Yes - if you want best results from your soil. Some additional reading from an old post: Originally posted in '05: In my estimation, the only case to be made for reusing container soils is one of economics, and you'll never find me argue against making that decision. If you can't afford it, you can't afford it. That said and setting economics aside, you might decide to reuse soil for reasons other than economical. Perhaps the effort involved with acquiring (or making your own) soil is something you might not wish to go through or be bothered with. In any case, it would be difficult to show that soils in a more advanced state of structural collapse can somehow be preferred to a soil that can be counted on to maintain its structure for the entire growth cycle of the planting. So, if the economic aspect is set aside, at some point you must decide that "my used soil is good enough" and that you're willing to accept whatever the results of that decision are. All soils are not created equal. The soils I grow in are usually pine bark based & collapse structurally at a much slower rate that peat based soils, yet I usually choose to turn them into the garden or give them over to a compost pile where they serve a better purpose than as a container soil after a year of service. Some plantings (like woody materials and some perennials) do pretty well the second year in the same bark-based soil, and with careful watering, I'm usually able to get them through a third year w/o root issues. Watering habits are an extremely important part of container gardening. Well structured soils that drain well are much more forgiving and certainly favor success on the part of the more inexperienced gardeners. As soils age, water retention increases and growing becomes increasingly difficult. If your (anyone's) excellence in watering skills allows you to grow in an aging medium, or if your decision that "good enough" is good enough for you, then it's (your decision) is good enough for me, too. The phrases "it works for me" or "I've done it this way for years w/o problems" is often offered up as good reason to continue the status quo, but there's not much substance there. I'm being called away now, but I'll leave with something I offered in reply on a recent thread: "... First, plants really aren't particular about what soil is made of. As long as you're willing to stand over your plant & water every 10 minutes, you can grow most plants perfectly well in a bucket of marbles. Mix a little of the proper fertilizers in the water & you're good to go. The plant has all it needs - water, nutrients, air in the root zone, and something to hold it in place. So, if we can grow in marbles, how can a soil fail? Our growing skills fail us more often than our soils fail. We often lack the experience or knowledge to recognize the shortcomings of our soils and to adjust for them. The lower our experience/knowledge levels are, the more nearly perfect should be the soils we grow in, but this is a catch 22 situation because hidden in the inexperience is the inability to even recognize differences between good and bad soil(s). Container soils fail when their structure fails. When we select soils with components that break down quickly or that are so small they find their way into and clog macro-pores, we begin our growing attempts under a handicap. I see anecdotes about reusing soils, even recommendations to do it all over these forums. I don't argue with the practice, but I (very) rarely do it, even when growing flowery annuals, meant only for a single season. Soils don't break down at an even rate. If you assign a soil a life of two years and imagine that the soil goes from perfect to unusable in that time, it's likely it would be fine for the first year, lose about 25% of its suitability in the first half of the second year, and lose the other 75% in the last half of the second year. This is an approximation & is only meant to illustrate the exponential rate at which soils collapse. Soils that are suitable for only a growing season show a similar rate of decline, but at an accelerated rate. When a used soil is mixed with fresh soil after a growing season, the old soil particles are in or about to begin a period of accelerated decay. I choose to turn them into the garden or they find their way to a compost pile. Unless the reasons are economical, I find it difficult to imagine why anyone would add garden soils to container soils. It destroys aeration and usually causes soils to retain too much water for too long. Sand (unless approaching the size of BB's), has the same effect. I don't use compost in soils because of the negative effect on aeration/drainage. The small amount of micro-nutrients provided by compost can be more efficiently added, organically or inorganically, via other vehicles. To boil this all down, a container soil fails when the inverse relationship between aeration/drainage goes awry. When aeration is reduced, soggy soil is the result, and trouble is in the making." Al

