Summer garden tasks

We have had a fantastic spring for planting.  Frequent rains have provided regular water to anything you planted this spring.  It is about time to wrap up planting for the season.  Of course, you can plant all summer but you will have to be much more vigilant about watering newly planted trees, shrubs and perennials as the weather gets warmer and the rainfall less frequent (probably if we are going to have a normal Delaware summer).  If the weather gets really dry, you will need to water most of the plants you put in this spring.  Plants shouldn’t be considered fully established until they have gone through at least one complete growing season.  Large trees may take several years to become fully established.   Consider using a gator bag on newly planted trees.  Fill up the bag with a hose and the water will trickle out slowly allowing the soil to absorb all the water and making it available to the tree roots.  The same thing can be accomplished with a five gallon bucket that has a few holes punched in the bottom.  You can also water using a hose set at trickle, but that takes much more time and effort to keep moving the hose once the soil has become saturated.  Do not apply water faster than what your soil can absorb.  Water that runs off is wasted and can cause erosion and particulate pollution in nearby waterways.

With the bulk of your planting completed, it is time to turn your gardening attention to taking care of your plants.  Early summer is the time to prune spring flowering shrubs.  Always cut branches back to another branch or bud, never leaving a branch stump.  Remove the longest branches to reduce the size of your shrubs but maintain their natural form.  As perennials finish blooming, remove spent flowers to conserve the plant’s resources. Some perennials and shrubs will even re-bloom if cut back after flowering and before seed heads develop. But, if you want to encourage seeding to spread a ground cover or plant you want to fill into a larger space, then leave seed heads on and allow seeds to mature.  You might also want to leave seed heads to feed birds.  Gold finches love cup plant (Silphium perfoliatum) seeds, but I am always torn about leaving seeds because this plant seeds into the garden prolifically. Cut back fall-blooming plants, like mums and asters, now to encourage a compact habit when they bloom in August to October.

If you are managing a meadow, you may want to cut the meadow back now (mid to late June) to keep grasses from flopping later in the season.  We have had a wet spring, so grasses will be at the taller end of their normal range and may flop unless they are cut back now.  If you are cutting back your meadow, mow it to a height of 6-8 inches.  It will look sloppy for a few days, but the grasses and perennials in the meadow will quickly regrow and your meadow will be dense and lush again soon.  You should be mowing paths through your meadow to provide access and a “cue of care.”  You can mow the path on the same schedule as the rest of your lawn (approximately weekly) and mow one mower width on each side of the path every several weeks.  That will also help to keep the meadow looking neat and tidy and keep the path clear of flopping grasses.

This cup plant (tall yellow flower on the right) will feed gold finches but it will also seed into the garden, so be careful.

This cup plant (tall yellow flower on the right) will feed gold finches but it will also seed into the garden, so be careful.

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Weeding—does it ever end?

Weeding is one of those gardening tasks that some people find peaceful and enjoyable and others HATE!  Weeding is a component of gardening but it doesn’t have to consume all your gardening time.  Here are some strategies to help control weeds:

Use groundcover in your landscape beds to compete with weeds.  Most landscapes should have three layers—tree layer, shrub layer and groundcover.  When landscape designers, draw landscape plans, they tend to draw in large circles for the trees and smaller shrub circles, but often neglect to specify plants below the shrubs to cover the ground.  Few shrubs branch to the ground completely and therefore require a layer of plants below them to prevent weeds from growing in the bed.  The University of Delaware gets a lot of mileage from lilyturf (Liriope spicata) as a tough groundcover that out competes most weeds.  But, if you want more variety, you can try lamb’s ears (Stachys byzantina), bugleweed (Ajuga reptans), sweet woodruff (Galium odoratum), Allegheny pachysandra (Pachysandra procumbens)—a great native that takes a little while to establish but fills in thickly once it gets going, Christmas fern (Polystichum aristicoides) or barrenwort  (Epimedium sp.)—a great plant for dry shade.   Also consider planting perennials to fill in spaces rather than just shrubs.  Catmint (Nepeta  x faassenii ‘Walker’s Low’) is a great perennial that grows densely and out competes most weeds.  It is blooming now in Delaware gardens.  If you have a large space to fill, you might try mountain mint (Pycnanthemum muticum).  It is a vigorous grower and could become a problem in a small garden but its mid-summer flowers last until September in the form of silvery bracts.  It is also one of the best nectar sources for butterflies and bees so it is great to include in a pollinator garden.

