What Grows There :: Hugh Conlon, Horticulturalist, Garden Advisor, and Photographer

Agaves Like It Hot, Dry and Sunny

Posted by Hugh on July 1st, 2017

Agaves in Burbank, CA

Variegated agave in sidewalk planting in Burbank, CA

Agaves (Agave spp.) are long-leaved succulent landscape plants. These native perennial succulents grow in desert-like environments (USDA hardiness zones 8 and warmer). Plants grow in a rosette form with long their fleshy leaves frequently tipped with one or more sharp spines and a prominent bloom spike with cup shaped flowers. Most are native to the Southwest U.S. and Mexico.

Agaves are exceptionally drought tolerant and ideal for xeric gardens. Temperature hardiness, sunlight, and soil drainage are the three key components to successfully growing agaves. Agave have a large tap root and do not transplant well, so carefully select an appropriate site where to plant. The majority of the roots are surface roots and do not require a deep hole if planted when young.

Porous, well-drained soil is an absolute must! When planting in clay soils, deeply amend bed or container soil with coarse sand or pea gravel in a 50:50 ratio. Water the plant diligently the first week after planting and gradually wean it back to 2-3 times monthly in containers, all depending on season of the year and outdoor air temps.

Never overwater agaves! They are famous for their low water use. In early spring apply a slow release fertilizer such as Osmocote™ or Nutrikote™. This should supply nutrient needs for the entire year.

Most agaves naturally dieback after blooming. They form new plants (“pups” or offshoots) at the base of the “mother” plant. Many gardeners opt to remove the spent floral spike with long handle lopper pruners to avoid their sharp spines. Agaves should be re-potted every year, usually in the spring in new media. Prune off old lower leaves if they detract from the plant’s beauty.

Non-hardy types are moved indoors or in an unheated garage where temps drop below 37°F and grown in an east facing window. Over the winter months reduce frequency of watering intervals and do not fertilize.

Agaves are deer-resistant. The tall bloom stalks attract hummingbirds.

Agave parryi var.

Four popular agaves:

Century plant (Agave americana) – a lovely flower (inflorescence) and leaves have a white stripe running along the center.

Parry’s or Mescal agave (Agave parryi) – an attractive slow growing compact form that measures 2-3 feet across. Leaves are grey green tipped with a spine (zone 7 hardy).

Ocahui Century Plant (Agave ocahui ) (zone 7b -10) – this 2-3 feet wide ball-shaped agave has attractive rigid dark green leaf blades with attractive red margins and sharp flexible spines. Bloom spike will eventually reach nearly 15 feet tall with yellow-green flowers.

Black spine agave (Agave macroacantha) – a medium sized rosette form and 1 ½ feet long thick grey green leaves, each tipped with a 1-inch long sharp black spine. Small grey and red flowers form on sturdy 7-10 feet high stems.

Tidying Perennials After Blooming Is Over

Posted by Hugh on May 15th, 2017

Clean-up of Old Blooms in Lambs ears (Stachys byzantina)

Clean-up Old Blooms in Lambs ears (Stachys byzantina)

Heuchera flower scapes

“Deadheading”, the practice of removing the old or spent flowers, can be utilized to improve the appearance of many perennials. These perennials do not rebloom after deadheading, but plants look alot better after the cleanup. Daylilies (Hemerocallis cv.), coral bells* (Heuchera spp.), and hostas (Hosta spp.) are prime examples of perennials that benefit from clean up after deadheading.

The flower or plume stalks of many perennials are highly ornamental and can be left to enjoy. Many ornamental grasses are examples here. On others, you risk the dispersal of unwanted seeds which frequently become next year’s weed problem in your garden.

Gardeners opt to remove flower stalks to put all the plant’s energy into the foliage. The following list is not complete, but includes most popular perennials.

Bear’s breeches (Acanthus spinosa)

Bugbane (Actaea podophylla)

Bishop’s weed, goutweed (Aegopodium podagraria)

Japanese anemone (Anemone × hybrida)

Lady’s mantle (Alchemilla mollis)

Goat’s beard (Aruncus dioicus)

Astilbe, False spirea (Astilbe spp.)

False indigo (Baptisia australis)

Bergenia (Bergenia cordifolia)

Queen of the Meadow, Meadowsweet (Filipendula ulmaria)

Cranesbill, Wild geranium (Geranium spp.)

Lenten Rose or Hellebore (Helleborus x orientalis)

Daylilies (Hemerocallis spp.)

