Water and Nutrients

Your plants need to consume water and nutrients to live, and you have your choices

Water

Your plants need water to grow and it makes up a large portion of their final weight. The important things about water are that:

It is within a reasonable pH range (5-7)
It is not too concentrated with impurities
None of the impurities are at toxic levels

In practice:

Reverse osmosis, and distilled water are fine without adulteration, except perhaps pH adjustment (check with test strips or a meter)
You should let any chlorinated tap water sit out for a day to out-gas most of the chlorine
Rain water can have wildly varying pH and impurity levels, so testing with pH strips would be advised as minimum requirement.
Additionally, if you live in an area near active volcanoes, the the rain water that filters through the ash/sulfur cloud is toxic if applied to the leaves, and probably acidic.

Most nutrient blends specify (generally in the small print) the expected hardness of the water they mix with. The hardness instruction refer to assume that most of the hardness is calcium-based. If your water is hard but lacks calcium, be sure to supplement.

Home made nutrients: Compost

Picture of a composting bin — Composting bin

Making your own compost at home is pretty easy and it the cheapest fertilizer you can get. The simplified method is to dump your food scraps, yard waste, and other organic matter into a pile and mix it occasionally until it decomposes. In practice, there are a few things you need to do to make this effective:

Don’t try to make it very rich by adding mostly food. You will get a fowl-smelling pile of maggots and then flies. Keep it mostly slowly-decomposing things like grass clipping, coffee grounds, the ends of onions, etc. Meats should not make up a large portion of the mix as they will attract pests.
Turn it once a month to aerate and accelerate decomposition.
Use a composting container to contain the smell and make it easier to turn.
It takes about 90-180 days to get it decomposed enough to use.

Once your compost is ready, you can spread it directly on top of the soil (also known as top-dressing), mix it with the soil directly, or put it in cheesecloth then put that in water to make compost tea. This tea is great for hydroponic use, but be aware that it is filled with bacteria (almost certainly the good kind) and that will limit the applications in hydro to systems that tolerate a rich microbial flora.

The resulting compost is not super concentrated, but because of this it will be enough for almost any plant. Don’t be afraid to over do it on mature plants (you can probably grow your mature plant in 100% compost if the texture is right), but younger plants would prefer lighter feed.

Organic

Organic nutrients are derived from living things that have been decomposed and broken down using any number of methods. You can use them to supplement your own compost, or replace it entirely with convenient formulations that have been tested to have what your plants need.

If you are supplementing (that is, you are growing in a nutritive soil and need to boost the feed), we use Down To Earth fertilizers for Organic grows. They are reasonably priced and effective. Full disclosure, their availability at our local hardware store factors heavily into this decision. Be aware that they will release slowly, so be gentle in application. I would generally use the all-purpose mix for most grows, and the flower mix as a bloom booster.
If you are going hydro and need a pre-made tea, General Hydro’s Organic Go Box is the easiest entry into growing and contains all the supplements you need. It does not come with pH test strips or liquid. Since this is key in hydroponics, at least pick up some test strips or a cheap pH meter… or better yet, a good one.
If you’re growing higher value crops, most growers swear by Fox Farm nutrients. They are very high quality, and have reasonable concentrations for an organic feed.

Inorganic fertilizers

If you want fast growing and don’t want everything smelling awful, inorganic is the way to grow.

You should get the 3-part General Hydro Grow Kit. It has pH test liquid, supplements, everything you need for most grows, and is compatible with pretty much every system in existence.
By far, far the easiest way to get into hydro is to buy a liquid, one-part feed. We use General Hydro’s Flora Nova series. The grow for leafy plants (or strong vegetative growth), and the bloom for flowering plants.
If that seems expensive (spoiler: it is), General Hydro’s dry mix is the way to go. Shocking no on in naming convention, MaxiGrow is for leafy plants, and MaxiBloom is for flowering plants. While these are 80% of what we use, they are notoriously difficult to dissolve. I recommend 1 tsp per 3 cups of near-boiling water in a quart container, and shake over the period of an hour. Also, they are completely unbuffered, so pH swings are not unusual. Test daily.
Want to split that difference? Veg+Bloom makes a great fertilizer that contains more than the bare minimum of trace minerals. They are more expensive, but dissolve… better, I guess? That said, it’s buffered, and not prone to pH swings. We’ve had great luck with all plants in this… but it’s, you know, 3x the price of MaxiBloom. So, for small grows, it’s worth it for the convenience.

Next Steps

You have concluded our basic articles and are ready to take on the world. Perhaps try your hand at growing some chilies? Maybe taking it easy with some indoor herbs? In any case, let us know if you feel like you want to know more.