Another weed control strategy is to cover the landscape bed with mulch.  Mulch will prevent light from reaching the soil, so few annual weeds are able to germinate.  You can generate your own mulch with composted yard waste and ground up leaves.  You can also buy leaf mulch or hardwood bark mulch.  Use mulch as a temporary feature, until your plants fill in or at the edges of beds to differentiate the landscape bed from the lawn.

Herbicides can be used carefully to control weeds as well.  Pre-emergent herbicides are used to control annual weeds before they emerge, by setting up an herbicide barrier in the soil.  It is a little late to apply a pre-emergent product this year, but something to consider for landscape beds next year.  Selective post-emergent herbicides can be used to control grass in landscape beds or broad-leaved weeds in lawns.  You can also use a glyphosate product (Roundup is one example) to spot spray weeds, but be careful because glyphosate kills most green plant tissue it touches.  It is easy to get spray drift and damage desirable plants.

Barrenwort (Epimedium sp.) in flower at the Delaware Center for Horticulture.

Barrenwort (Epimedium sp.) in flower at the Delaware Center for Horticulture.

Allegheny spurge (Pachysandra procumbens) on UD's campus.

Allegheny spurge (Pachysandra procumbens) on UD’s campus.

Finally, readjust your attitude about weeding.  Bring a cushion and a glass of iced tea outdoors with you.  Put on a good pair of gardening gloves.  Have a weed bucket nearby and spend a little time each weekend or evening relaxing in your garden and pulling up a few weeds.

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Hydrangeas – Star of the Summer Garden

Summer?  Wait, we are just starting to enjoy spring weather.  But, now is the time to buy and plant trees, shrubs and perennials to enjoy this summer.  Do big blue and pink globes of hydrangea flowers remind you of your grandmother’s garden?  If so, come and get a dose of nostalgia or enjoy lots of trendy new hydrangeas .  Hydrangea is the featured plant of this year’s UDBG sale and is certainly a trendy plant in the industry.  This genus includes a wide range of plants from vines to large shrubs.

Bigleaf hydrangea  (Hydrangea macrophylla) is the old fashioned plant most of us remember from Grandma’s garden.  This species produces large balls of sterile flowers that are either pink in basic to neutral soils or blue in acidic soils.  The added fun of changing soil pH to change the flower color makes this plant unique.  There are also lacecap varieties in this group that have a ring of sterile flowers around a center of fertile flowers, looking like a lacecap (duh!).

Panicle hydrangea (Hydrangea paniculata) is another old time favorite. The flower head forms a large cone of sterile flowers with lots of fertile flowers in the interior.  Most are white, fading to pink but some new cultivars fade to pink more quickly and retain the pink color longer, even as dried flowers.  Panicle hydrangeas bloom on new wood, so they should be pruned in late winter to early spring, for the best blooms.

If you want a native hydrangea, look for smooth hydrangea (Hydrangea arborescens) or oakleaf hydrangea (Hydrangea quercifolia).  Smooth hydrangea is not super showy as the straight species, but several showy cultivars are available.  Oakleaf hydrangea is a popular coarse-textured plant with exfoliating bark and large globose flowers.  Oakleaf hydrangea flowers are white, fading to pink and often hang on the plant all winter, providing interest and structure to the winter garden.  Leaves in this species turn a beautiful burgundy color in the fall.

If vines are your thing, there is even a hydrangea vine (Hydrangea anomola spp. petiolaris) that adheres to rough surfaces such as masonry and tree bark.  This vine has numerous white flat-topped flower clusters ringed by white sterile flowers in the summer.  Use it on a wall next to a walkway where there isn’t room for a shrub or tree.