Coral bells (Heuchera spp.)*

Rose mallow (Hibiscus moscheutos)

Hostas (Hosta spp.)

Irises (Iris spp.)

Leopard plant, Ligularia (Ligularia spp.)

Catmint (Nepeta × faassenii)

Herbaceous Peony (Paeonia spp.)

Obedient plant (Physostegia virginiana)

Lungwort (Pulmonaria spp.)

Lambs’ ears (Stachys byzantina)

* There are two forms of coral bells, those with showy flowers (average foliage) and those with lush colorful foliage (non-showy flowers).

After deadheading apply a water soluble fertilizer such as Miracle-Gro™ or Schultz™. This is good time to clean up the bed, remove weeds, and add organic mulch. If ground is dry, water deeply the perennial bed by irrigating overhead (equivalent of 1 ½ inches of rainfall) for 3 – 4 hours.

Keep Your Eye on Red Buckeye

Posted by Hugh on March 25th, 2017

Red buckeye (Aesculus pavia)

Red buckeye (Aesculus pavia) is shrubby or low branching tree maturing to a 15 – 20 feet in height and spread. This southeastern U. S. native is becoming more recognizable as a good choice as a landscape tree for a small urban garden. Plant the tree in either full to partial sunlight and in average well-drained soil.

A tree may develop flowers when it is young in late April and May. Numerous 5 to 9 inches long floral heads sit at branch tips like decorative candles. Bloom count is highest in full day sun. Flowers open slightly before leaf emergence. Flower color on individual trees varies from dark pink to scarlet red. A yellow flowering form is known to exist. Hummingbirds arrive in time to pollinate the individual tubular blossoms.

Lovely palmate compound dark green leaves clothe the branches in spring thru early summer. In late September the broad seed pods split open exposing polished dark buckeye seeds; they drop from the tree, and are quickly grabbed up by squirrels and other garden critters. Don’t be surprised to find a young seedling or two germinating somewhere in the landscape in the years ahead.

Several disease and insect problems riddle the foliage; dry and hot summer weather will often scorch leaf edges unless irrigated weekly. Leaves succumb to the disease and weather onslaught resulting in premature leaf loss beginning in mid-August. Count on no autumn foliage color as branches are typically bare. Spraying pesticides to prevent diseases and insects is unnecessary. New flowers and foliage emerge unharmed the following spring. Deer and rabbits do not trouble this tree.

Pruning, if needed, is performed in mid-spring, right after flowering. Feed the tree lightly with 10-10-10 fertilizer (or equivalent) either before or following spring bloom.

Enjoy The Double Soft Pink Flowers of Kwanzan Cherry

Posted by Hugh on March 4th, 2017

‘Kwanzan’ Cherry Tree

Soft pink double flowers

Kwanzan cherry (Prunus serrulata ‘Kwanzan’) is a commonly planted Oriental cherry in the U.S. (USDA hardiness zones 5 – 8). It’s most often utilized as a small 25 to 35 foot tall flowering deciduous tree in an open lawn, patio. and deck setting for its cool summer shade. It is a 4-season specimen and should be located where it can be viewed year-round.

Kwanzan cherry is in glorious flower in mid-spring and is frequently planted along with Yoshino Cherry (P. x yedoense) in Washington, D.C. and Macon, Georgia for their annual Cherry Blossom Festivals. Yoshino cherry produces abundant single pale pink cherry blossoms a full week or two before Kwanzan. The later blooming Kwanzan is less prone to late spring frosts, which is so important to festival planners.

The 2-inch diameter powder-puff pink flowers are comprised of 24 – 28 petals, with no sexual floral parts. Therefore tree will rarely produce fruits. Flower clusters of 3-5 blossoms develop at each node. New spring leaves are bronze colored at the start and turn to a medium green within a few days. In autumn leaves turn yellow, orange, or copper colored. A unique way to identify Kwanzan is the pair of large distinctive glands at the base of each leaf blade.

Site selection is very important in growing Kwanzan cherry. It performs best in full sun and in a well-drained fertile soil. Hot, dry summers can shorten a tree’s life span. Annual pruning is absolutely essential and should be performed immediately after flowering. Remove dead, weak, or sickly branches, including those that may be infested with scales and other serious insect pests.

Kwanzan cherries are prone to a long list of insect and disease problems, including cankers, black knot, leaf spot, die back, leaf curl, powdery mildew, root rot and fireblight. Potential insects include aphids, scales, borers, leaf hoppers, caterpillars, tent caterpillars, Japanese beetles and spider mites. Canker, borers and virus can be particularly troublesome under high stress environmental conditions such as hot droughty sites.

