Do these five things properly and you’ll get a good harvest.
There are only five variables that you have to worry about to be a success at container vegetable gardening. And isn’t it nice that it’s this easy? 🙂
#1 Pot size
This is one place where bigger is better.
A tomato can easily reach 6 to 8 feet tall in a single growing season and produce 100 pounds of fruit. This means it requires a significant root space and water reservoir in the soil.
The minimum amount of soil that you can realistically use is 6 to 8 shovels full of soil. (plan on more) This minimum will require a daily watering most of the season, and twice a day watering in the heat of the season. I’ve done this in a green garbage bag but it wasn’t easy.
This means bigger is better (at least in this one example) 😉
Stressing a plant such as a tomato with a slight lack of water will create disease conditions such as blossom-end-rot.
Small pots lead to watering problems which lead to this major fruiting problem. In this case, it’s a physiological disease as a result of a lack of calcium being moved to the fruit and some people think that adding calcium to the soil is the solution. The vast majority of soils do not require extra calcium, but the plant does require water to move the calcium up to the fruit.
So a lack of water will create problems in the harvest. You can read more about these black spots on the bottoms of your tomatoes here
Another variable with pot size is soil temperature. Smaller pots have higher soil temperatures then larger containers and the swing between high and low temperatures is also greater
This swing in soil temperature will also reduce harvests. When the soil temperatures get too high, plant growth will slow down or stop.
Note that stressed vegetables such as lettuce will taste bitter.
Note that small, black, plastic pots are the worst because not only is there a reduced soil amount, the black plastic also warms up enough to kill tender roots if left out in the full, hot summer sun.
#2 Get the Container Soil Right
Container gardening requires a different kind of soil then normally found in garden soil. The bottom line is you want a soilless mix with a peat moss base rather than any kind of garden or potting soil.
The mechanical forces on the soil in a container are much greater than the mechanical forces in regular garden soil
For example, when you water a container you are applying significant depths of water and pounding the soil in such a way that it will not be replicated in normal garden soil unless there was a flood
Think about it for a minute, in a container you apply 1 inch of water in the space of 1 to 2 min
Imagine what would happen if 1 inch of water came down as rain in only a minute or two. (You *really* don’t want to be out there in that storm!) 🙂
For this reason, we use peat-based soils such as Pro-mix that are designed to withstand this kind of watering pressure.
Do not add regular garden soil to any container. And read the label on the bag — if it says “garden soil” or “topsoil” do not use it in a container.
#3 Watering Properly — A Simple System
The rules of thumb for watering any container apply equally to vegetable container gardening.
Use your finger.
- Put it on the soil and if it comes away dry, water heavily and thoroughly so that water pours out the bottom of the pot.
- If your finger comes away damp, do not water at this time.
- If you do this in the morning, check again 8–10 hours later in the shoulder seasons (spring and fall) and 4–6 hours later during the height of the summer.
Early in the season, you may find that watering is not a daily chore but later in the heat of the season when the vegetables are growing strongly, you may indeed find that twice-at-day watering is necessary.
This is why really large pots have an advantage over the smaller ones — more even availability of water.
#4 Feeding For Growth and Flowers
Doug’s first rule of gardening states, “You only have to feed your plants if you want leaves, flowers, or fruit.”
This is pretty simple gardening, you feed if you want to see good growth and good harvests.
This is not an option.
I’ve had a lot of gardeners tell me they don’t feed because their soil is “good”. (Doug goes speechless when this happens)
In a container, I try to feed at least once a week during the height of the harvest season to keep the plant growing and producing well.
A weekly feeding earlier in the season is fine. In our greenhouses when we were growing commercial tomatoes, I used to feed every time I watered (daily) with a weak solution of fertilizer so the plants were never nutrition-starved.
I normally recommend fish-emulsion because I’ve had great results with it. But any organic liquid-based fertilizer is fine.
#5 What plants can I grow?
I really do not understand the confusion about growing plants in a container. If you follow the four major rules above with regard to pot size soil, watering and feeding there’s absolutely no plant that will not grow successfully in a container.
- It’s far easier to ask, “What plants can’t you grow?”
- If you can grow it, you can grow it in a container.
Mind you, there’s always somebody trying to sell you some new gizmo or technique to “help” you.
But no gizmo can possibly substitute for the 4 gardening techniques above.
This isn’t rocket science, it’s simple gardening. If you get your watering done properly, and feed your plants every week, then you’ll be surprised at just how easy this kind of container vegetable gardening is