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Help Your Container Garden Survive Your Vacation

   You’re about to go off on your summer vacation. You’ve stopped the paper delivery. Had the mail held at the post office. Turned off the air-conditioning. And arranged for Fido and Fluffy to be boarded at the local kennels.
    But what about your plants?
    Container gardens are particularly vulnerable in summer heat waves, so if you are planning to be away for more than a couple of days, you should make plans for your plants as well as your pets – especially if your garden is a collection of window boxes and sidewalk pots in the heart of the city, says Toni Ann Flanigan, a horticulturist who frequently gives talks on urban gardening for the Pennsylvania Horticultural Society.
    Sidewalk gardens create inviting oases that soften the hard edges of a city street. But plants in window boxes and terracotta pots – which are likely to be toasted by heat reflected off buildings and sidewalks – need to be watered every day at the height of summer, or maybe every other day for seedums, grasses, and other drought-tolerant plants.
    That’s not necessarily true for container gardens in urban or suburban backyards.

Dan Benarcik
Dan Benarcik, a horticulturist at Chanticleer pleasure garden in Wayne

Survival tips for containers
    “Everything is based on moisture retention,” says Dan Benarcik, a horticulturist at Chanticleer pleasure garden in Wayne who also lectures on container gardening to groups all over the Delaware Valley. You could probably get by without watering for a week or so, he says, by following a few simple suggestions.
    “If you can move smaller or medium-size containers into a shady situation, the shade relieves some of the moisture requirement. If you have the ability to cut the plants back – things like coleus or plectranthus, for instance – that, too, removes some of the moisture requirement,” Benarcik says. “And if you employ plastic saucers [under the pots] for one- to two-week periods, that will work as a reservoir for the plants to draw on.”
    Make sure you remove the saucers promptly when you get home, he warns, or it could lead to rotting.
    I can vouch for that. Because much of my gardening is done long-distance – at our country cottage in the mountains of south-central Pennsylvania – I constantly face the vacation dilemma of leaving my plants unwatered, sometimes for 12 days at a time. Occasionally, I’ve forgotten about the saucers I’ve put under various pots to conserve water – until the plants keel over and I find the roots have turned to mush because the containers have been standing in two inches of rainwater for who-knows-how-long. Drainage, as Benarcik points out, is essential; excess moisture must be allowed to run off.

Getting off to a good start
    Even more important than what you do with the containers now, though, may be what you put in them at the beginning of the season.
    “The time to consider moisture retention is when you are planting, because it is what is happening under the plants” that counts, says Benarcik, who deals with about 80 containers ranging in size from small to colossal for the terraces around the Chanticleer mansion.
    “I fill the bottom half of the containers with good, rich, organic compost that we produce on site – the same kind of compost that many gardeners have, with sticks and stones and bugs and worms and weed seed. The other half I fill with a soil-less medium that has good air space that allows young plants to root in readily.”
    Not only does the compost provide micro-nutrients for the plants, but it holds moisture well, he says. “As the plants develop, the more vigorous roots then plunge into the compost – and at that point you are usually hitting the hottest part of the summer, when moisture delivery is even more critical. If you have that base of compost, you could go three to four times longer [between waterings] than a pot that is filled just with a soil-less medium.”
    Benarcik uses a slow-release fertilizer such as Osmocote in the top few inches of the planting mix, as well as a liquid fertilizer every two or three weeks during the growing season to make up for nutrients that leach out during regular watering.
    “Any balanced fertilizer, 10-10-10 or 20-20-20, will do,” he says. “The plants can’t tell the difference.”

Container garden with pots and window boxes.

What about water-retaining crystals?
    Although Benarcik opts not to use moisture-holding polymers in his containers, urban-gardener Flanigan favors premier potting mixes containing both slow-release fertilizer and the water-retaining crystals for window boxes, hanging baskets, and similar containers that are in high-stress situations.
    “I think the mixes that have the crystals already mixed in get the plants off to a good start,” says Flanigan, who, as owner of Philadelphia Garden Inc., specializes in designing and installing smaller gardens in the city. In addition, about a month after planting containers, she begins using a fertilizer such as Jack’s Classic Blossom Booster every other week, and alternates that with mild applications of SuperThrive, which is not a fertilizer but contains nutrients, vitamins and hormones. The SuperThrive, she feels, helps plants during stressful periods, such as transplanting or hot weather.
    I’ve never tried SuperThrive, but – in my constant battle to keep my hanging baskets and window boxes alive in the country while I’m living in the city – I routinely use water-retaining crystals such as Agrosoke mixed in with the soil (follow the directions carefully so you don’t end up with a gelatinous mess), and I’ve tried a variety of other aids such as rain mats at the root zone, drip cones, and self-watering containers. Most seem to work to some extent, although occasionally I’ve had the same result with self-watering containers that I’ve had with forgotten saucers – the plants rot.

More containers and window boxes.

Get yourself a watering buddy
    But for city-dwellers who are going on vacation, regular watering is still the number one concern for those sidewalk gardens. The good news is that if you live in a city townhouse or rowhouse, you probably know your neighbors. Make a deal with a gardening neighbor who’ll be away at a different time to watch out for each other’s plants.
    “The buddy system of watering probably works best,” says Flanigan, and if the whole garden is window boxes and sidewalk pots, “you can do it from the outside without any trouble.”
    Make sure the buddy you choose is someone who knows how to water, though – that means slowly soaking the roots, not sprinkling a bit of water over the top foliage.
    “Be sure you get the entire soil plug saturated,” Benarcik advises. Some of those soil-less potting mixes can shrink away from the pots’ sides as they dry out, which allows water to drain off rapidly before it has a chance to soak into the mix or to reach the plants’ roots.
    The type of container you choose can also affect how often you have to water.

Pick the right plant – and planter
    “Terra-cotta, which is widely available, is probably the worst, because it transpires so quickly,” says Benarcik. “A high-fired, or glazed, type of pottery is a much more effective water manager. Plastic and metal containers are also fine, in that they will manage moisture and don’t transpire, but they heat up and cool down very quickly, and – depending on the color – can actually burn the roots with increased temperatures.”
    Picking the right plants helps, too. There are lots of heat-loving plants that do well in really hot spots, says Flanigan, which makes them obvious choices for city containers. Try lantana, angelonia, pelargoniums, Mexican portulaca, sweet potato vines, gaura, and annual climbers such as black-eyed Susan or hyacinth bean vines.
    And when the vacation is over? Just like you, your plants might have to re-acclimate to their normal routine. Remove those plastic saucers and give them a mild dose of liquid fertilizer (if they haven’t been fertilized while you were gone). And if your containers have been snoozing in the shade, they should be gradually reintroduced to their sunny situation.
    Neglect that follow-up care, and you could jeopardize all the efforts you took to give your plants a happy vacation at home.