foo foo yuppie carp .. IMHO ... Why you may consider it "yuppie" I have no idea - the recognition of mycorrhizal relationships and the understanding of how they benefit plants has been around for years. Nothing yuppie about it unless one considers being open to relatively recent scientific discussion a yuppie pastime. Might it help to expand your knowledge base a bit more? I didn't think you were so closed-minded, Ken :-) As a matter of fact, the presence of a strong mycorrhizal relationship supports your oft repeated statements that shrubs and trees require "no" fertilizing - generally woody plants that DO benefit from this relationship require minimal fertilization as they are able to access nutrients over a far greater territory than those plants without a similar relationship. And if you had even seen a comparison of a tree root system grown with the benefit of a strong mycorrhizal relationhsip compared to one without, you wouldn't consider it foo-foo -- it is very real, extremely obvious and scientifically documented. Below is a photo of two maple seedlings of the same age. The one on the left was grown without benefit of mycorrhizae, the one on the right with. The difference in root development is startling.......and this is without the extension of the fungal hyphae in the soil that would increase the functional root spread 2-3 times or more.

In the container forum, there is a thread I started that has been ongoing a few days regarding Mycorrhizal Fungi and specifically their effect on container grown plants during hot weather. A condensed version of what we've talked about there: Some ectomycorrhizal fungi that colonize the roots of trees can be found growing in a compost heap, but soil and leaf mold from a forrest floor are better sources of free spores for MF. The endomycorrhizal arbuscular fungi that colonize the roots of grasses and vegatables don't grow except on the roots of plants and will not reproduce in a compost heap. Starting from a sample of soil from very healthy grass roots or a commercial inoculant is the best source to grow them from. The only way to grow them is on the roots of living plants. For small amounts of inoculant for containers or to start growing your own, the cheapest source is Myco-Grow Soluble from Fungi Perfecti. This product is about $8 with shipping for an ounce that will inoculate up to 200 plants when dissolved in water. Many others are available, but this was the best one we could find that had lots of strains of MF and sold it in small quantities for individuals rather than commercial growers. When mixing an inoculant with water to pour on the soil, it is probably best to use filter water, rain water, distilled water, or Chloramine neutralizer in tap water. While the chlorine and chloramine in tap water are neutralized by soil when you water plants and doesn't do much damage to soil microbes below the top inch of soil, dumping the inoculant spores directly into chlorinated tap water may kill many of the spores you've just paid for or collected. Here are two artilces about growing your own MF inoculant http://www.extension.org/article/18627 http://newfarm.rodaleinstitute.org/depts/NFfield_trials/0404/mf_update.shtml Here are two articles from Texas A&M research on containers and MF during hot weather http://aggie-horticulture.tamu.edu/faculty/davies/research/abstracts/pdfs/2005-130-jashs.pdf http://www.hriresearch.org/docs/publications/JEH/JEH_2000/JEH_2000_18_4/JEH%2018-4-247-251.pdf Below is the link to the thread in the Container forum Here is a link that might be useful: Mycorrhizal fungi helps plants survive high temps in containers

Coming from a professional horticulturist, I agree almost entirely with irina :-) Nothing supersedes proper culture and care. Proper heat and light, proper potting soil, proper watering and proper fertilization. Amendments for any kind of houseplants are almost always unnecessary. And in some cases, can be counterproductive. Mycorrhizae is completely ineffective in an indoor container growing situation with a soil-less potting mix. Won't hurt but doesn't help. Save your money :-) Superthrive (aka 'Superjive') is just heavily promoted snake oil. All it contains are some rooting hormones and B1. And you dilute it down to where it is almost nothing but pure water anyway!! B1 is not a necessary plant additive (plants make their own) and a rooting hormone is only necessary if you are rooting. Save your money :-) Kelp or any other organically derived fertilizer is highly inefficient in an indoor container situation for the same reason myco is - no active OM so none or insufficient populations of soil microorganisms to convert it into a plant usable form. Same with humic acid........can be beneficial in an outdoor garden setting but pretty much useless indoors. Save your money :-) And despite all manner of scientific literature to the contrary, the belief that adding Epsom salts somehow makes plants grow better/stronger/faster is a myth that resists being broken. Epsom salts - magnesium sulfate - is only of benefit if you have a magnesium deficiency. Period. And for any containerized indoor plant, that is easily addressed with a full range fertilizer. Save your money. Or save your Epsom salts for the bathtub soak to relieve the sore muscles you got while gardening outside :-))