All posts by trish

About trish

I'm a 26 year old PhD student doing research in the use of Semidefinite Programming in solving QPCCs (Quadratic Programs with Complementarity Constraints). There often isn't information available about the specific problems I'm facing, so when I figure things out the hard way I'm going to blog about them in hopes that some future googler might find them helpful. In the same spirit, I'll probably post about other interests sometimes, again with the goal of providing information on topics that could use more coverage.

Hydro workshop: Support

Hack 1

Hack 2

Hack 3

(and a more proper model studied later in the case studies)

Hydro workshop: pH and EC/TDS


pH can be measured with colour changing papers or liquids, or by electronic meters.

pH is important because it effects nutrient absorption. Here’s a graph showing availability of nutrients in hydroponic applications at different pH levels (width of band represents availability).

pH gradient

Continue reading Hydro workshop: pH and EC/TDS

Hydroponics workshop: Net cups and grow bags

Net cups:

Net cups are plastic cups with holes on the sides and bottom. They’re used in many hydroponic systems to suspend a plant over a nutrient solution so that the roots dangle in the solution. The hole to plastic balance is important.  Holes should be:

  • plentiful enough that roots can exit the cup easily
  • small enough that media isn’t falling into the solution
  • large enough that the plants roots won’t get choked as they grow

Net cups are sold in hydroponics stores in a few standard sizes:

  • 2″: sufficient for smaller plants like herbs or for ground level plants like lettuce.
  • 3.5″: can work for tomatoes, peppers, etc.
  • and larger baskets

As a general rule, you can get away with a smaller net cup if you will have good support, and you can get away with less support if you have a bigger net cup.

Improvising net cups from household plastics like yogurt cups, pudding cups, etc:

  • Clean it inside and out with water and a little bleach, but then rinse very well to remove all residue.
  • Choose safe plastics that have a well-defined ‘lip’ and don’t crumple or tear easily.
  • Use an X-Acto knife to cut holes or burn holes with a soldering iron (but ventilate the area well!)
  • Completely remove any paper or glue residue, it’ll cause mold later! 🙁
  • If your holes are a little too big for your media, you can line the cup with plastic netting.  (I’ve tried cheesecloth before, it held media well but decomposed quickly and introduced mold to the system.)


 Grow bags:

These are commonly made from landscaping fabric, which is a fabric designed to breathe and let water through while being impenetrable to roots.  They’re easy to make with a sewing machine.  Using grow bags, the bag is filled with media and the whole root system lives in media, unlike with net cups where only the base is in media and the lower roots dangle in air and/or water.

Plants in grow bags benefit from air pruning, so they develop short, dense root systems and can be very well rooted even in a relatively small bag.

Hydro workshop: Nutrients and supplements

NPK and micronutrients

The three main nutrients every plant needs are NPK:

  • Nitrogen (N): promotes vigorous, lush green growth
  • Phosphorus (P): healthy roots, also key for metabolism and transition into fruiting phase
  • Potassium (K): good water management, robustness against temperature, drought, disease, insects

All necessary, but ideal strengths vary by plants and by phase of growth. Other micronutrients are also needed in trace amounts, but any purchased nutrient solution system will include them.

Continue reading Hydro workshop: Nutrients and supplements

Hydroponics workshop: Rooting medium

Although plants in hydroponic systems do not need to take their nutrition from soil, soil in traditional gardening serves other purposes which must be taken into account:

  • Protecting the plant’s roots from the elements and hiding them from bugs and animals,
  • Giving the roots something to grip onto, which allows the plant to hold itself upright,
  • Temperature control,
  • Keeping the right amount of water and oxygen near the roots.

To serve generally these same purposes, we provide plants with a rooting medium, commonly called the media or substrate. Continue reading Hydroponics workshop: Rooting medium