Powdery Mildew Disease Resistant Cultivars

Posted by Hugh on January 15th, 2017

Powdery mildew on herbaceous peony

Powdery mildew on Garden Phlox

Gardeners have learned to associate certain plants with a troublesome disease(s). Powdery and downy mildews have become epidemic in many regions of the U.S. Best ways for managing mildew diseases are prevention, good cultural practices, and spraying.. First, avoid planting susceptible cultivars. Plant in the proper location and space plants far enough apart so they’re not touching. Surrounding vegetation should not block air movement through the garden.

Follow good cultural practices such as reducing or eliminating overhead irrigation practices. Fertilize to optimize plant health, but avoid over-fertilization with nitrogen as it stimulates young, succulent growth which can be more susceptible to infection.

Some moderately susceptible cultivars may require protection with fungicide sprays, particularly if environmental conditions are highly favorable for onset of mildew diseases. Dig up and eliminate susceptible cultivars of lilac, roses, crape myrtle, impatiens, zinnias or summer phloxes. Plant breeders continue to provide gardeners with better disease resistant cultivars. In recent years, notable examples of resistant plants include:

Crape myrtles – ‘Catawba’, ‘Hopi’, ‘Cherokee’
Crabapples – ‘Prairifire’, ‘Sugar Tyme’, lots others
Dogwood (Cornus florida)– ‘Cherokee Brave’, ‘Appalachian Joy’, ‘Appalachian Snow’, ‘Appalachian Mist’

Dogwood hybrids (C. florida x C. kousa) – ‘Stellar Pink’, ‘Stardust’, ‘Galaxy’, ‘Constellation’ , ‘Aurora’
Sycamore – ‘Columbia’, ‘Liberty’, Yarwood, Exclamation™
Summer phlox – ‘David’, ‘Robert Poore’, ‘Delta Snow’, ‘Speed Limit 45’
Lilac – ‘Bloomerang’, ‘Betsy Ross’, S. meyeri ‘Miss Kim’, S. pekinensis

Monardas (beebalm) – ‘Marshall’s Delight’, ‘Blaustrumph’, ‘Colrain Red’.

Rhododendrons – R. yakushimanum, R. macrophyllum, R. ‘Nova Zembla,’ R. ‘Palestrina’
Roses – Simplicity™ and Meidiland™ roses, Rosa rugosa varieties
Zinnias – Z. angustifolius ‘Profusion or Zahara series; Pulcino and African varieties

One final thought: if foliage infections break out on garden plants in very late summer or fall, spraying a preventative fungicide is generally not necessary or impractical. Instead, practice good garden sanitation, a thorough clean-up of infected leaves and stems. For infected annuals and perennials, gather up infected debris and discard. Do not add it to a compost pile, but throw it curbside for pickup or add to a burn pile, obtaining the proper burn permits.

Five Simple Pruning Tips For DIYers

Posted by Hugh on January 11th, 2017

March Rejuvenated viburnum 3 months after cutback

Small Dramm pruner perfect for small 1/4 inch pruning cuts

Gardeners are frequently scared about making pruning mistakes. There are lots of gardening books filled with lots of before and after photos. Let’s face facts…your yard tree or shrub does look like the ones pictured in the pruning book.

Here are my simple 5 steps for pruning:

Why and When to prune: You can prune a tree or shrub any day of the year. The best time is generally in late winter. Choose a comfortable weather day to work outdoors so you’re not in a hurry. Remove low growing branches in any month. Branches that are dead, broken, infested with scale insects, or diseased can also be sawed or lopped off anytime. If the job involves major pruning, e.g. 30% of branches removed, spring or summer pruning is best time.
Flowering shrubs or trees — when do they bloom? Spring flowering shrubs and trees are best pruned immediately after or within one month after flowering. Can’t wait?…then prune when you’re ready. Crabapples, ornamental cherries, redbuds, dogwoods, azaleas, lilacs, forsythias, and spireas bloom on old wood in spring. Summer flowering woody plants bloom on new wood. Examples include most (not all) hydrangeas, chaste trees (Vitex), crape myrtles, althea (Hibiscus), butterfly bush (Buddleia), and roses.
Make the big cuts first. Take your time! Observe the tree from several points to determine the best cuts. Making many small cuts is okay, but they’re a lot more time consuming. Small pruning cuts heal faster than bigger ones. Completely rejuvenated shrubs are cut back 6 – 12 inches above the ground. Applying pruning wound paint is not necessary.
Use sharp pruning tools — Don’t plan to do all work in 1 year. If the tree has been neglected for several years, it may take 3-4 years to bring back desired shape and health. To repeat, don’t remove more 30% of branches in any one year.
Large shade trees — hire a certified arborist who should be properly insured and licensed. Maples, oaks, lindens, elms, birches, and others should be pruned every 5 years. Tree topping should be avoided as this practice results in a tree potentially more hazardous.

