Since the recent bucket score, I've been trying to gather some quick information about the difference between vegetables grown in containers and vegetables grown directly in the ground and what I could do to get the best yield and the healthiest plants possible in containers.
You know what I found? Not much.
Granted, I didn't spend hours and hours searching as I'm more of a learn-as-I-go gardener, but the information is pretty skimpy for someone who just wants to understand the basics instead of being smacked in the face by mounds of scientific data. I was frustrated - until I came upon a posting at GardenWeb that was exactly what I was after.
Someone asked if it was possible that they'd gotten smaller fruits (pumpkins and squash) because they'd used regular garden soil and manure instead of potting soil and fertilizer in their containers.
As I started reading the first response to that post, my jaw dropped lower and lower. What a great, useful, thought-provoking post!
I emailed and asked the original poster if I could repost his response here as it was full of things I thought others might also find useful, and to my great joy, he said yes.
So, without further rambling, here is the entire response originally posted by 'justaguy2'. Hope you enjoy. I sure did!
"Yes.
That in ground grown plants do better than container plants is a myth with some facts surrounding it.
Simply put growing a plant in the ground doesn't take much more than working up the soil, a little fertilizer, a little water and a little luck in terms of weather, pests and disease. Almost forgot about the sun, that is important too ;-)
In containers the plants are 100% dependent upon what we provide so if we fail to understand what they require or simply don't do it, they suffer as a result. Comparing container plants to in ground plants is like comparing fish in an aquarium to fish in a lake. Fish in an aquarium can do better than fish in a lake, but it takes a dedicated and knowledgeable aquarist to pull it off.
In containers you cannot get the maximum potential from a plant growing in compost,manure or soil. That is what is ideal for growing in the ground, not in containers.
Containers are a different world. As one poster (Rhizo) has said in the past (I am paraphrasing), the ground is a soil system. We can put soil in a container, but we won't have the soil system working for us.
To grow veggies just as lush, vigorous and healthy in a container as we can in the ground we need to understand the big 3.
Sunlight is key for both ground and container growing so I won't comment on it here.
The first of the big 3 is water. Most soils retain a lot of water. Read the instructions for most plants and they just say to provide an inch of water when it doesn't rain. An inch of water per week in containers=brown, dry, dead plants. May work in many soils in most climates, but not in containers. In containers plan on watering daily.
The second of the big 3 are nutrients. Soils with a clay content or those amended with organic matter have an ionic charge that holds onto nutrients. In a container the need to water frequently results in nutrients being flushed out quickly. They need to be replenished frequently or growth suffers.
The last of the big 3 is oxygen. This is the most overlooked of the critical ingredients to success in containers. Those of us with heavy clay soils understand how easily our soil compacts and the negative effect it has on our plants so we amend it, till it, fork it, aerate it etc. We do this so more oxygen can make it to the roots of our plants. We may not realize this is why we do these things, but this is the reason. In a container we have solid walls that don't allow oxygen through except from the top. In the ground we have a soil system that handles oxygenation, in a container we do not.
If you want to grow container plants that not only rival in ground plants, but exceed them, here is how you do it:
1. Water. If a plant is growing and transpiring it is losing water. This water must be replenished via the roots. If the roots can't access this water the plant stops growing, wilts, browns and dies. The first step is it stops growing. If we don't keep up with watering we lose growth even if we do not see wilting or browning. We need to make certain our plants never lack water. How do we do this?
If you can water daily without fail this isn't an issue. If you can't then use self watering containers such as EarthBoxes and similar to extend the watering interval and if this isn't enough add an automated watering system. Bottom line is plants that lack water, even temporarily, will underperform those with a consistent supply of water.
A large tomato plant when producing fruit can use 2 gallons of water each day. Think about that for a minute. 2 gallons of water each day and many grow tomatos in 5 gallon buckets and the latest fad is growing them upside down in containers even smaller. To perform optimally a large tomato plant in such a container needs to be watered at least daily and probably 2x daily and maybe more often in arid or windy climates. The solution is a larger container or an automated watering system.
