You CAN grow any tomato in a pot, if you do it right! Growing tomatoes in pots or containers is much more demanding than growing them directly in the ground. They rely on you for all of their needs. It took master tomato grower Cynthia Sandberg four years of trial and error before she perfected her technique. Here it is:
Size matters: We recommend a 20 gallon GeoPlanter pot. GeoPlanter pots are made of a durable fabric, rather than plastic or wood, that lets roots breathe. When roots reach the fabric edge in the pot, they are air pruned, rather than becoming root bound. This pruning of the root tips at the wall of the container forces branching of thousands of fibrous feeder roots throughout the plant container. GeoPlanter pots are also convenient because they are light weight and able to be folded for storage. A 20 gallon container will hold only one plant. Anything smaller will hamper the plant's ability to produce fruit and remain healthy. Love Apple Farms will have the 20 gallon GeoPlanter pot available for purchase at our Tomato Plant Sale in Scotts Valley. The 20 gallon size is 20" tall and 15" wide. If you are using something other than a GeoPlanter, it must hold 20 gallons of soil and it must have drainage holes. A half wine barrel will hold two plants. GeoPlanter also sells PVC-framed planters in various sizes:
If you are re-using a container, you should disinfect it first. We use a bleach solution of one part bleach to 10 parts water. A simple quick dunk or spray, followed by a rinse with fresh water, should do the trick.
Potting Soil: Do NOT use garden soil or home-made compost in your pots. Tomatoes are disease-prone and one of the benefits of growing in a pot is that they cannot pick up any soil- or compost-borne diseases if you use a sterile potting mix. We recommend Gardner & Bloome Organic Potting Soil. It's available at our retail greenhouse in Scotts Valley or from Mt. Feed & Farm Supply in Ben Lomond, CA. You can go very wrong with potting soil, so don't deviate from this instruction. We still want you to put in the container all our recommended additives, but first add four inches of soil on the bottom of the pot.
Fertilizers: Our perfect planting amendments for pots are: 2 big handfuls of Gardner & Bloome Fish Bone Meal, 2 big handfuls of Gardner & Bloome 4-6-3 dry organic Tomato, Vegetable & Herb fertilizer, three or four crushed chicken eggshells, one big handful of 100% pure worm castings (available at our Plant Sale), and two aspirin tablets.
Once the amendments have been added (no need to stir), add more potting soil and place your tomato plant in the container, backfilling with soil as you go, until you've put at least half the stem under the soil. Tomatoes like to be planted deep - they benefit from it. Continue filling around the plant until the soil is at the very top of the pot. There's no need to firm down, watering will do that for you.
Watering: Water them in well. We'll water then once, wait about 10 minutes, then water again, wait, then again. It takes a lot of water to completely saturate the potting soil. Even if you see water draining out of the holes, that doesn't necessarily mean the root ball is soaked.
After you water the new plantings three times their first day, you probably will not need to water again for at least a week and probably longer. Tomatoes do NOT like to be saturated all the time, and you can easily kill the tomato by overwatering it in a cool springtime.
As the weather really heats up and your plant is getting big, they need more water. You may end up watering once a day if your tomato plant is 6 or more feet tall and it is consistently over 80 degrees. When a tomato is grown in the ground, it never needs watering that often. But in a pot, it does indeed (once the plant gets big and the weather gets hot).
Staking: The tomato in the pot will still need staking. Our 7 foot tall custom-made tomato cages can be popped right over them. If you treat the plants right, they can and will get up and over that 7 foot cage. We have a tutorial for you on how to make these mondo cages, found here.
Supplemental fertilizing: Even with all the goodies in the pot, your plants will start to decline in health around week six or so if you don't start fertilizing them from the top down. We use worm casting tea, made out of pure organic worm castings. Mix a handful in a five gallon bucket of water and fertilize with two gallons of that at least once a week. If you can't get worm castings, then use a good all-purpose organic liquid fertilizer once a week. You'll need at least two gallons of the diluted-according-to-directions fertilizer per pot per week. Start the fertilizing regimen around week six to avoid the summer doldrums.
We love to spray the worm casting tea on the foliage (along with an aspirin tablet for disease suppression). But tomatoes in a pot need more fertilizing than that, hence pouring a fertilizer mix IN the pot as noted above.
Shading the pots: If you're growing in a black plastic pot, the tomatoes love soaking up the extra warmth in late spring and early summer when the temperatures are still mild. But you need to take extra care starting in mid-summer to protect the rootball from overheating from excess sun on the black plastic. No amount of watering will keep the rootball happy. This realization was the last piece of the puzzle when we were trying to figure out how to grow a really great tomato in a pot. Here is a photo of our tomatoes in pots, with their 7 foot tall cages on them, with shade cloth pinned to the south side:
You need only shade the lower part of the cage, but we still pin it about a foot above the top of the pot, all the way to the ground. Small binder clips work great for pinning. Shade cloths can be purchased, cut to your desired length, at good hardware stores or at Mt. Feed & Farm Supply in Ben Lomond.
Finishing up the season: As your tomato plant winds down in vigor in the fall, you can compost your plants and the soil, but you should not re-use the soil next year in the pot. Re-using potting soil inside a container is never a good idea, as viruses and other harmful diseases can infect your plants the following season.
You can find more information all about tomatoes on the World Tomato Society website.