Here is a patent of charcoal as hydroponic substrate. How can the owner practically protect his rights against infringement by private gardeners? Will he go around looking into people's pots and then sue them? And even if he does - what kind of damage can he claim? The estimated price of the charcoal that he would have sold to the infringer for the purpose of his hydroponic farming?... There are no companies that would sell charcoal for hydroponic gardeners as everybody can produce it easily alone. Can he sue companies that sell generic hydroponic systems/pots and mention in their manuals charcoals as one of many possible hydroponic media?
The link provided didn't work so I searched and found US8544207B2. It should be noted that this patent does not claim the use of charcoal as a hydroponic substrate. Instead it claims activated carbon fiber. Specifically carbon fiber derived from bamboo. I don't think this is something you can just pick up at the local Home Depot. If you want to use regular charcoal in your garden, this patent won't stop you.
Given that activated carbon fiber is not a commonly available material to the general consumer, I don't think the inventors have much to worry about with respect to home gardeners. You can find it, but generally sold by companies to other companies in the filtration business.
Which brings us to you question about claiming infringement against home gardeners. As I said, I don't think this is an issue with this patent. In any case the patent has expired for fee related reasons. Generally this is because the patent owner finds the value of the patent to be less than the required fees. If we ignore the situation with this specific patent, it is possible for a patent owner to sue end users. Generally the idea is that although they don't realize any useful return on the specific person they are suing, they can take a win in such a case to threaten other end users. Since paying a reasonable licensing fee is much cheaper than fighting in the courts you might derive some useful income from just sending threatening letters. I believe such a strategy is pretty rare, but I found one similar case.
Besides inexpensively going after many end users as EricS answers, another approach is to look for suppliers of the (non-infringing basic product) who promote the use of it in an infringing process. They might do so by advertising, application notes or consulting with end users.
The manufacturer or distributor isn’t performing the method steps, so no direct infringement, but if it is actively facilitating and encouraging others to perform those steps, this is indirect infringement.
35 U.S. Code § 271 - Infringement of patent (a) Except as otherwise provided in this title, whoever without authority makes, uses, offers to sell, or sells any patented invention, within the United States or imports into the United States any patented invention during the term of the patent therefor, infringes the patent.
(b) Whoever actively induces infringement of a patent shall be liable as an infringer.
At least one actual entity must be shown to be directly infringing or indirect infringement can’t be established. But the patent owner does not need to sue any direct infringer, just prove that at least one exists.