A new reader (a container gardener) writes and asks, “Could you give me some advice, and could you do a blog about the unique issues with container gardening?”
Some Folks are Unable to Garden in the Soil
One possible situation for some gardeners might be to either garden in a container or not garden at all. If that’s the situation the gardener deserves a lot of credit for taking steps to grow in containers in spite of the difficulties it can pose. (Not to mention all the extra tending it takes.)
I don’t garden in containers, although I’ve used grow bags. I’m an in-soil organic gardener who looks to nature for inputs rather than buying packaged products. Answers given here will most likely be very different than if my reader and her husband had asked someone who is a conventional container gardener.
Help to Better Determine How to Proceed
I can’t tell Melissa what to do or what her exact problem is. But I can point out certain things that she and her husband might consider to better determine how they should proceed.
No “Silver Bullet” Answers/ Just Solid Principles
Gardeners looking for what I call “silver bullet” answers, may not find my answers suitable. For example: add a little of this and a little of that; use this or that potting mix and add such and such and it’ll fix everything.
Over 10 years of writing for TendingMyGarden.com, I’ve posted almost 800 articles. A great percentage of those posts deal with PRINCIPLES that are the foundation to growing healthy, nutrient dense food.
(I’ll link to some of the these posts as we go along and/or list them at the end.)
Principles are fixed. Ways a gardener can apply principles are numerous. It might take some creative thinking and experimenting to apply them to container gardening, but it can be done.
Will/Can A Potting Mix Duplicate Soil Conditions?
A common mixture for potting soil contains one part peat moss, one part perlite or vermiculite , and one part compost. Almost all sources I’ve seen online recommend this combination or a similar one for containers.
Keep in mind that when you garden in containers there is no way to duplicate (with just peat, vermiculite or sand, a little compost, and/or some type of synthetic fertilizer) what takes place in the miracle of soil.
Real soil doesn’t come in bags. Real soil is made up of sand, clay, organic matter, water, air, minerals, and a multitude of living organisms. For more details on the differences in real soil and fake soil see this post.
As I explain in many posts, your best growing beds will almost always be in your existing soil improved with organic matter.
By following natures example as closely as you can, you can increase your chances for bountiful production and more nutrients from all you grow even in containers.
Know What’s in Your Potting Mix and Why It’s There
Whatever mix you decide on for your containers, know what’s in it and why it’s there. This will go a long way toward helping you determine the cause of a problem should you have one.
Unfortunately we all need to first consider Residual Herbicides.
If you make your own compost and are absolutely sure you know what went into it then you have nothing to worry about.
If you’re sourcing compost – whether produced on a small scale or a large scale – you need to consider residual herbicides.
Certain chemicals that are sprayed on crops or land don’t break down for years. The vegetative growth from that land or crops finds its way to compost facilities. When someone buys the compost and applies it, it can kill their plants.
Material can come from so many sources that companies (or municipalities) have no way of knowing if it contains residual herbicides. Thus, it ends up in the product they offer.
For more details about these herbicides see my post Residual Herbicides in Composts/Grow Mix/ Potting Mix/Manure. (An additional post is also listed at the end.)
The good news is there is a way to test products for residual herbicides. I’ve written how to do it in this post How to Test for the Presence of Herbicides.
Some Other Possible Ingredients in Potting Mix
Peat Moss (a/k/a Sphagnum Peat Moss)
This is almost always added to potting mixes because it holds as much as 20 times its weight in water. It’s said to also hold on to nutrients that a gardener adds.
Other than that, it adds nothing of value for plants. Nutrient content is microscopic if any.
It also creates problems to deal with. It’s pH is very low (in the area of 4.0 to 5.0). The compost that is added usually compensates for that.
Once saturated with water, it doesn’t drain well and has to be mixed with something like perlite to promote drainage.
One of the worst problem I’ve found is once it dries, it’s difficult at best to get it wet again. When you add water to a container with dried peat moss, the water only runs down the sides of the root mass. After that it drains out of the holes in pot, rather than being absorbed by the plant.
Made from real coconut fibers, coir is sometimes used instead of peat moss.
It’s my understanding that long and short fibers are used. If this is the case it should have good water-holding ability and good drainage without the addition of vermiculite.
Quality can vary greatly. It will change with the region and with sources used to make it.
If not Certified Organic it can contain conventional Mushroom casing mix and/or feed lot dairy manure. You’ve got a 50/50 chance that it will or will not container residual herbicides.
Bark (NOT wood chips, but bark) can made an excellent potting mix. Many big wholesale growers use it. They order bark by the truck load; either hardwood, pine, fir, hemlock, etc.
They might let a pile sit for 2 or 3 year and then mix it with a year old pile (making it 10% of the mix) to give them the best texture for drainage.
If it’s decomposed too much it holds too much water for a potting mix.
