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FAQ: Containers, Potting Soil and Fertilizers

Containers, Potting Soil, and Fertilizers

Please refer to our Seed Starting FAQ for directions on starting seeds.

FAQ: Containers, Potting Soil and Fertilizers

1. Are there any requirements for containers?

2. What should I fill the containers with?

3. How about fertilizer? What should I use and how often?

1. Are there any requirements for containers?

carrot vegetable containerAs far as I’m concerned, there is one absolute requirement for containers for living plants: the container must have drainage holes. No excuses: if you want the plant to live, the container must have drainage holes. Often you can drill holes in containers that don’t already have them. If you have a beautiful container that you really want to use but cannot drill holes in, then you can use it as a “cache pot.” Pot your plant in something else with drainage holes, and set that pot in the beautiful pot with no holes. In this case, be sure to drain the water out of the “cache pot” an hour or so after each time you water.

Otherwise, anything that will hold soil and have enough room for what you plant in it will be OK. Clay (terracotta) pots are cheap and look good, but dry out quickly, are heavy, and tend to shatter from frost in below freezing weather. Plastic can look reasonably good (as honest plastic) or fairly terrible (as fake-something else). Most of my containers are plastic. Wood is lovely but expensive. There are various other materials.

Non-traditional containers include five-gallon buckets, laundry baskets lined with plastic, plastic storage containers, heavy plastic growing bags, dishpans, large plastic bowls, and just about anything and everything else that will hold soil.

2. What should I fill the containers with?

potting soilI’ve looked this up in several container-garden specific books that I own to be certain I’m giving you good advice. Fortunately, the books agree with my own experience, so I am answering this based on my own experience, plus the recommendations of several books.

My first recommendation is a commercial, all-purpose Soilless Mix, often called “potting soil.” One popular brand is “Pro-Mix” and another brand is “Jiffy-Mix”. There are several others and I have used various brands with uniformly good success. These are available at local garden centers. If you want organic potting soil or you cannot find it locally, you can buy it online at Gardens Alive!, Peaceful Valley Farm Supply, or other online suppliers. This is a very, very expensive way to buy it though: local garden centers should be much cheaper. Because I use a lot of it, I buy it in 3.8 cubic foot compressed bales, and store it in two garbage pails on our deck. Smaller sizes are available too.

Garden soil, no matter how good, is not suitable for containers. Purchased “topsoil” (alone) is not suitable for containers either. Both are too heavy, and will compact. Don’t buy potting soil labelled for one specific use either, but get an all-purpose blend.

If you want to, you can add various things to your soilless mix: sand (builder’s or “sharp” sand, not seashore sand), for one. I rarely do, though, but use it “as is.” If you have compost, you can add that (for outdoor containers only). If you can purchase “spent mushroom soil” economically, you can add that to outdoor containers. Here’s a link where you can purchase mushroom soil. I don’t recommend adding *anything* that isn’t sterile to indoor containers. Once you’ve had one infestation of fungus gnats (or other pests) in indoor plants, you won’t want to add anything non-sterile to potting soil used indoors! (Please note that if you add either compost, you’ll need to adjust the fertilizer advice given below.)

The alternative is to mix your own “potting soil” or “soilless mix”. I used to do this before the premixed kind was easily available. It’s bit of a nuisance and I don’t do it now, but it can certainly be done. If you want/need to mix your own, I recommend this mix:

(“Parts” are by volume, not by weight. One bucket of this, one bucket of that, etc……)

One part of peat moss or coir (coconut fiber)
One part of perlite or horticultural grade vermiculite
One part of builder’s sand
One part of purchased and sterile topsoil (this can be omitted)

Other “recipes” for potting soil that also work well are found here..

3. How about fertilizer? What should I use and how often should I fertilize?

container-garden-fertilizersYou will realize, of course, that regular feeding of plants in containers is absolutely necessary. Again, I’ve looked this up in a couple of books. I recommend a two-fold approach (based on the books plus my own experience):

1. Mix a slow-release fertilizer with your potting soil before you pot the plant. “Osmacote” is one popular brand of slow-release fertilizer. Slow-release fertilizers are available at local garden centers as well as online. For organic gardeners, there are slow-release (pelleted) organic fertilizers, including pelleted fish fertilizer and pellitized compost.

2. When the plants are growing, apply a complete, balanced fertilizer, diluted to half strength, once a week. You want to look for the words “complete,” “balanced,” and “micronutrients” on the fertilizer. The three numbers on fertilizers represent nitrogen, phosphate, and potassium (N, P, K). I don’t think the specific numbers are really all that important. You are going to give your plants *enough* of all three main elements. As long as there is *enough*, a little extra of one or the other isn’t going to harm anything. Grossly too much might be harmful but a little too much won’t. And if you apply the weekly fertilizer at half recommended strength, you aren’t going to have grossly too much.

I have used “Miracle-Gro” and other commercial fertilizers (even houseplant food!) with very good results, and I’ve also used organic fertilizers with very good results.

These are the basics. There are various other beneficial additives, such as greensand (a natural mineral with many micronutrients), kelp spray, and a host of others. If you want to do an absolutely superb job with your plants, you’ll probably want to investigate these or some other soil amendments, but they are outside the scope of this article.