set your mow deck really high and if it’s a really hot, sunny day, don’t mow that day because, watch, you’ll go from a green lawn and it’ll just turn brown within a few hours. So it’s very stressful to lawns on those hot days, so mow them as little as often in the summer and when you do mow, set your mower as high as you can.

MF: So now is not the time for lawns, be gentle with the mowing and all that. So I got thinking about fertilizing other things because everything is growing so fast now; the weeds, the vegetables. I mean, everything must just be sucking all the good stuff out of the soil. Is it time to fertilize in the garden?

AI: Right around the 1st of July is a really good time to kind of take a look because the month of July is, you’re absolutely right, that’s when the tomatoes are ripening and the pumpkins are sizing up and the flowers are at their biggest and most bodacious time. So yeah, they are using up food like crazy. So having it available, so when the plants need it, it’s there, rather than wait until they start to look hungry and then try to correct that.

So yeah, definitely, if you’re going to fertilize, now until late July is a good window. After late July, you really don’t need to fertilize things that you’re going to be finishing off in September. So, you know, the tomatoes and your summer crops, after late July they really don’t need it. And then the annuals, and the things that are going to go with the frost, you really don’t need to fertilize them after July.

MF: Okay, so here’s my particular question; because I mulched my garden pretty heavily, you know, in my neverending attempt to keep it moist and weed-free, so I have heavy mulch over everything, how do I fertilize this stuff?

AI: Well, there are a couple ways. It depends how big your garden is and if your garden even needs it, too.

MF: It’s small.

AI: It kind of depends of how you’ve managed your garden; if you worked in a whole bunch of compost and now this mulch that you’re using is decomposing and the plants look great and really dark green and that kind of thing, maybe they don’t even need it at all.

MF: Okay.

AI: But if you haven’t and your soil is really poor, sandy, and you know, you know, you need to supplement. So, you know, first have that thought go through your head. And then if you decide, I really am going to fertilize, am I going to do it? Then you have two ways. You can either, depending, if your garden isn’t too big (and I know this won’t work for you), but people with smaller gardens, you actually can pull back the mulch a little bit (I know that sounds like a pain, but that’s why it’s a small garden), pull it back a little bit and you can scatter the granular.

It can be a conventional fertilizer or there are a lot of poultry-based organic products that come in a granular form, which are a lot easier to handle. So you can sprinkle that down, and then it would be great if you could water it, and then push that mulch back. So that’s one way. Or you can go with the liquid fertilizer. And, you know, there's conventional stuff all over the place.

MF: Not so much in the organic line, though, right?

AI: There’s some. There’s Fisher mulch, and it’s probably one of the best known. The problem is, as it goes through the mulch, a lot of it’s going to stay in the mulch area, too. If you have a trickle or a drip system set up, you can run some stuff through that. The problem is the organic-based stuff often will kind of clog it up. So you want to be a little careful with that if you do have a drip. Some people have, to conserve water, it’s a really great way to conserve water, some people have set up drip systems. Just be a little aware, take a look at the slurry that you’re mixing and see if it look clumpy and gluey like that, then maybe don’t put it through your drip system.

MF: Well, my drip system is the gallon jug with the never fail nail hole in the corner.

AI: Well, that’s pretty good, that nail hole probably isn’t going to get clogged up too bad. It’s more when you have a lot of tiny pores that the stuff needs to seep through, then the organic stuff doesn’t go through. Then you need to weigh your management plan. Is it more important to conserve water and use the drip, then you might want to you a conventional water-soluble fertilizer. Or if it’s more important to you to be organic, then you would go through the extra effort to pull that mulch back and get the product under. Or work really hard at building up the soil the rest of the year with carbo-crops, green manures, all this stuff so that it has a reserve of nutrients to bank on.

MF: Okay, two quick questions; flowers also, good time to fertilize them?

AI: Yes, because they’re growing full speed ahead, too. They really are pushing out a lot right now. Yes, definitely all the flowers.

MF: And you mentioned that you might now want to fertilize herbs, right?

AI: Oh right, right! Yes, yes, herbs actually taste better— because with herbs, especially the things like thyme and rosemary and sage, you know, the ones where it’s a more concentrated oil that you’re going for, they actually have more intense flavor when they’re not overly lush. So the lush growth actually dilutes because, you know, it’s just more tissue and water and not the essential oil that’s giving it the flavor it has. So it does dilute it some. So they often talk about letting herbs actually suffer a little bit. They get more intensely flavored when they’re not completely lush and full and all that.

I would say that parsley and basil and cilantro would be the exception. Because, you know, you just want those big juicy leaves that you’re going to chop up and eat fresh. But it’s more, as I said, the wiry, like the thyme, and the savory and sage, and things like that.

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