Hydrangea flowers are great for cutting and drying.  Plants tolerate a range of conditions from full sun to full shade depending on the species and cultivar.  Many new cultivars have been selected for smaller sized plants with different flower colors and shapes.  The UDBG Plant Sale was the last weekend in April but you can still access the catalog for a complete listing and description of lots of great hydrangeas as well as many other plants. Look at the online plant sale catalog by visiting this URL. (

Spigelia marilandica and Hydrangea quercifolia – Oakleaf hydrangea with a native perennial, Indian pink, in the University of Delaware Botanic Garden.

Spigelia marilandica and Hydrangea quercifolia – Oakleaf hydrangea with a native perennial, Indian pink, in the University of Delaware Botanic Garden.

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When to Fertilize Your Lawn

A beautiful green lawn, like this gathering space at Chanticleer Gardens in Radnor, PA, can be achieved with fall fertilization.

A beautiful green lawn, like this gathering space at Chanticleer Gardens in Radnor, PA, can be achieved with fall fertilization.

Spring is here (even though it doesn’t feel quite like spring).  So, that means it is time to fertilize your lawn, right?  Wrong.  It is not necessary to fertilize your lawn in the spring.  In fact, it is much better to fertilize in the fall.  Grass puts its energy into growing leaves in the spring, which means more mowing.  But, grass puts energy into root growth in the fall, which means healthier, more resilient plants.  It is OK to add about ½ pound of nitrogen per 1000 square feet of lawn in April, which translates to 5 lbs of 10-10-10 fertilizer or 2 pounds of 25-5-10 fertilizer.  Some people like to have their lawn green up more quickly or at the same time as their neighbors.  This amount of nitrogen will be readily used by the lawn as long as it is not applied right before a severe rainfall.  But, it is not really necessary for a healthy lawn.  If you want to manage your lawn as simply as possible, apply one application of a slow release fertilizer in September, using 2 pounds of nitrogen per 1000 square feet (12 ½ pounds of 16-3-7 fertilizer).   If you don’t want to use a slow release fertilizer product, you can split the application of fertilizer into two applications-one in August/September and one in October/November.  If this sounds complicated, watch the videos on the livable lawns website for a simple explanation (

But wait, phosphorus is also an issue in lawn fertilizer.  That is the second number in the analysis (N-P-K).  Many soils in Delaware already contain plenty of phosphorus and it isn’t necessary to add anymore.  In fact, extra phosphorus can run off and pollute our rivers and streams.  So, it is a good idea to take a soil test before you fertilize.  Find out if you have enough phosphorus and if so, use a low phosphorus or phosphorus-free fertilizer on your lawn.  Some neighborhoods in Delaware, where phosphorus in the soil is high, simply require phosphorus-free fertilizer.

A number of Delaware environmental agencies want to encourage you to apply the right amount of fertilizer to your lawn at the right time, as well as increase the number of native trees in Delaware’s suburban landscape, so keep your eyes open for a new Livable Lawns Program for homeowners.  You can hire a certified livable lawn company to manage your lawn maintenance (see for the certified company nearest you).  Or you can manage your own lawn following the livable lawns guidelines (  If you become a certified livable lawn, Livable Lawns will provide a $100 voucher to purchase native trees from participating retailers to plant on your property.  Check the Livable Lawns website ( in late April for details about this exciting new program.

Spring is also the time people apply preemergent herbicides to control crabgrass in their lawns.  Crabgrass is an annual grass that germinates from seed each spring.  By applying a preemergent herbicide, you set up a chemical barrier that kills newly germinated crabgrass seedlings before they emerge from the soil.  The best way to prevent crabgrass is to have a thick, healthy lawn, which you can get by fertilizing in the fall.  The dense lawn prevents light, needed for germination, from reaching the crabgrass seeds.  If crabgrass has been a problem in the past, it may be necessary to use an herbicide this year to control the crabgrass and start your fall fertilization program in September.  You do not need to buy a product that contains both fertilizer and crabgrass preventer, although that is what many lawn and garden stores sell.  Look a little more closely for a product that contains just a preemergent crabgrass herbicide.

The bottom line is before you reach for that bag of fertilizer this spring, consider switching to a more sustainable lawn management program.

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Plants of the Year

Plants of the Year – 2014

Lots of organizations designate special plants of the year to highlight plants with great features and help gardeners choose plants to add to their landscape.  Here are some of the choices for 2014.

