By Sally McCabe, PHS Associate Director of Community Education 

Benefits of Combining Hydroponic Gardening with a Windowsill Herb Garden 

Every winter I succumb to more than a touch of cabin fever. I MISS MY GARDEN! With that comes the craving for green things to see, to smell, to touch, and even to taste. My space quickly fills with houseplants and blooming bulbs; I can see and touch and maybe even smell, but I’m probably not going to eat any of that. 

What about a windowsill herb garden? It checks all the boxes: fresh! green! tasty! healthful! In years past I have planted small pots and window boxes of mixed herbs from seed (thyme, cilantro, oregano, mint, and some chives in the corner) indoors. Everything came up eventually and grew for a little bit. But I always forgot to water somewhere along the line, and plants stretched toward the inadequate sunlight. I also got soil gnats. RIP herbs. 

What if I could hire a robot to automate all of that for me? 

Enter the indoor hydroponic unit. It feeds, waters, has its own lights, and fits just about anywhere. 

So I started looking into small indoor hydroponics--compact systems designed to grow plants without soil, typically using water-based solutions enriched with nutrients. They feed, they water, they fit just about anywhere. The ones I interviewed had their own light units, which meant I could put them anywhere, so I could still share the windowsills with the cats. 

Here’s what I found when I started doing my homework: 

Hydroponic setups are a lot like inkjet printers; you invest in a quality setup, and then you're constantly buying supplies—like nutrient solutions for the hydroponics or ink cartridges for the printer. The ongoing cost can be surprisingly high!  

Facebook Marketplace had about a gazillion setups available for pretty cheap. Not all were new, and I got the impression that people bought them, played with them, changed their minds, traded up, and tried out new ones. Eventually, you give up or find the perfect setup for your physical situation or lifestyle.  

Let’s walk through the steps so you can find what best fits your requirements. But first, what are the advantages, and what are the challenges? 

Pros of Indoor Hydroponic Gardening

• FUN! 
• Space Efficiency: Grow in teeny tiny spaces. 
• Faster Plant Growth: Plants receive direct access to water, nutrients, and oxygen. 
• Water Conservation: Use significantly less water because the same water gets reused over and over 
• Year-Round Growing: Enjoy fresh, homegrown produce no matter the season.
• Cleaner Harvest: No grit in your spinach. 
• Less Need for Pesticides: People keep telling me this, but I’ve yet to see it prevent aphids & mealybugs. But yes, less soil gnats.

Cons of Indoor Hydroponic Gardening

• Steep Learning Curve: You need to do a lot of homework before committing, because of the cost. 
• Initial Cost: It can be expensive, especially if you’re buying a pre-made system, lights, or pumps. 
• Maintenance: They need regular maintenance to monitor water levels, pH balance, and nutrient concentration.  
• Electricity Dependence: Power outages suck.  
• Space Constraints: Most systems are space-efficient, but they can still be limited in the number and size of plants they can support; nothing quite like paying $150 for a setup to end up achieving one salad per month. 

Hydroponic Garden Options for Your Windowsill

Here’s what you need to consider before you make any big decisions:  

• Do I have enough room? This will influence what size system you choose. 
• Do I have to share the space with others (people, kids, cats, houseplants with seniority)? 
• Do I have sufficient light, or will I need to have that be part of the system? 
• Will I need electricity? Are there grounded outlets nearby? 
• Is a windowsill really the best place for all this (too cold, too near heat, etc.)? 
• How much time and patience do I have to give to maintenance? 
• How deep is my pocket? 

