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Plant Project: Design Objectives

by Amelia Greenhall - 02/26/2019

You can read my first Plant Project post here, and Jared wrote about building the first version of the system.

What makes a good hydroponic garden system? One that will actually get used regularly, for a long time, and make lots of plants for not much money. Also, it should be fun, smell good, and the plants should be delicious! This translates into a few design goals:

  1. No Spills
  2. Very Quiet
  3. Ongoing cost of production $1/week
  4. Easy to clean and maintain
  5. Doesn’t take much of your time

No Spills

Don’t flood your apartment (or basement, or garage).

Design:

  • Flood-drain system: The water and nutrients in the lower container pump right above them into an upper container with the plants, and slowly drains back down. — Any drips just go back to the bottom container — the upper container is nested into the lower one. — There are no pipes or seals or connections that happen outside of the bottom container. — The amount of water in the system is always less than the smallest container - so it won’t overflow even if the pump doesn’t stop for some reason.
  • Low center of gravity: with the water/plant tubs on bottom and a short and squat dimensions, the watery part of the system is not going to be knocked or kicked over accidentally.

Quiet

Make barely perceptible and non-annoying noises, if any at all. Shouldn’t interrupt conversation, wake you up, annoy you or your neighbors. It should fade into the background except when you want go grab fresh herbs or tomatoes for dinner.

Design:

  • Flood and drain system choice has advantages here too: instead of water being pumped all the time, the pump only runs twice a day, for a minute or so each time.
  • The fan and water pump are the only moving parts, so the parts selected for them need to be quiet and the sounds should be harmonious and gentle.
  • The lamp fan runs while the lamp is on, which is 14hours/day - so it needs to be very quiet.

Ongoing cost of production less than $1/week

Ideal is to get a 10x or more return on your incremental material costs. By choosing high-value plants like kitchen herbs, tomatoes, or peppers, you could to grow $10-30 worth of food/week for yourself for an incremental cost less than $1/week.

The ongoing costs (after the cost building it initially, which is considered separately) include:

  • Seeds
  • Electricity
  • Nutrients
  • Water
  • Growing medium (rock wool or other seed starting media, and expanded clay pellets, mesh pots)

Each ongoing cost item should be selected to minimize cost and be re-usable when possible. Also, wherever we can, parts and design objectives are chosen so that over time, you can to further reduce the cost to grow plants. For example, saving or trading seeds with other gardeners, or washing and re-using expanded clay pellets.

Easy to clean and maintain

Ideally, once you build it, you hardly ever, or never, have to spend money on maintaining or repairing the physical parts of the system itself. So design wise, this reinforces the decisions to minimize wear parts, moving parts.

Doesn’t take much of your time

Your time is probably the most important ongoing cost of all. This means we want to simplify things wherever possible, so you don’t have to spend your time on it. We should make the main activities easy, and as pleasant as possible:

  • Planting
  • Harvesting
  • Starting seeds

And also focus on the less frequent, but important activities that might put you off track and make it start gathering dust if they’re too hard or intimidating:

  • Changing water and/or adding more nutrients
  • Cleaning
  • Maintenance and repairs

As you get more experienced and have the system going, you can also reduce the time you spend on it.

Next post: Attempting assembly and the Bill of Materials (BOM)

— Amelia Greenhall

plant-project

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