The Delaware Nursery and Landscape Association (DNLA) has been choosing a woody plant (tree or shrub) and a herbaceous plant (one that dies back to the ground each year) yearly to promote to Delaware gardeners.  A selection committee that includes industry members, garden writers, university professors, local landscape designers, and local landscape consultants comes up with a list of plants that meet the criteria each year.  The plants must be available in the nursery trade (nothing is more frustrating than reading about a plant and then not being able to find it to buy and plant in your garden).  They must also grow well in our region, have few pest and disease problems, provide an interesting or showy element to the garden and be somewhat underused in the Delaware landscape.  What is the point in promoting a plant that is already overused!  Then the DNLA board of directors’ votes on the plants they think best meet the criteria from those nominated plants.  Everyone has their favorites and the discussion can get sticky at times, but the process routinely churns out great plants that Delaware gardeners will enjoy in their home landscapers.  The two choices for 2014 are:

 Paperbark Maple (Acer griseum) – This small tree grows in moist, well-drained soil in full sun to partial shade. It has an oval to oval-rounded habit and is known for its peeling, cinnamon to reddish brown bark. Trifoliate leaves are dark green, but turn red in the fall. Its seed is a two winged samara.  It has no serious disease or pest problems. Paperbark maple is a slow grower (6 inches – 12 inches per year) and makes an excellent tree specimen tree for small properties. It is appropriate as an understory tree in a woodland garden or as a specimen in many locations around the home.

Christmas Fern (Polystichum acrostichoides ) – This fern is best grown in organically rich, dry to medium moisture, well-drained soils in part shade to full shade. It will tolerate a dry site better than most ferns. Christmas fern is a local native that can be found on both dry and moist wooded slopes, moist banks and ravines. It typically grows in a fountain-like clump to 2′ tall and features leathery, lance-shaped, evergreen (green at Christmas time as the common name suggests) fronds. While it is considered evergreen and provides winter interest (unless the ground is covered in snow!), the old foliage is pretty beaten down by the end of the winter and gardeners will be looking forward to young fiddleheads emerging in spring. There are no serious insect or disease problems. But, avoid planting in poorly drained soils, where crown rot can be a problem, particularly in winter. Christmas fern looks great in woodland gardens, shade gardens or shady areas of borders, wild or native plant gardens. It can be planted in shady areas along walls or foundations. Christmas fern is a good plant for massing on slopes (including dryish, rocky ones) to help combat soil erosion.  Another big benefit in our area is like all ferns, Christmas fern is deer resistant.

 The Society of Municipal Arborists has named Persian ironwood (Parrotia persica ‘Vanessa’) as their 2014 street tree winner.  Parrotia was chosen for its many merits including resistance to drought and pests, upright habit, hardiness, slow growing smaller size, fabulous fall color and interesting bark.

Northwind Switchgrass with Juniper

The Perennial Plant Association also picks a plant of the year and for 2014 that plant is Northwind switchgrass (Panicum virgatum ‘Northwind’). This tall ornamental switchgrass has a distinct vertical habit. It is the sturdiest of the cultivated switchgrasses – guaranteed not to flop. Olive-green to blue-green foliage turns tan in the fall and along with its airy flower panicles provide great winter interest.  By the spring, this still-bold foliage has almost a white color and looks striking when combined with an evergreen, like Eastern red cedar (Juniperus virginiana). It looks so good, it might be hard to cut back the foliage in the spring to make room the new growth.  But, never fear, Northwind switchgrass will grow back quickly and provide a great backdrop for other plants in the garden.

The National Garden Bureau picks a flower, vegetable and perennial each year to showcase and the 2014 choices are petunia, cucumber and Echinacea (coneflower).  There are many great new coneflower cultivars available.  In 2009, Mt. Cuba Center conducted an evaluation of many Echinacea species and cultivars for our region.  A copy of the results can be found at

Not be outdone, the International herb association also picks an Herb of the Year™.  The selected herb must be outstanding in at least two of the major herb categories—medicinal, culinary or decorative.  The 2014 Herb of the Year™ is Artemisia. This diverse herb family contains many strikingly different plants, from the highly decorative Artemisia ludoviciana ‘Silver King’ to the delicious and tender French tarragon (Artemisia dracunculus ‘Sativa’). Artemisia has a long history, prominent in folklore, its virtues used in numerous ways: to protect and heal, create tasty beverages and foods, decorate the home and work its magical properties.