2. Fertilize heavily and often. Most veggies need a lot of water and a lot of nutrients. The frequent waterings containers require result in nutrients getting flushed out quickly. In the soil a watering just means nutrients get pushed an inch or so lower in the soil column. In a container they are gone. This means fertilizing in a container a couple times during the season just won't cut it. A highly available form of nutrients should be supplied at least once every 2 weeks and more often for the nutrient pigs (most veggies).
Additionally a controlled release fertilizer like Osmocote or similar should be mixed into the planting mix. Let's not forget about the micro nutrients such as calcium, magnesium, sulfur, iron or any other nutrient. In most soils the minor nutrients are present in adequate amounts and simply adding organic matter ensures they remain that way, but containers are different.
Either use a fertilizer that supplies all nutrients or plants will not perform up to par. They are called 'essential' nutrients because they are essential. Most soils have them and no container mixes do. We must supply them for best results. There are some synthetic fertilizers that are complete and most organic fertilizers (liquids) are. One of the best is Neptune Harvest hydrolyzed fish fertilizer. The competition pumpkin growers swear by it. It's not all that special, it is just a product that contains every plant nutrient in a reasonable ratio. A plant lacking any nutrient major or minor has a growth interruption or worse, it grows poorly and then needs to repair the damage. In most soils this is an infrequent problem, but in containers much more common for those who feed nothing more than N-P-K or Miracle Grow (which does have some, but not all, of the minors). All plants require *all* essential nutrients major and minor without exception.
3. The last of the big 3 is the most misunderstood. Oxygen. As long as our garden soil is reasonably decent in terms of tilth we don't have to worry about it. In containers we do. Carbon dioxide is an essential plant nutrient as is oxygen. We don't normally think about CO2 when growing plants, but I assure you those folks growing pot as a cash crop indoors do. They understand it so well they buy CO2 generators just for the extra yield. I also assure you those growing plants in a planted aquarium understand the need for CO2 as well. They buy CO2 injectors. For those of us growing out doors and out of water, we just don't think about CO2 as there is enough in the air. We take it for granted. We do this because we can.
With oxygen we can take it for granted when growing in soil (unless it is severely compacted). When growing in containers we cannot take it for granted. Oxygen is to container plants what CO2 is to aquarium plants and the drug dealer's pot plants growing in his closet. Both groups spend hundreds of dollars on high tech grow equipment to give their plants what they need. And that is CO2, a greenhouse gas.
Most of our containers are impermeable, they do not allow gas exchange except through the top. The sides and bottom do not allow any gas exchange.
Here is an easy experiment you can perform at home to understand how oxygen (a plant macro nutrient we take for granted) gets into containers: Take a drinking straw and place it in a cup of water. Place your finger over the top end of the straw and remove the straw from the water. Notice that the water remains in the straw in defiance of gravity as long as your finger is over the top end of the straw. Release your finger. The water runs out freely.
What just happened?
Water cannot run through our containers and out the drainage hole without also sucking in the air as it goes. Watering a container is what replenishes the oxygen in it. In a soil, watering too much displaces oxygen, in a container it replenishes it. The water itself doesn't have enough oxygen to sustain plants for long though. This is why a coarse mix rather than a mix of small particles is best. A mix of soil, compost and manure is very small particled. Sure, a watering will suck the air into the mix, but where will the oxygen get stored in the mix with all those tiny particles pressed against each other? This is why we need a mix of larger particle sizes. To hold the oxygen we introduce with each watering.
To summarize:
We need to water often. Water brings oxygen, but flushes nutrients.
We need to fertilize often. We do this because the frequent waterings flush nutrients out of the container.
We need a porous mix. We need this to hold the oxygen that our watering sucks in. The porous mix means more oxygen as well as the need to water more often. It is a double edged sword.
Master these 3 things and you will never again believe in ground plants out perform container plants.
Get a disease in your soil and you are stuck with it. Get a disease in your container, dump the mix, rinse with bleach water and no more disease. Put a plant in the ground and find out the location is bad for it and you are stuck. In a container, just relocate it.
Have a major storm bearing down on your location? Take your containers into your home, basement, garage or shed and all is well. If the plants are in the ground, you best pray real hard.
I could go on, but won't. There are advantages and disadvantages to any method of growing, but container grown plants including veggies can certainly out perform in ground plants if the container gardener understands the big 3. "