Another important attribute of bark is it’s porous. This allows oxygen to pass through so the roots can breathe.
Nurserymen may or may not add some compost to the mix or even some pea gravel (for drainage if necessary).
As the bark continues to decay it also adds nutrients.
Sand will eventually get into all the places in the mix that allow for oxygen to move to the roots. Once this happens and the roots can’t breathe the plant will die.
It’s purpose is to improve drainage.
It’s purpose is to absorb water and then gradually release it.
Wetting agents ( known carcinogenics)
Fertilizers (Keep in mind that artificial fertilizers can never duplicate nature in spite of what chemical companies want you to believe.)
Something to Think About
These additions to a mix to accomplish drainage, water retention, pH balance, and nutrients, is ALL accomplished in in-soil gardening with the simple addition of organic material to soil.
The Ingredient Missing in Many Gardens and Probably Almost All Containers
An important concept for all gardeners to understand is the value of organic residues in the soil.
You may be thinking — “But I add compost and that’s organic matter from organic residues.” And you’re right of course.
But it’s very likely that your bagged compost (and even homemade composts) are lacking diversity in their makeup. More than likely they won’t give you an adequate supply of the many needed nutrients that come from real soil. It’s not just finished compost that benefits soil and plants.
Consider Using Quality Grow Bags
Grow bags are as close as I’ve come to being a container gardener.
The grow bags I used were made from a two layer special fabric that’s breathable and allows good drainage.
In a pot or planter roots will circle. That hampers growth. In these grow bags roots grow to the edge and are then “air pruned”. When that happens the roots branch. And the root system is more extensive which makes for better plants.
A good grow bag releases up to 30 degrees more heat than a plastic pot. Thus, roots stay cooler and can grow in hotter temperatures. Any soil life inside the grow bag can stay alive and continue to “work” in the soil.
In one of her emails to me Melissa said, “We are having only partial success with our container garden in the hot summers here. ”
If in fact the hot summers are part of her problem a good grow bag might be worth a try.
It’s been so long since I bought mine that I don’t remember where I got them.
But Jim and Megan Gerritsen at Wood Praire Farm have these quality “Smart Bags” available for you online.
(Jim, by the way, is one of the leading potato growers in the country. And Megan of course works right along side of him. I’ve written about Jim here.)
What I Used to Fill My Grow Bags
I don’t think it possible to fill containers or grow bags with just soil and be successful.
You need organic material to not only feed the soil, but to help aerate the soil, create good drainage, and hold moisture. (Again, I encourage you to digest the post on Organic Residues.)
In combination with organic materials (decaying straw and/or leaves), I used soil that I shoveled from the bottom of a cold compost pile.
In another bag I used a pitchfork full of straw in the bottom and then added about an 80/20 mix of soil and leaves. The soil was dark with organic matter and loamy.
I mulched the top heavily to keep the organic material on top from oxidizing and to help hold moisture.
In a month, earthworm were in the bag in abundance.
If you prepare your bags in the fall and let the organic material decay over the winter you should get even better results. By doing this in the fall you could even add some grass clippings (dried so they won’t get slimy), kitchen scraps, and plant residues.
By spring much will have broken down to enrich the mixture and you can add more soil and dried organic materials. (Leaves are my favorite for mixing with soil. If you want to you can cut them with a lawn mower for a more consistent mix.)
For more information on how the grow bags performed for me, I’ve linked to two post on that topic at the end.
Up until the last six or so years drought in summer was the norm here. It usually lasted 4 to 8 weeks. Sometimes 12 weeks.
By using my 3 keys I don’t have to worry about not being able to water my garden. I do save two trashcans of rainwater for watering seedlings and transplants. If drought goes longer than 4 or 5 weeks I can selectively haul a watering can of rain water to a plant that “really” needs it.
Since the mix in my grow bags is basically the same as in my garden beds (soil with organic material), I don’t usually have to haul water to those either. As we all know if we’ve used any kind of containers, they’re not going to “hold” as much water for reserves as gardening in the soil.
If drought goes longer than 4 weeks I consider giving the “bag” a large watering can of water when it’s necessary.
Watering plants is so promoted and advertised as being what needs to done, that most gardeners have a hard time refraining from it even when they’ve been presented evidence that it’s not necessary in most cases.
Over watering can do more damage than under watering. And this is especially is true for container growing.
A rule of thumb for plants in containers is to water only once every 24 hours.
Even if plants wilt on a hot day, it doesn’t necessarily mean they need water. It could be that they can’t take up as much water as they need. They’ll start to recover as soon as the sun goes down. For details see my post One Reason Plants Wilt and Actions that Help.
For more details three posts on watering are linked to at the end.
More About the Reader’s Situation
A few years ago Melissa and husband moved to Delaware from a state further north.
She considered herself a successful container gardener before moving.
