Q & A with Bob Polomski 3

Extension Consumer Horticulturist, Clemson University

How do I know if my lawn needs aeration? —H.S., Fair Lawn, NJ

Answer: Aeration, or aerification, is a cultivation practice used to alleviate soil compaction. This compaction commonly occurs from intense use, such as heavy foot traffic, athletics, or the passage of wheeled vehicles. While sandy soils typically resist compaction, clay soils are prone to it. Indications of compacted soil are thin turf or bare areas, puddling or runoff after irrigation, and certain weeds, such as prostrate knotweed (Polygonum aviculare) and goose grass (Eleusine indica.)

Compaction is usually most severe in the upper few inches of soil. Compressing soil particles reduces the pore space between them and impedes the movement of air, water, and nutrients to the grass roots. As a result the root system of the turf becomes shallow and drought prone. The goal of aerating the lawn is to loosen the soil and increase the availability of water, nutrients, and oxygen. This not only stimulates root growth, but it also enhances the activity of thatch-decomposing organisms.

While a spading fork can be used to punch holes in a small lawn, a sod-coring tool does a better job because it actually removes a plug of soil rather than simply displacing it. The device looks like an upside-down U attached to a long handle. The legs of the U are hollow tubes one-half to three-quarters of an inch wide. As the tool is used, earthen plugs are deposited on the lawn surface.

Larger lawns are best aerated with a power-driven core aerator. These can be rented or operated by a hired contractor. The working parts of these machines are spoon-shaped tines or hollow tubes. As the tubes are driven into the lawn, cores of soil are removed from the ground and strewn across the lawn. These cores, while unsightly at first, soon break apart. The microorganisms they contain help to decompose thatch.

Whatever machine you use, plan to go over the lawn twice. Travel once in one direction, then again in a perpendicular direction for best results. Lawns composed of cool-season grasses, such as Kentucky bluegrass and fescue, are best aerated in late summer and early fall, when there is less danger of invasion by weedy annuals, such as crabgrass. There should be at least four weeks of good growing weather remaining, to help the plants recover. Warm-season lawns, on the other hand, should be aerated in the spring, a couple of weeks after the lawn has completely greened up.

This summer I’ve been growing bananas outdoors. They are now between six and eight feet in height, and I’m wondering how to keep them over the winter. -J.F., Middleton, KY

Answer: There are several ways to overwinter bananas in cold climates. If you have a greenhouse or sunny window, you can move the whole plant indoors and keep it growing as a houseplant. If you are digging up your plant from the garden, you can detach any suckers from the main rhizome and pot them up individually.

Another approach is to store your plant in forced dormancy. Wait until just before frost, then cut off all the leaf blades and move your plant to a dark, cool, frost-free location. Water only enough to keep the root ball from drying out. After the last freeze in your area, you can take the plants back outside. New leaves will emerge from the pseudostem.

Some bananas are hardy enough to be left in the ground all winter. Edible bananas that can tolerate temperatures below freezing include ‘Red Banana’, ‘Ice Cream’, ‘Manzano’, ‘Golden Rhino Horn’, and ‘Orinoco’. In some zones only the leaf blades will be killed; in others, the entire pseudostem will be killed to the ground. One of the most hardy is Musa basjoo, the Japanese fiber banana. Its fruit is inedible, but the species is root hardy to USDA Zone 6 and even colder. With heavy mulching even the pseudostems can survive northern winters.

Can you suggest any ornamental grasses that are native to the United States? -B.P., Bemidji, MN

Answer: There are many native grasses with ornamental features (colorful plumes and seedheads, fine-textured leaves, and fall and winter color). In Minnesota, you should consider planting big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), side-oats grama (Bouteloua curtipendula), blue grama (B. gracilis), or prairie dropseed (Sporobolus heterolepis). All will flourish in well-drained soils.

For moister or wet areas, you can choose such native grasses as Kalm’s bromegrass (Bromus kalmii), blue-joint grass (Calamagrostis canadensis), Bebb’s sedge (Carex bebbii), switchgrasses (Panicum virgatum), wool grass (Scirpus cyperinus), indian grass (Sorghastrum nutans), and prairie cord-grass (Spartina pectinata).

