Can I grow my tomatoes in pots? I get this question a lot, primarily from people who have limited growing space. But growing tomatoes in pots has many other advantages besides space saving, including the ability to overcome issues with soil, pests, location and light. Growing in pots gives you a level of control that is not always achievable when growing directly in the garden. If you pay attention to a couple of key differences between the two, you can successfully grow any variety of tomato in pots.
Choose the Right Pot
Operate under the assumption that no pot is big enough and find the largest container available for your budget. Tomatoes love to spread their roots wide and deep. In fact, I’ve seen tomato roots grow right through the holes in the bottom of their pot and into the ground below. The absolute minimum size is five gallons, but for me this is still too small. I go for the 20-gallon size or larger and I only do one plant per pot (although you can get away with two). Pots that are 20 inches in diameter and 18-20 inches tall are perfect. Stick with plastic as opposed to terra cotta or other materials. Plastic is inexpensive, lasts a long time, holds in moisture and minimizes heat build-up. Your best bets for finding big, plastic pots are Home Depot or Lowe’s. These tubs from Wall Mart work well, too, but you will need to drill drainage holes in the bottom. Wooden whiskey barrels are also great.
Find a Good Location
The best possible location for your tomato pots is somewhere that gets morning sun and then afternoon shade. If you need to move your pots around to achieve this effect, get planter caddies. Move them from sun to shade in the afternoon. The shade keeps the pots from overheating and negatively impacting the tomato roots. It also protects the plants themselves from the intense late afternoon summer sun, which can cause a number of problems for your plants, including reduced vigor and poor fruit set.
Use the Appropriate Growing Mix
It is very important to fill your pots with a good quality potting mix (also called potting soil). Go for the best potting mix you can afford. Most potting mixes are a combination of peat, vermiculite perlite, composted bark, a wetting agent and a fertilizer charge. Organic mixes often include worm castings. None of the mixes include earthen soil, which can contain pathogens that could become problematic in pots; so avoid using soil from your yard. I prefer to add some bagged compost to my mix (about one third of the total) as well as a slow release granular fertilizer. You can make your own slow-release fertilizer by mixing in the following ingredients for each 20-gallon pot:
- One cup blood meal
- 2 cups bone meal
- 1 cup kelp meal
- 2 cups greensand
- ½ cup of trace minerals like Planters II.
Plant Healthy Tomato Starts at the Right Time
It is critical to begin with healthy tomato plant starts. Look for plants that are between six and eight inches tall with thick stems and a green, leafy canopy. Plant starts grown in deeper as opposed to wider pots tend to have better developed roots, which are important for plant establishment after transplanting into your large pots. For our plant sale, we use a three-and-a-half-inch pot that is five inches deep like this one:
If your plants have not been acclimated to the outside, then it is important that you harden them off before you put them outside permanently. This process involves putting the plants outside in sunlight each day, starting with an hour and gradually increasing the exposure time by one hour each day over a week. This gradual acclimation helps the plants get used to direct sun, wind and temperature changes. When planting in pots you can take advantage of an earlier start because you can easily protect your plants from the elements (see Step 5 below). Nevertheless, it’s best to wait until the nighttime low temperatures are approaching 50˚F consistently before transplanting your tomatoes outside. When you are ready to plant, pinch off the first one or two sets of leaves at the stem and plant deeply, up to the next set of leaves. The parts of the stem below the soil line will sprout lateral roots, encouraging a stronger overall root system as the plant matures.
Provide Support and Protection
Even though you are planting in pots, you still need to support your tomatoes. I recommend putting a tomato cage either around the outside of your pots or insert the prong ends of the cage right into the pot. The best material for do-it-yourself tomato cages is concrete reinforcement mesh, which you can buy in rolls at home improvement stores. To make a cage that is 24” in diameter and five feet tall, you will need to roll out about 7.5 feet of wire mesh. This size cage will fit around your pot and provides a structure to hold up the tomato plant and to support a protective covering to hold in warmth, block wind, keep out insects and shade your plants. I like to wrap my cages with a sheet of plastic early in the season to provide protection as the plants establish themselves. This will keep some heat in and keep out marauding beet leaf hoppers, which spread the fatal curly top virus. Later as the weather warms up, you can switch to row cover material using the cage as a frame.
Set Up Your Watering and Mulch
Growing tomatoes in pots requires that you pay much closer attention to watering. Pots can dry out quickly on hot days and plants sometimes need to be watered every day. The ideal watering setup is drip irrigation on a timer. This strategy allows you to water evenly and consistently without having to think too much about it. Also, when you are away during the summer for extended periods, drip irrigation on a timer eliminates the hassle of having to find someone to water your plants. It’s fine to water by hand, but keep in mind that tomatoes in pots tend to dry out faster than those grown directly in the garden.
Another critical part your watering strategy is to mulch your pots once the tomatoes are planted. It is important to cover the soil to keep the roots cooler and the soil more evenly moist. You can mulch with three to four inches of just about any type of organic material. You can mulch with finished compost, straw, hay, pine needles, newspaper, cardboard, or dried grass clippings that have not been treated with herbicide. To make a finer mulch run over your organic material with your lawn mower to shred it into smaller pieces.
Tomatoes are heavy feeders, and supplemental fertilizer is especially important if you are growing in pots. If you added fertilizer to your potting mix at planting time, you should not need to fertilize again until your plants start to flower. When the first flush of flowering occurs, pull back your mulch and scratch another dose of granular fertilizer into the soil surface and add water to help the fertilizer penetrate the growing mix. At this stage, you want to be sure to choose a fertilizer that is high in phosphorous and not too high in nitrogen. High nitrogen fertilizers will result in a lot of leafy green foliage, but few if any flowers and fruit. The three letters for fertilizer are N-P-K, for nitrogen, phosphorous and potassium, respectively. Look at the numbers corresponding to these three ingredients on the fertilizer bag. The second number should be higher than the first. I also like to supplement with a foliar fertilizer from a sprayer. Organic fish fertilizer works well and gives the plants a low dose of added nutrients on a regular basis. I spray every two to three weeks early in the morning and coat the top and bottom of the leaves.