Finally, 2014 in the Chinese Year of the Horse.  What does that mean for plant lovers?  How about planting a horse chestnut in your garden?  Horse chestnut (Aesculus hippocastanum) is a large tree native to the Balkans that has palmately compound leaves and very showy flowers born in upright panicles.  Our native Aesculus is Aesculus parviflora (alright its common name is bottlebrush buckeye-so connecting this plant to the year of the horse is a stretch) and it is a wonderful, summer-flowering shrub that forms a large mounding colony.  It is quite showy in bloom or in fall color.

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Feeding birds

Bobbee™ bayberry (Myrica pensylanica ‘Bobzam’)

A recent article in Audubon Magazine written by Susan J. Tweit (January-February 2013) highlights the importance of planting native shrubs with high fat berries to support our overwintering native songbirds.  Consider the black-capped chickadee, one of the most common North American wintering birds.  They lose heat quickly because they have a large surface area for their size.  They have to feed all day on foods rich in antioxidants and fats.  Then they spend the night crammed into tiny cavities shivering and burning the day’s fuel.

You can help chickadees and many other birds by planting native shrubs and trees with high fat berries. Choose native plants because birds recognize them easily and have to spend less energy foraging. Another benefit of choosing native shrubs is they will support native insects and provide food for baby birds in the spring.

A study conducted at the University of Rhode Island looked at the amount of fat stored in different types of berries.  They found the best berry for fat content was our native bayberry, Myrica pensylvanica, with berries that are half fat! Northern bayberry is a large, semi-evergreen shrub that can get rangy with age.  It makes a great plant for the back of the shrub border of in a naturalized setting.  If you want a more refined selection for a small garden, consider planting Bobbee™ bayberry (Myrica pensylanica ‘Bobzam’).  This cultivar will stay compact, but still provide lots of high fat fruit for the birds.


Plant % Fat
Northern bayberry (Morella [Myrica] pensylvanica)  50.3%
Southern arrowwood (Viburnum dentatum)  41.3%
Gray dogwood (Cornus racemosa)  39.9%
Northern spicebush (Lindera benzoin)  33.2%
American burningbush (Euonymus atropurpurea)  31.2%
Virginia creeper (Parthenocissus quinquefolia)  23.6%

Source: Designing Gardens with Flora of the American East, 2010, by Carolyn Summers 

Some other plants recommended for winter fruit include:

 Wax myrtle (Myrica cerifera) – Smaller bayberry that grows well in the coastal plain, especially at the Delaware beaches.

Southern arrowwood (Viburnum dentatum)Prefers sun to partial shade, moist, acidic soil; foliage rich burgundy in fall; important for native bees and butterflies as well as birds.

American beautyberry (Callicarpa americana) – Likes light shade and will grow in the hottest areas; moist soils; gorgeous purple berries; deer love to browse

Common hackberry (Celtis occidentalis) – Drought-tolerant, craggy tree with knobby bark; fruits eaten by many bird species; attracts butterflies and moths.

Staghorn sumac (Rhus typhina) –Large rangy shrub for big natural areas, leaves turn brilliant scarlet and orange in the fall and berries are high in vitamin C.

Smooth sumac (Rhus copallina) – A little smaller shrub with great red fall color with berries high in vitamin C.

Aromatic sumac (Rhus aromatica) – This sumac is lower growing and has a cultivar, ‘Gro Low’ that makes a great groundcover.

Winterberry holly (Ilex verticillata) – Many cultivars of this popular deciduous holly have large, red fruit (or orange) that can last well into the winter.

Depending where you live and the bird populations present, you may find these shrubs are stripped of their fruit well before they would help our overwintering birds.  In that case, you are helping the fall migrators.  But, the more people who plant native shrubs, the more food we’ll be providing and that can’t do anything but help those birds we love to watch!

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