Now her cilantro, which she previously had in abundance, dies immediately; onions are rotting, garlic is drying out, and sweet potatoes don’t get any larger than thumb size.
All the other herbs and vegetables are okay. And she indicated that the same mix is in all the containers.
My general comments about the specific problems:
The Cilantro Might not be as Much to Worry about as the Other Problems.
Cilantro likes cool weather. When mine comes up in the spring I never know just what it will do because it depends on the weather. Once it warms, the Cilantro is done. So if it warms up early, I don’t get cilantro in abundance.
I don’t know that this is Melissa’s cause, but it could be.
Onions are Rotting
Melissa ordered transplants “from Dixondale Farms and followed their instructions.” She “watered them twice daily during the really hot days, and when the soil was dry on other days.”
I’ve grown onions for over 40 years and have NEVER had onions rot in the ground. (With the exception of a few that contracted either pink root or white rot that was introduced into my soil from purchased transplants a several years ago. And I don’t think that’s Melissa’s problem at all.)
The decade I grew for market I planted at least 2,500 onions each year. Since Bill’s been gone, I plant only 1,000 or 1,500.
If the soil is very dry when I transplant onions seedlings, I’ll water after I plant using a watering can. Other than that, I’ve NEVER watered onions. Not ever! And the only difference in a dry year and a moist year would be a slight difference in the size of the onions.
I’ve seen people be very successful growing onions in large containers, but they mimicked in-soil growing conditions.
Although I don’t know enough details about her situation to make a definite judgement there are a few obvious things that come to mind.
- Over watering
- The next obvious thing would be the potting mix although she indicated that other vegetables in the same mix are doing ok.
- A large tented gazebo covers half of the deck where the plants grow. I don’t know if the onions are placed in this area or not. If so, I would put them back in full sun.
Garlic is Drying Out
- Garlic is a cool weather crop. Although it’s possible to get results from spring plantings, the most success will come when it’s planted in the fall, mulched, overwintered, and is then ready for harvest by late June or July.
- The container should be large and able to accommodate cloves being planted 3 inches deep and about 4 to 6 inches apart. (6 inches is preferable.) And in full sun.
Sweet Potatoes are Thumb Size
I’d have to know a lot more details before even commenting on the sweet potatoes.
My Comments on Fertilizers Used
Reader says, “I fertilize with compost from Home Depot, Bill’s, and rock phosphate.
“I had never heard of rock phosphate, but it was recommended by a tomato website. I was previously having trouble with container tomatoes as well. When I googled it, I noticed it’s recommended for a lot of plants, which have responded pretty well to it.”
I recommend definitely testing the Home Depot compost for Residual Herbicides. (Until the exact cause of the problems becomes clear I would check even the Black Gold product for Residual Herbicides even though it might be just fine.)
(I’m not familar with Bill’s.) Test it as well.
Regarding Rock Phosphate
My guess is that the almighty dollar is responsible for rock phosphate being touted as an organic fertilizer. It’s a mined (rock) fertilizer and other mined fertilizers are not considered organic.
There are other reasons that even non-organic growers may be wasting their money with rock phosphate.
It contains limestone and clay as well as a high concentration of phosphorus (P). Most garden soils have plenty of phosphorus. Adding more can be detrimental as with any supplement.
I’ve read that it doesn’t mix with water to become available to plants unless the soil pH is below 5.5. But even with the peat moss in the potting mix you can be sure the producers have balanced the pH to be higher. Otherwise the plants would die.
There’s so much bad advice online. It seems we have to constantly ask ourselves – how much experience do these people have who are giving the advice? How are they funded? What are they selling? etc.
#1. Test for Residual Herbicides even if you feel certain that’s not the problem.
#2. Consider the information in this post (and all the others linked to) to help you get as close to the way nature does things as possible. There’s a lot here and it’ll take time to digest. Especially if you’re not familiar with working with nature and are not an organic gardener either.
#3. Cut watering down to once a day. You may have to wean yourself off the habit. Also you might have to make some adjustments to your mix depending on what you find. Save and use rain water especially on food plants. If you don’t have enough rain water, let buckets of municipal water sit for 4 or more hours so the chlorine will dissipate. (I’m not sure about the chloramine they’ve added in recent years.)
#4. No matter how tempting, don’t add any ammendments unless you know for a fact you need it.
If you’re a container gardener you may be pleasantly surprised to have even greater success by following as close to nature’s example as you can.
Suggested Reading Pertaining to Topics Discussed in This Post
Read this post for more information on Mushroom Compost: The Word Organic without the OMRI-seal Doesn’t Mean Much
If you’re wondering how in the world hydroponics became eligible for the label Certified Organic – you’ll find the answer in this post: Information to Think on Before you Purchase Hydroponics etc. Of course the nutshell-answer is it was all about money and lobbying by big business.
All content including photos is copyright by TendingMyGarden.com. All Rights Reserved.