Gardening Tips

Q. Why can’t I purchase certain types of plants?

Several common landscape plants have made it onto NH and Massachusettes Invasive Non-Native Species List. They are deemed to be invasive due to their rapid growth and ease of propagation, which causes them to crowd out native plants. The best known example of this is Purple Loostrife.

The Burning Bush (Euonymus alatus), Japanese Barberry (Berberis thunbergii) and Norway Maple (Acer Platanoides) are not legal for sale and were prohibited starting January 1, 2007. This includes the popular Crimson King Maple which is actually a Norway Maple, not a Red Maple as many people think.

The following is the list of Currently Prohibited Plants in NH:

  • Tree of Heaven (Ailanthus altissima)
  • Garlic Mustard (Alliaria petiolata)
  • European Barberry (Berberis vulgaris)
  • Oriental Bittersweet (Celastrus orbiculatus)
  • Black Swallow-wort (Cynachum nigrum )
  • Pale Swallow-wort (Cynanchum rossicum)
  • Autumn Olive (Elaegnus umbellata)
  • Giant Hogweed (Heracleum mantegazzianum)
  • Yellow-Flag Iris (Iris pseudacorus)
  • Blunt Leaved Privet (Ligustrum obtusifolium)
  • Showy Bush Honeysuckle (Lonicera x bella)
  • Japanese Honeysuckle (Lonicera japonica)
  • Morrow’s Honeysuckle (Lonicera morrowii)
  • Tatarian Honeysuckle (Lonicera tatarica)
  • Japanese Knotweed (Polygonum cuspidatum)
  • Common Buckthorn (Rhamnus cathartica)
  • Glossy Buckthorn (Rhamnus frangula)
  • Multiflora Rose (Rosa multiflora)
  • Fanwort (Cabomba caroliniana)
  • Variable milfoil (Myriophyllum heterophyllum)
  • Purple loosetrife (Lythrum salicaria)
  • Common Reed (Phragmites australis)

Q. How do I plant my trees/shrubs?

Tips provided by UNH Cooperative Extension

  1. Pre-plant tips
    • Do not pick up plants by their tops; the heavy weight of the soil will injure root hairs.
    • Remove plants from containers just prior to planting, so plants will not sit on the ground in the hot sun.
    • Water plants three hours before planting.
  2. Dig a hole 3 times as wide as the root ball and as deep as the height of the ball. If the plant is balled and burlapped, loosen the burlap and feel the top of the ball for an accurate measurement. When planting a tree make sure the trunk flare remains above ground level. If planted too deep, the roots will suffer from lack of oxygen.
  3. Place a tree in the planting hole with the trunk flare ½ – 1 inch above the surrounding grade to allow for some settling. Place a straight 1” x 1” stake across the hole to help determine planting depth.
  4. Remove all twine, rope, 4. Remove all twine, rope, and as much of the burlap as possible. Synthetic burlap or other non-degradable materials should be completely removed. If the tree ball is in a wire basket, cut away and remove the entire basket.
  5. For containerized plants, inspect the planting media for roots growing in a circle. Correct this situation by freeing and spreading out the roots, roughing up the sides or cutting through the roots in several places. If left unattended the roots will continue to grow in a circle and possibly girdle the plant.
  6. Stabilize the ball by placing good loam in the hole at ½ the ball depth. When needed, mix lime and superphosphate (with no additional fertilizer, manure or compost) with the backfill.
  7. Stake the plant now, but only on very windy sites. Research has shown that staked trees may develop a smaller root system and decreased trunk taper. Trees should not be staked longer than one year.
  8. Water the plant thoroughly until the surrounding soil is saturated to the depth of the root ball. Then allow the soil to settle.
  9. Resume backfilling and tap the soil lightly to eliminate air pockets. Do not “pack” the soil too firmly. Compaction will reduce fine air spaces needed for root development.
  10. When planting is completed, water the planting area deeply.
  11. Place mulch to a depth of 2 to 3 inches (deeper over lighter soils and shallow over heavy soils) tapering inward, so that no mulch touches the trunk. Mulch piled up against the trunk may promote crown rot and create a favorable environment for insects. The most common mulches are pine bark, aged wood chips and pine needles.

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Q. How much and how often should I water?

Probably more than you have been.

One of the biggest mistakes people make is insufficient watering of their new plants. Most people think that because they have an irrigation system for their lawn that also sprays their plant beds, their trees and shrubs are recieving enough water. Lawn watering systems are programed to run one to three times a day for a short period of time, usually between 10 to 20 minutes. This soaks only the first few inches of soil, which is fine for lawns because of their shallow root systems.

