Q: I’ve tried every kind of flower in my containers, but none bloom the way they should. The pots all get a tremendous amount of sun; I water regularly and feed them once a month. But the blooms are sparse and sporadic. What might I do to get the plants to flower more prolifically? — Erica Graves, South Bend, Ind.
A: It’s hard to comprehend how much fertilizer flowers in containers require. The main reason is all the water you have to give them, which quickly washes available nutrients out of the potting soil. Thus, a once-a-month fertilization schedule produces feast, then famine. Plants do best with a steady supply of a small amount of fertilizer, so feeding weekly is much better, or even twice a week at half the recommended rate (or a little less). Many commercial growers feed plants in pots with every watering, but that’s tough to do at home. A better way is to use time-release fertilizer granules, such as Osmocote. I often see these fertilizer granules sprinkled on the surface of containers, but that’s not the best way to use this stuff. The granules release fertilizer only when moist, and on the surface they dry out. It’s best to mix the granules right into the potting mix when you first plant the containers in the spring. Fill the bottom half of the containers with straight potting mix, because the fertilizer will inevitably wash downward. Only the top half gets a combination of fertilizer granules plus potting mix. Unless you’re filling a very large pot, it is easier to make enough for several containers at once. You might want to use a wheelbarrow and a hoe to stir the mix. Since most granular-fertilizer directions are based on the diameter of the top of the container rather than the volume of soil, mixing a big batch can be slightly tricky. As a starting point, use a 10-inch pot, which requires one tablespoon of granules and holds about 3 gallons of potting mix. Multiply by the number of pots, large and small, you have. Granular fertilizers normally provide continuous feeding for about four months. But if flower production should start to flag, supplement with weekly feedings of very dilute liquid fertilizer, a quarter strength or less. This will usually jump-start the flower show within a week.