Keeping container plants happy

Petunias, grasses and fan flower, living in harmony. — Proven Winners

There’s no deck, no terrace, no patio or porch that doesn’t benefit from a dressing up with bright summer annuals in handsome pots.

Even if you haven’t the time or inclination to create your own living accents, any garden center worth its salt will tempt you with glorious hanging baskets and overflowing containers, pre-planted and ready to go. Unfortunately, you may find that a few weeks after you forked over the cash (sometimes, quite a lot of cash), your container plants seem to be failing in spite of the fact you’ve watered them faithfully.

When the flower-power gradually wanes to a paltry few blossoms and the foliage fades to a pale shadow of its former deep green, when the whole formerly beautiful thing appears headed for a premature demise, what’s gone wrong?

It could be you’ve failed to understand the single-mindedness of annual plants, which hurry to squeeze a full life cycle into a single summer. It also could be that you’ve been starving your plants and the poor little things are just too hungry to get on with the business of producing flowers. Arm yourselves, gardeners, with a pair of pruning shears and a package of general purpose fertilizer, and we’ll reveal the secrets of keeping those container plants happy.

Annuals include those familiar flowers of summer — petunias, marigolds, geraniums, nasturtiums — that mature and flower in warmth, die with frost and do not return the following spring (or ever). They are perfect container subjects because they can be induced to bloom all through the warm-weather months, unlike perennials, which generally don’t flower for much longer than three weeks no matter what you do.

There is a caveat here (I knew you could hear the “but” coming) and it involves preventing your annuals from setting seed. The successful act of reproduction convinces your plant it has completed its mission in life, leaving it free to leave this mortal coil. It will, too.

You can thwart this syndrome by removing spent flowers before they can evolve into seed pods. Snip or pinch off not just the petals, but the structure just below the blossom, where incipient seeds lie. Cut that wilted flower back neatly to the next set of leaves, and you’ll be doing the really right thing. The plant, deprived of signals that the next generation is on the way, will try once again to make babies, producing a fresh flush of flowers.

The only time you are relieved of the need to clip dead flowers (deadheading it’s called, with or without Jerry Garcia) is when the plant is sterile as are some hybrids like Wave petunias, or the plant automatically sheds spent flowers, as in the case of impatiens. Otherwise, get out there every few days and do the right thing.

Container plants get hungry. Feed them! — Proven Winners

If you can’t remember when you last fertilized your poor little plants, it’s been too long. Container-grown plants can’t send their roots in search of moisture and nutrients the way plants in the soil can and do. Pot-bound, your container specimens depend on you to keep the moisture coming, but every time you water, you are flushing nutrients away. To maintain plants at their peak, you need to consistently add fertilizer.

Experts recommend a two-step program for most potted annuals: Plant them in a potting medium that includes a slow release fertilizer, and dose them weekly with a general-purpose liquid plant food.

The slow-release pellets, offer the same kind of nutritional insurance that taking a daily vitamin does — it supplements a regular diet, supplying a broad spectrum of nutrients. If the potting soil you use doesn’t include this boost, you can mix in the recommended amount of such products as Osmocote.

Don’t think of potting up plants in ordinary garden soil, by the way. Repeated watering will compact it to the point where roots will struggle, and soil micro-organisms that inevitably hitch a ride may include harmful pathogens or critters.

Slow-release fertilizers are affected by factors like soil temperature, and are not sufficient by themselves. You still need to fertilize weekly with a soluble fertilizer with a formula of 15-30-15 or the commercial grower’s version specific to container plants, 20-10-20. You can alternates every two or three weeks with a “bloom booster” formula high in phosphorus — 10-52-10, for instance. This stimulates the production of new flowers.

When you fertilize, follow the dilution instructions on the package. And don’t just spritz the foliage, waving your hose-end sprayer around. Thoroughly wet the foliage and drench the soil. It is the roots, after all, that are primarily responsible for conveying water and nutrients to the plant’s top growth.

Feed those little puppies and keep their spent flowers clipped, and you’ll get the best return on your potted plant investment. If the plants have become irredeemably straggly before you begin such a regimen, cut the whole plant back sharply, fertilize regularly and you should see a rebound in about two weeks.

Remember, these are you most dependent plant children. Everything they need, they have to get from you.