Types of Garden Irrigation

Posted by Hugh on January 7th, 2017

Irrigation system

Tree irrigation

These days there are lots of choices in watering gardens, individual containers, and newly planted trees. Before setting your flowers or veggies, install drip lines or soaker hoses. These systems are the most efficient method of watering and put less hurt on your water bill.

Drip systems deliver water at ground level and do not wet the foliage, limit evaporation loss, and result in less foliar disease infections. Soaker hoses and simple drip systems are available at full-service garden centers. They save water because it doesn’t end up on sidewalks or driveways.

Drip irrigation, also called “trickle irrigation,” allows you to custom-design a watering system for flower, vegetable, small fruit beds, and containers. Water flows through flexible tubing and out of emitters. Spacing for emitters preset by the manufacturer or set by the gardener. Always inspect emitters as they may clog up or rabbits and other critters may bite into the water line. Install a filter or strainer at the faucet to catch all debris and dirt. Clean out the filters every few weeks.

Over a 12- 24 hour intervals, drip or soaker systems deliver a column of water to a depth of 12 inches or more into the soil. This is adequate for most plants from shallow rooted annuals to deep rooted trees.

Tree watering bag

What about oscillating or overhead sprinklers? They are best confined to your lawn and not your flower or vegetable garden. Sprinklers provide an even supply of water quickly, but have two drawbacks. A sprinkler usually wastes water, spilling on sidewalks and driveways. Plant foliage gets soaked, and this may result in mildew and leaf spot disease infections.

While you’re away, an automatic watering systems may be what you need. All you do is set a timer that is attached to the hose or faucet. Two types, mechanical and electrical timers, are sold. Just attach timer to a faucet and set it to turn water on and off. Electronic timers offers the added benefit of watering at different times and days of the week.

Facts About Garden Watering – How Much And When

Posted by Hugh on November 13th, 2016

Tripod rotating sprinkler over new lawn seeding

Irrigation system

Modern gardeners are using more efficient drip irrigation or soaker hoses. Water bills are less than overhead or oscillating systems. You may opt to attach the hose to an automatic timer so you can irrigate in absentia. Water goes on and off anytime you select.

In garden beds water plants deeply once weekly rather than a little bit every day. During the summer months, daily or twice-daily watering may be needed for annuals and perennials growing in hanging baskets, window boxes. Newly planted and large container-grown small trees and shrubs may need a drink.

Over a dry summer, long season vegetables demand deep watering to yield tomatoes, squash, pumpkins, cucumbers, etal. Rhubarb, asparagus, and many perennial herbs need summer moisture to survive cold winters. In late fall rhododendrons, azaleas, blueberries, and other shallow rooted plants should be deeply irrigated before heading into a dry cold winter.

How much water do garden plants require? Most summer annuals need an inch of water weekly—either supplied by natural rainfall or through a hose. Never waste water, no matter how full your city’s reservoir supply; don’t send water down the driveway or street gutter. Mulching plants aids to lower water use.

By mid-July, plants growing in containers require almost daily watering. Some container grown plants like daphnes or hostas are not forgiving if you miss a scheduled waterings, while agaves don’t seem to care. Bigleaf hydrangeas (Hydrangea macrophylla) or ligularias may be seen wilting in the mid-day sun, but fully recover by evening. Repotting plants into larger containers also helps.

Early morning is the best time to water by hand or by an oscillating sprinkler. Plant foliage has adequate time to dry off, reducing potential problems with fungal and bacterial diseases. Disease causing spores require moisture on the leaf surfaces. Snail and slug injury is worse by irrigating in late day or at night.

Finally, the more that you irrigate, nutrients, particularly nitrogen, are leached out of the root zone. New fertilizer must be applied for plants to continue growing and not suffer from nutrient deficiencies. Overwatering leads to root and crown rot problems.

