If everything on your balcony died by July, start with a bigger pot
Almost every container failure comes down to too little root volume, the wrong growing medium, or nobody feeding it after week six. All three are fixable at planting time.
A pot is a small closed system with no groundwater under it, no surrounding soil to wick from, and sun hitting it from the sides as well as the top. Everything that makes container growing convenient also makes it unforgiving.
The good news is that the failures are boringly consistent. Pots that die in midsummer are almost always too small, filled with the wrong thing, or unfed since the day they were planted. None of that is a skill problem, and all of it is decided in the twenty minutes when you set the pot up.
Size is doing most of the work
Volume grows much faster than the number on the pot suggests. Step up from an eight-inch pot to a twelve-inch pot and you have not gained half again as much room, you have roughly tripled it, because the width and the depth both increase. That extra volume buys two things at once: room for roots, and a reservoir of moisture that buffers a hot day instead of running out by lunchtime. A small pot in full sun in July can go from watered to wilting inside eight hours, and there is no technique that fixes it.
| Salad leaves, radishes, basil | 6 to 8 inches deep. Wide matters more than deep |
|---|---|
| Bush beans, chard, compact herbs | 3 gallons or so, and they will still want daily water in heat |
| Peppers, eggplant, determinate tomatoes | 5 gallons is the floor. Fruit set drops sharply below it |
| Indeterminate tomatoes | 10 gallons and up, or you will be watering twice a day |
| A shrub or small tree | At least a couple of inches of mix all around the root ball, in something heavy enough not to blow over |
Drainage holes yes, gravel no
Holes are non-negotiable, and a decorative pot without them is a cachepot, meaning you grow the plant in a plastic liner that lifts out. Cover the hole with a scrap of window screen or a curved piece of broken crock so the mix does not wash through, and stand the pot on feet or a couple of tiles. A drainage hole sitting flat on a paving slab seals itself against the stone within a season.
What does not help is the layer of gravel at the bottom that everybody was taught to add. Water does not move readily from a fine material into a coarse one until the fine material is saturated, so the mix immediately above the gravel has to become waterlogged before anything drains at all. The saturated zone that forms in the base of any pot does not disappear, it just moves up by the depth of the gravel, and you have swapped usable root space for a wetter root zone. Fill the pot with growing medium, all the way down.
Potting mix is not soil, and it expires
Garden soil in a container compacts into a dense, airless block within weeks. It behaves entirely differently once it is cut off from the soil around it, and the structure that holds it open in the ground does not survive repeated watering in a pot. Potting mixes are built for the job: peat or coir for water retention, bark or perlite or coarse sand for the air spaces roots need, in proportions that stay open when saturated.
What they are not is fertile. Most bagged mixes carry a starter charge of nutrients that runs out somewhere between four and eight weeks, and every watering flushes a little more out of the bottom. After that, whatever you feed is all the plant gets. Either mix a controlled-release granular feed into the medium at planting and forget it, or start liquid feeding weekly once the plants are growing hard. Use a high-potassium feed, sold as tomato feed, for anything you want to flower or fruit, and something more nitrogen-heavy for leafy crops and foliage plants.
Watering pots is its own skill
Water until it runs freely out of the bottom, then stop. A splash on the surface wets the top inch and leaves the root ball dry underneath, which is how plants die in pots that get watered every single day. The best moisture meter you own is your hands: lift the pot after watering and lift it again two days later, and the difference in weight is unmistakable within a week of paying attention.
If water pours straight out the moment you pour it in, the mix has not absorbed anything. Peat-based media are stubbornly water-repellent once they dry out completely, and they shrink away from the sides of the pot so the water runs down the gap and out. The fix is to stand the whole pot in a bucket or a tray of water for twenty or thirty minutes until the surface darkens and the pot feels heavy again. Then start watering properly before it gets that far next time.
What the pot is made of changes the routine
- Terracotta breathes, which cools the root ball by evaporation and dries it out fastest. Lovely for herbs and lavender, punishing for anything thirsty.
- Glazed ceramic and plastic hold moisture far longer. Plastic is the sensible choice for vegetables and for anywhere you cannot water daily.
- Metal in full sun cooks. Dark colors of any material absorb heat, and root temperature in a black pot against a sunny wall can climb well past anything roots enjoy.
- Fabric pots drain and aerate beautifully and dry out correspondingly fast. Size up if you use them.
- Group pots together in high summer. They shade each other's sides and the cluster loses moisture more slowly than the same pots spread out.
Winter is harder on pots than on beds
In the ground, roots sit under an insulating blanket of soil. In a pot they are exposed on every side and the whole root ball can freeze solid, which it never would in a bed. Roots are also less cold-tolerant than the top growth of the same plant, so a shrub that shrugs off winter in your borders can die in a container through identical weather. The rule of thumb is to treat a permanently potted plant as needing to be hardy about two zones colder than the zone you garden in. Move pots against a house wall, group them, wrap the sides rather than the plant, and empty terracotta before freeze-thaw splits it.
Anything perennial needs repotting every two or three years, and the signs are obvious once you know them: roots spiralling out of the drainage holes, water sitting on the surface, a plant that dries out faster every year. Slide it out, cut through the roots circling the outside of the ball with a knife, and either move up one pot size or trim the roots back and return it to the same pot with fresh mix. For anything too heavy to lift, scrape off the top two inches each spring and replace it with fresh medium and a handful of slow-release feed. That alone keeps a large pot going for years.