Different Kinds of Hydroponic Gardening Systems 

• Sweet Potato in a Jar (practically free): Really, really passive system. Plants subsist entirely on water and whatever food they can produce or have within.  I’ve had sweet potatoes last for over a year, pumping out miles of vine and leaves which, surprisingly, are edible. Requires topping off and occasional root washing. If you can handle this, move on to sprouting seeds. Again, no nutrients needed. 
• Wick System (cheapest, ideal for beginners): This is a simple passive system where plants draw nutrients through a wick from a reservoir. It doesn't require pumps or electricity. Think of a kid project with a garden in a 2-liter bottle. 
• Deep Water Culture (DWC) (low to medium cost; good for small to medium-scale setups, and plants like lettuce, herbs, and leafy greens):  I looked at the GardenCube and AeroGarden (which will hook up via wifi to Alexa.) Plants are suspended in a nutrient solution with their roots submerged in water. Air stones or pumps oxygenate the water, like in an aquarium. 
• Kratky Method (low cost; ideal for beginners and small spaces): This is more of an ala carte method that you can assemble to grow in a bucket. This is a variation of DWC, but without pumps. The plant roots are partially submerged, and the water level gradually drops as the plants take up nutrients. 
• Ebb and Flow (medium cost; good for growers with a little experience): Plants are in a medium (like clay pellets), and a pump floods the tray with nutrient solution periodically before it drains back to the reservoir. Most of the ones I looked at were fairly cheap, but probably best for an outdoor situation. Once you’ve seen one in action you can probably build one on your own. 
• Nutrient Film Technique (NFT) (medium to high cost; good for leafy greens and herbs): A continuous flow of nutrient solution runs over the roots in a shallow channel, providing constant nutrition. Requires careful monitoring of solution flow and pH. More for the willing scientists in our group. 
• Aeroponics (higher cost, best for advanced growers or big setups): Roots are suspended in the air and misted with nutrient solution. This is a highly efficient system but seems to require more technical maintenance. 
• Vertical Setups, Towers, and Greenwalls (high cost, more for commercial scale): These systems involve growing plants in stacked vertical towers. They typically use NFT or aeroponics and are designed for high-density production in limited space. Probably not happening in your dining room. 
• Aquaponics (DIY to VERY EXPENSIVE): A system combining hydroponics and aquaculture (raising fish). The fish poop provides nutrients for the plants, and the plants filter the water for the fish.

Tips for Success in Indoor Hydroponic Gardening  

1. Choose a plug and play type of kit with all the ingredients included, especially if you’re a beginner. I suggest a simple DWC type with a reservoir and a bubbler. There are plenty of these available for less than $100, and so for fairly cheap you “get your feet wet,” kill some plants, work out the kinks, and learn a lot. Once you have some experience, branch out, expand, and try more challenging options.  
2. Pick easy plants. I recommend herbs and leafy greens for beginners. You can easily eat your failures and try again. Keeping stuff alive long enough to actually ripen fruit takes experience and a lot of luck. 
3. Take care of your water. Keep reservoirs dark to prevent algae growth. Use filtered or distilled water, or rainwater if you can get it. If you use tap water in Philadelphia, it usually comes with both chlorine AND chloramine. Letting it sit out for a day helps remove the chlorine, but setting it in the sun is better, as UV light helps evaporate out the chloramine. 
4. Maintain proper water and nutrient levels. Sometimes there’s an app for that. Other times you actually have to learn science and use pH tapes. Often kits will have lights and dials to warn you when water and nutrient levels need attention. The plants will also warn you, especially when water levels are too low! 
5. Keep it clean. Growing in water might help avoid soil-borne pests, but aphids, whiteflies, and mealybugs are contagious and happily move from other plants to the newcomers. 
6. Maintain an air flow. Small quarters set the stage for mildew. Run a fan if you need to keep humidity down between plants. And again, keep surfaces around your setup clean. 
7. Don’t be afraid to DIY it! ‘Nuff said. 
8. Talk to other gardeners. Trade ideas. Touch things. Read a lot. Take a class. Join a garden club in person or online. 
9. Don’t give up your outdoor garden. You still need to touch dirt!  

Lessons Learned and Decisions I Made Along the Way 

• I analyzed my space and decided to NOT use the windowsill. It’s too cold at night, and the cats complained. 
•  If the grow lights are going to be on 14-16 hours a day, this machine needs to operate where it’s not going to keep people awake. 
• I chose a GardenCube because it seemed like a good learner model, it was cheap (under $50) and it seems replacement nutrient solutions and planting plugs will be easily available. It’s fairly straightforward, and it’s easy to see all the parts if I need to. I should be able to start seeds in it for my outdoor garden, or root cuttings from other plants. I’m not yet ready to run things from an app. 
• I’m going to explore the option of a garden tower when I get better at this, to see if it will work outdoors, or even in a classroom. 
• I’m still not giving up my outdoor garden.