For stream banks, ditches, and flood-plains, try bottlebrush sedge (Carex co-mosa), tussock sedge (C. stricta), sweet grass (Hierochloe odorata), river bulrush (Scirpus fluviatilis), and dark green bulrush (Scirpus atrovirens).

Many of these are available as nursery-propagated plants. If you are unable to find a source, make plans to collect some seed this fall from plants near your home and start them indoors for planting outdoors next spring.

I have a viviparous water lily, ‘Panama Pacific’, that often has sprouts that start in the center of the leaf but never mature. What’s the secret of starting a new plant?—M.S., Smithville, TN

Answer: Several tropical lilies undergo viviparous reproduction. In addition to ‘Panama Pacific’, these include ‘August Koch’, ‘Charles Thomas’, ‘Daubeniana’, ‘Margaret Mary’, ‘Mrs. Martin E. Randig’, and ‘Pink Platter’. Vivipary is less common in hardy water lilies, but it has occurred with ‘Colonel A. J. Welch’, ‘Perry’s Viviparous Pink’, ‘Perry’s Red Star’, and ‘Perry’s Pink Delight’. ‘Cherokee’ produces viviparous plantlets from flowers and buds. Water snowflakes (Nymphoides cristata) and water poppies (Hydrocleys nymphoides) also produce viviparous offspring.

In viviparous reproduction, a young plant appears from a fuzzy swelling, called a vivip node, that occurs on the surface of the leaf pad at a point where the leaf blade attaches to the petiole. In some cases, vivips may mature and bloom while still attached to the parent pad, but typically growth and development of the plantlet is arrested until the parent leaf begins to decay. Then the plantlet rapidly increases in size. The leaves and roots enlarge, and, left to its own devices, the plantlet will settle to the bottom and root in the sediment.

To speed development of your plantlets, detach the leaf from the parent plant and allow it to float in the water. You can also remove the pad and place it in shallow water in an aquarium or small tub, securing it to the bottom with a rock. Maintain a water temperature of 80-90°F, which can be accomplished by illuminating the tank with an incandescent light bulb left on for 18 hours a day.

When leaves and roots appear, carefully remove the plantlet and pot it up in a small container of aquatic plant mix. Some cultivars produce several young plants from one node, and these will have to be teased apart and planted individually. Place the pot in the water garden to a depth of six inches. After a few weeks, when the stems have elongated and all of the leaves are floating on top, lower the water lilies again, up to 16 inches deep.

Generally speaking, vivips take three months to reach maturity, but half that time if you provide them with ideal growing conditions.

With the first frost coming soon, will you tell me which vegetables will survive unprotected in the garden? —T.M., Philadelphia, PA

Answer: Fall, with its cooler temperatures and more abundant moisture, offers excellent growing conditions for many vegetables. Yes, beans, cucumbers, eggplant, musk melon, okra, peppers, pumpkins, squash, sweet corn, sweet potato, and tomatoes will all be damaged by even a light frost, but many other crops will survive. These can best be divided into two categories: semi-hardy and hardy.

Semi-hardy vegetables are those which can survive repeated light frosts in the 30-32 °F range. These include beets, Chinese cabbage, cauliflower, celery, collards, green onions, potatoes, Bibb and leaf lettuce, mustard, parsnips, radishes, salsify, spinach, and Swiss chard. The flavor of some of these, such as collards and parsnips, is, in fact, much improved by exposure to a spell of below-freezing temperature.

Hardy vegetables are those that can survive temperatures as low as 20 °F before finally being killed. These vegetables include cabbage, broccoli, brussels sprouts, carrots, kale, leeks, rutabagas, and turnips. Upon thawing out, these hardy vegetables will continue to grow between freezes.

Remember, too, that even when the tops of such vegetables as carrots and turnips are killed by cold, the roots will remain in good condition if the plants are mulched with a generous layer of insulating material, such as hay or leaves. This will prevent the ground itself from freezing and allow you to harvest the fresh roots as you wish during the winter. You may, however, find that voles discover and enjoy your cache of overwintering produce first. H

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