Trees and shrubs need to develop deep reaching roots to allow them to withstand drought, extreme cold, and for trees, wind. Shallow watering encourages shallow weak roots. Trees and shrubs require slow, deep watering, reaching down well past the bottom of the root ball. They do best on a drip irrigation system or soaker hose. If that is not an option, place your hose at the base of the plant and turn on the water just enough to start it dripping, and just leave it for several hours. Depending on how hot the weather is, and how much rain we’ve gotten, this may need to be done as often as daily, or as little as twice a week.

Deep watering should continue until the plants go dormant in the fall. This will ensure that they are adequately hydrated until spring.

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Q. When should I prune?

As a general rule of thumb, if the plant blooms in the spring, prune after the blooms die. If it blooms in the summer or fall prune early in the spring just as growth is beginning. Never prune between August and October as plants are preparing for winter. Prune as needed, not all plants need to be pruned every year. You can prune dead or diseased branches at any time.

When you are ready to prune always make the smallest cut possible. Prune for health and shape so you direct the healthy growth of the tree or shrub.

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Q. When should I fertilize?

Make sure to read the directions before applying any fertilizer to your garden. When you first plant use a root stimulate fertilizer. In the spring of the next year, use a slow release granular fertilizer.

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Q. Why doesn’t my hydrangea bloom?

Hydrangeas can fail to bloom for several reasons. First, location is important. They need lots of water in hot weather, and rich soil. The site needs at least morning sun, and while some do well in full sun, most do best with afternoon shade. Full shade is not appropriate for hydrangeas.

The second mistake most gardeners make with hydrangeas is improper pruning. There are many divisions of hydrangeas, some bloom on new growth, others set their blooms on the previous years growth.

Hydrangea paniculata includes the ‘Pee Gee (PG)’ and ‘Tardiva’, and has a pointed dome shaped bloom, mostly white. Hydrangea arborescens includes ‘Annabelle’ and has a broad white dome of flowers. Both are fast growers and bloom on new wood, which means they can be pruned severely in the late winter or early spring and then leave them alone.

Hydrangea quercifolia, also known as the Oakleaf Hydrangea has scalloped leaves likes, full sun to light shade and is slower growing. Oakleafs bloom on OLD wood, and as such are best not pruned. If pruning is absolutely needed, remove the entire stem in late winter to keep the best bloom potential.

Hydrangea macrophylla includes the mopheads and the lacecaps. Most bloom on OLD wood, so minimal pruning should be practiced. There are now several varieties classified as rebloomers, which mean they bloom on old and new growth, so they are generally more forgiving of mistakes. Varieties include ‘Penny Mac, ‘Endless Summer’, ‘Dooley’, ‘David Ramesey’. What gardeners need to be cautious about is that not all macrophyllas, including rebloomers are hardy up here in NH. Many macrophylla varieties will die down to the ground during cold winters, and since there is no old wood for them to bloom on they won’t flower, or will flower poorly.

Hydrangea anomala s. petolaris, aka Climbing Hydrangea bloom on old wood, so pruning a younger plant will eliminate flowers. However, older plants have many stems, so they are tolerant of some shaping.

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Q. How can I prevent common garden diseases?

By Cheryl A. Smith, UNH Cooperative Extension

  1. Practice good sanitation. Start with a clean planting site, free of last year’s crop debris. Debris from the previous season’s crops may harbor diseases and insects
  2. Purchase high quality plants and seeds. Select plants with healthy-looking leaves and strong stems. Avoid collecting seeds from your own plants – fungal diseases are often transmitted on or in seed.
  3. Rotate Crops. Grow your crops in different parts of the garden each year. Be sure not to rotate crops with those in the same plant family (e.g., tomatoes, eggplants, and peppers; cabbage, broccoli and cauliflower).
  4. Do not plant too early. Plant growth may be slowed by cold soil temperatures. Slow-growing plants are more susceptible to attack by disease-causing organisms and insect pests.
  5. Mulch. Mulches prevent soil that may contain disease-causing organisms from splashing onto the plants; mulches also help to retain soil moisture and suppress weeds.
  6. Avoid overcrowding the plants. Crowding creates a moist, humid environment that is favorable for disease development.
  7. Water early in the day. Plants that remain wet throughout the night are more likely to develop disease problems.
  8. Remove diseased leaves, flowers, and fruit as soon as they are noticed. Diseases are easily spread by wind and rain from diseased plant tissues.
  9. Fertilize to promote growth, but avoid over-fertilization, especially with nitrogen. Young, succulent growth is susceptible to attack by many fungi and bacteria.
  10. Try to maintain insect damage at a minimum. Insect wounds provide entry sites for disease-causing organisms.

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Q. What are NH’s planting zones?

NH Planting Zones

NHzonesNHZonesKey

Links

UNH Cooperative Extension

State of NH Department of Agriculture

United States Department of Agriculture

People, Places, Plants Magazine

Perennial Plant Association

American Rhododendron Society

Massachusettes Horticultural Society

Proven Winners

Garden Web

Aggie Horticulture for Kids