Seven Ideas for Managing Mosses in Lawn Areas

Posted by Hugh on September 30th, 2016

Lawn moss (photo by Dr. Tom Samples, Extension Turf Specialist, Univ. of Tennessee, Knoxville

Lawn moss (Photo by Tom Samples)

Mosses, over 14,000 species of them worldwide, are major competitors with lawn grasses in certain landscape situations. They belong to their own plant family. They photosynthesize and draw moisture from tiny rhizoids (primitive root systems). They do not compete for soil nutrients with lawn grasses. Some can live in full sun, other kinds in shade areas. Mosses hug the ground, below the cutting height of lawnmowers.

Liming: Many mosses grow well in acidic soils (pH<7.0). Their presence in lawns does not mean that a lime application is necessary. A soil test can this determination. A broadcast application of granular or pelletized dolomitic or calcitic lime using a spreader is better method compared to a pulverized (powder) lime source.

Fertilization: Poor soil fertility favors the development of moss. Improve the competitive of lawn grasses by fertilizing at the proper time of year. For cool season grasses (Kentucky bluegrass, tall and fine fescues) species, spring and fall applications utilizing high nitrogen (N) fertilizer is a practical approach. For warm season (burmuda, zoysia), late spring and summer applications are best times.

Improving Soil Drainage and Aeration: Compacted soils favor growth of moss over grass, particularly in irrigated areas and excessive periods of rainfall. Core aerification of areas with wet clayey soils improves soil drainage to favor turf over moss.

Pruning: Trees compete with lawn grasses for light, water, and nutrients. Shade keeps soil moist which favors growth of moss. Selective removal of dense branching improves sunlight penetration and air circulation, which causes soil to dry out more rapidly favoring lawns over mosses.

Raking Up Fallen Tree Leaves: quick removal from the ground will dry out the soil surface quickly and improve light and air circulation.

Chemical Suppression of Mosses: the following products are sold at garden centers:

Iron sulfate
Ferrous ammonium sulfate
Anti-moss products containing potassium salts

Alternative perennial ground covers including mosses instead of lawn grasses in heavily shaded areas.

Late Summer Bulbous Beauties – Spider Lily and Fall Crocus

Posted by Hugh on August 26th, 2016

Spider Lily Pops Up in Weedy Lawn

Colchicum (fall crocus)

Spider lilies (Lycoris radiata) go by a number of colloquial names including resurrection flower, surprise lily, and naked ladies. Naked 1-2 foot tall flower scapes bear 4-6 bright coral-red flowers. Each 2- inch long flower exhibit reflexed tepals and long protruding stamens resembling spider legs (common name “spider lilies”).

Almost overnight, the leafless flower spikes arise in late summer. Several weeks later, strap-like gray-green leaves arise where the floral stalks had been and have now disappeared. Foliage stays evergreen through the winter to feed the below ground bulbs before dying back in spring.

Plant bulbs 9 -12 inches apart in late spring or early fall. Plant them shallow with the neck of the bulb just peaking through the ground. Plants will naturalize by bulb-offsets and form small colonies over time in the southeastern U. S. (USDA hardiness zones 6-10).

Autumn crocus (Colchicum autumnale) is native to Great Britain and Ireland (USDA hardiness zones 4-7). Colchicums bloom in the earliest days of fall often coming up in late August. In late spring, plants send up 4-6 dark green lance-shaped leaves, some which 10- 14 inches long. The foliage yellows and dies down by summer into dormancy. Flower stems with no leaves emerge from the ground to 4-6 inches tall in late summer to early fall bearing goblet-shaped 3 inch long flowers. Flower colors vary from purple to pink to lilac. Weak flower stems tend to flop.

Plant corms 3 inches deep and 6 inches apart in August for bloom that occurs in the same year and many years following. To move or expand an existing planting, mid- to late-summer in the best time.

Both Lycoris and Colchicum grow in organically rich, medium moisture, well-drained soils in full to partial sunlight. Plants respond negatively to soil moisture, preferring dry soils during the summer dormant season and moderate soil moisture during bloom period in late summer. Provide a minimum of 4-5 hours of sunlight for high flower count.

Colchicums (autumn crocus) are not be confused with the true autumn crocus or saffron crocus (Crocus sativus) that also bloom around the same time. The latter are edible and closely related to the spring-flowering crocuses. All plant parts of colchicum are highly poisonous

Neither lycoris or colchicums have serious insect or disease problems. In a wet summer slugs and snails may become significant troublesome pests.