Will I kill my window box plants with Miracle Gro?

April 19, 2013 11:03 AM

Now that I have a balcony, I wanted a little garden out there with window boxes. I purchased window boxes and a bag of Miracle Gro online. I already had two potted flowers that were about to burst from their pots. (I was going to buy more tomorrow after the boxes arrived and I had an idea how much room I would have.) The Miracle Gro arrived and despite no warning on the website, it says "Not for use in containers." Will I kill my flowers if I go ahead and use it?

I've ordered another bag of organic potting mix (I should have used Ask sooner I guess, but, as I said, there was no description on the site saying this was JUST for lawns just soil for flowers and plants, which is what I was going to plant in the box. Le sigh.) I've temporarily mixed the Miracle Gro with the soil from the pots and planted the flowers in the window box. The potting soil arrives Tuesday. Will it be ok if I mix the Gro with the potting soil or should I should just give it to my mother upstate and order a ton of potting soil?

(PS any general balcony garden advice-it's a very small balcony-is welcome as my only experience gardening is in the country.)

posted by miss-lapin to Home & Garden (11 answers total)

In my experience, once should be fine...the reason you don't want to KEEP fertilizing containers is that the excess doesn't wash AWAY...ie there's nowhere for it to go and it builds up to toxic (for plants) levels...how much did u add?
posted by sexyrobot at 11:16 AM on April 19, 2013 [1 favorite]

Best answer: The internet seems to be of the opinion that garden soil is contraindicated because it's too dense and heavy, and so doesn't provide enough drainage. Potting soil doesn't pack as well as garden soil, and has more space for water to get down to the roots/drain out. Your plants can get root rot otherwise, among other problems.

There are various remedies on the web, and they all seem to involve mixing something else (lava rocks, soil-less mix, potting soil) in at some ratio or another.

One suggestion, relevant to your situation, gives a 2:3 ratio of garden to potting soil.
posted by Poppa Bear at 11:18 AM on April 19, 2013 [1 favorite]

Best answer: Generally, potting mix is for container plants and soil is in the ground. Soil won't allow adequate water and airflow in containers.

That said, I've had no problem with extremely diluted miracle gro for containers.
posted by wongcorgi at 11:27 AM on April 19, 2013 [1 favorite]

The reason Miracle Gro is for gardens (though they also make potting mix) is because they fortify it with fertilizers and all kinds of things with the assumption that it will spread out over a larger area and dilute itself and excess will run out with watering and evaporation. Putting that stuff in a single pot may overwhelm the plant contained within it and since there's nowhere for those things to go, it basically ODs.

Get some potting soil.
posted by softlord at 11:31 AM on April 19, 2013

Best answer: I've always used it in my containers, in spite of the warning, and as long as you don't use too much it should be fine. Never had a problem and it made them grow like crazy!
posted by Eicats at 11:53 AM on April 19, 2013 [1 favorite]

Best answer: It's fine. I've used it in my containers for years. If you're worried, use it at half dosage. Also, make sure that the container is at least slightly moist before you add fertiliser to it. Otherwise, the roots can be burned by the molecules in the soil. If there's enough water, the molecules dissolve and the plants can handle them properly.
posted by Solomon at 12:01 PM on April 19, 2013 [1 favorite]

Use the instructions for continuous feeding of houseplants.
posted by jgirl at 1:37 PM on April 19, 2013

I too use Miracle Gro for my houseplants (in containers).
posted by Lynsey at 2:42 PM on April 19, 2013

Is it a bag of miracle gro garden soil or miracle gro fertilizer? If it's the miracle gro garden soil, I wouldn't use it in pots. You want container mix, or you want to mix in an equal amount of milled peat with the garden soil to allow for drainage.

(Also I find the miracle gro moisture control container mix to be much better that the regular container mix, though a bit higher in cost.)

If it's the miracle gro fertilizer, go ahead and use it for containers.
posted by release the hardwoods! at 3:53 PM on April 19, 2013

I've done this in the past with no problems as long as the soil has good drainage.

In the future if you decide to use only a non-fertilizer added soil I have had good luck in potted plants with Osmocote.
posted by emypocu at 11:35 AM on April 20, 2013 [1 favorite]

Response by poster: Just so you know, I mixed the miracle gro with potting soil. The flowers are ok (some died thanks to aphids despite my rather aggressive attempts to wipe the little buggers out) but the herbs are indeed flourishing like I can't believe! The sage, thyme, basil, and verbena are such that I'm constantly looking for new recipes so I can thin them out. Thanks metafilter!
posted by miss-lapin at 2:15 PM on July 31, 2013