Cat Grass - Growing Kit - Standard and Wide Mouth Canning Jar

This is a set of models to grow cat grass hydroponically in a standard or wide mouth canning jar.

Want to keep your new cat grass upright, despite your cat's best efforts? Check out this companion print - Base for a Canning Jar

Non-printed Parts

• cat grass seeds
• water
• standard or wide mouth jar - models fit standard Kerr/Ball jars
• jar lid ring or print your own
  • NOTE: standard metal rings eventually rust

Printed Parts

• jar adapter
• seed grate
• top grate lid

Instructions

1. press-fit seed grate into the bottom of the jar adapter
2. put assembly into jar
3. add cat grass seeds to just cover bottom of grate in 1 layer
4. fill water to just touch bottom of seeds
5. mist seeds thoroughly
6. install top grate lid
7. install jar lid ring
8. …wait
9. only add water if/when water level reaches below half and fill back to roughly half
10. after ~2.5 weeks, toss what’s left and grow a new batch

*NOTE: I am not an expert in hydroponic growing, so take the above with a large grain of salt.

Print Settings

• Material:  PETG recommended.  PLA works, but avoid matte or rough surface finishes that can be difficult to clean effectively.
• Supports: none
• Brim: not required on machines with calibrated first layer/good bed adhesion
• Nozzle: 0.4mm
• Layer height: 0.2mm

Updates

12/12/2023

I have had a great deal of success with standard wheat grass seeds.  They seem to sprout more consistently than the oat grass or the “cat grass” seeds I've had and my cat doesn't seem to notice a difference.

Also, I have found I get higher yield sprouting the seeds outside the jar.  I put the seeds in a soaked paper towel between 2 plates for a ~2days, then transfer them into the jar.  It is totally possible to sprout seeds directly in the jar, but not as high of a yield.

9/16/2023

• add standard mouth sized models
• fix orientation of wide mouth models for printing
• add print files for standard and wide mouth kits

I have found the most reliable way to germinate the seeds is to do so in a very damp paper towel until root starts appear on a majority of the seeds.  Then move the seeds into the mason jar.  Keeping the seeds damp for 1-2 days without submerging them is very dependent on air temp/humidity.  So, I have switched to the soaked paper towel method to get more reliable yield even though it is an extra process.

6/29/2023

I am working on updating instructions and the top grate model.  Should be updated in the next week or so once I get some success on the changes.

Models

• our cat pulls the grass right out the top grate, root and all.  He loves doing it, but he doesn't actually eat the grass after he has pulled them out.  So, I will be updating the top grate model to be narrower.

Growing

• I have been growing “cat grass” that is in fact oat seed, so my experience may differ from yours.
• submerging seeds is unnecessary, and from my testing has caused a very high failure rate of the seeds.  I am testing a couple methods:
  • damp paper towel germination outside the jar for 24, 36, 48hrs
  • testing an updated method of spraying seeds and fill water to just touch seeds through grate, then don't touch ever. Unless and until the water level is <half and then fill back to half (still learning how the Kratky method of hydroponics applies here)
• Kelp nutrient solution - inconclusive impact and I am having success without kelp nutrients, so I won't be recommending for now until I have more testing
• our tap water (through a faucet filter) seems to be working just fine.  I have not tested it for PH or whatnot.
• daily misting seeds has caused fungus to grow and doesn't seem to have a positive impact on growth, so I won't be recommending for now.
• even when I have a full jar growing the grass, not all seeds are sprouting.  I attribute this to too many layers of seeds overcrowding, but needs more investigation.