Garden Clippings 2019 Vol. 38:2

A monthly e-newsletter from UMass Extension, published March to October, for home gardeners.

To read the articles in each section of the newsletter, click on the section headings below to expand the content:

Tips of the Month

April is the Month to.....

• Fertilize houseplants. As days grow brighter and longer and new growth begins, houseplants need to be fertilized more often. Foliage plants require relatively higher nitrogen fertilizer, while blooming plants require fertilizer that is higher in phosphorus. Apply fertilizer according to label directions.

• Prune summer and fall flowering shrubs. Early April is good a good time to prune summer flowering shrubs such panicle hydrangea, butterfly bush, buttonbush, summersweet clethra, sweetspire, and summer flowering spirea. These shrubs form their flower buds on the current season’s stem growth. Pruning these in winter or early spring leads to vigorous stem growth in spring and summer that contains buds that will flower in summer and early fall. Plants like big leaf hydrangea, which blooms on last yera's old wood, should be pruned after flowering, with only the dead stems removed now.

• Prepare garden soil for planting. Do not work your soil when it is wet. Tilling or digging when the soil is wet will cause it to dry into hard clods, so wait to prepare soil when it is dry enough. To test if your soil is dry enough, take a handful of soil and squeeze it. If the soil crumbles easily when you open your hand, it is ready to be tilled.  If it does not crumble or drips water, it is too wet. Allow the soil to dry for a few more days and test again before digging.

• Plant cold tolerant flowers. Pansies and other cold tolerant flowers such as petunia and snapdragon can be planted in April. As these plants become available at local garden centers, prepare your gardens for planting. Plant these plants where they will receive full sun, although some pansies may tolerate partial shade. Water plants thoroughly after planting and mulch lightly with an organic mulch if possible.

• Sow seeds of cool season crops in the field. Seeds of leafy greens such as lettuce, chard, kale, or arugula and roots crops such as carrot, radish, beet and turnips can be planted in the field in April. Plant the seeds as soon as the ground can be worked. You can also set out transplants, which are preferred for leafy vegetables such as kale and chard as they establish faster and mature early. Cool season crops such as spinach, beets, radish, carrots and lettuce are sown thickly in rows and thinned later to the desired spacing to allow them to develop properly. Root crops such as carrots, beets, and radishes should be thinned to a 2-inch spacing to allow the roots to develop properly. They can be thinned as soon as they reach small edible size. 

• Divide fall blooming perennials. Early spring when new growth is emerging is a good time to divide fall blooming perennials. In early spring, the weather is cool and there is usually adequate moisture in the soil. Roots have a lot of stored energy that will help the divisions recover from being cut apart and replanted. The new emerging shoots are likely to suffer less damage than fully developed growth and will also lose less water through evapotranspiration. Spring divisions also have the entire season to recover from the stress of division. Start by digging around the plant and then lift the entire clump out of the ground. Then, using a spade or sharp knife, cut the clump up to separate pieces. Discard the old, dead center and trim off any damaged roots. Keep the divisions moist and shaded while you prepare the new planting site. After replanting, keep them well watered.

• Start seeds of warm season plants indoors. Seeds of warm season plants such as tomatoes, cucumbers, eggplants, peppers, marigolds and zinnias can be started indoors in early April for transplanting later to the garden when it gets warmer. Starting your vegetable seeds early will give your garden a jumpstart on spring by having plants ready when you want to transplant. When selecting vegetable varieties, check for the number of days needed to harvest. Make sure you follow seed packet or catalog instructions, as each species has its own requirements. Make sure you have indirect but bright light around all plants. The more light, the better - up to 16 hours a day. Use cool white spectrum fluorescent fixtures or grow lights suspended above the plants and make sure you move the lights up as plants grow. If you don’t have grow-lights, place your plants on a south facing window, but make sure to rotate the containers often to get sturdy, uniform straight plants. Providing bottom heat speeds up germination and produces healthier roots and plants, and can help prevent “damping off” disease that causes the death of tiny seedlings. Electric heating mats specifically for seed starting are available from many garden centers.

• Rake lawn to remove dead grass and other debris. To facilitate quicker regrowth, rake the turf lightly with a leaf rake. Do not use a garden rake as it will damage the turf. Raking will remove dead and blighted blades and other debris and will facilitate recovery from snow mold and promote quicker regrowth. 

• Reseed your lawn. If you have areas on your lawn that were damaged during the winter, late April is a good time to reseed those areas once soil temperatures have reached at least 50 degrees F. It is safe to apply starter fertilizer that contains nitrogen (N) and phosphorus (P) at the time of reseeding. However, it is important to do a soil test before you apply any nutrients so that you apply according to the rates recommended by the soil test. A starter fertilizer at seeding is beneficial for young turf seedling establishment. Keep the seeded area moist throughout establishment. Water lightly several times a day and avoid runoff. A mulch cover will help keep the area moist and reduce watering frequency. Avoid applying herbicides during the establishment period (spring), as this may cause injury to the new plants. For info on getting a soil test from the UMass Oil and Plant Nutrient Testing Lab, go to soiltest.umass.edu.

• Plant a tree in celebration of Arbor Day on April 26. Arbor Day is an annual observance that celebrates the role of trees in our lives and promotes tree planting and care. Bare root trees should be planted before new top growth begins. Balled and burlapped and containerized trees can be planted later in the spring.

Geoffrey Njue, UMass Extension Sustainable Landscapes Specialist

Timely Topics

Asparagus - Both Ancient and Modern

Quick quiz: What is the spring vegetable that spans the ages — grown in ancient times and eaten by Julius Caesar yet showing promise for a future space colony, shown to be tough enough to tolerate Martian soil according to NASA? Need a few more clues? This workhorse is loaded with vitamin K and folate, and may help to reinforce the walls of blood vessels and relieve hangovers. Still wondering? It’s an easy-to-grow perennial that puts a smile of the face of many gardeners, yet makes them turn pale when they see the pricey bundles of it sold at grocery stores. Yes, you’ve guessed it — good old asparagus!

Planting
Asparagus is a perennial that, with proper maintenance, can remain productive for up to 30 years and, since it does require a bit of a workout to install, proper site selection is important—you don’t want to be disturbing and moving the bed a few years down the road. 

Choose a location with good drainage and full sun (at least 6 hours) that has not been planted with asparagus previously (as fungal diseases may persist in soil). Have the soil tested—asparagus does not grow well in acid soils; if test results indicate low pH, amend the area with limestone according to test recommendations to raise soil pH to around 6.5-7.5. For info on getting a soil test from the UMass Oil and Plant Nutrient Testing Lab, go to soiltest.umass.edu.

Asparagus can be started from seed, but is easier to establish from one-year-old bareroot plants known as crowns (each crown appears as a short section of stem with attached roots and has been grown from seed). Buy from a reliable nursery supplier (conservation district plant sales can be an affordable option for purchasing crowns). Select cultivars such as ‘Jersey Supreme’, ‘Jersey Giant’, ‘Jersey Knight’, ‘Millenium’, or the purple cultivar ‘Purple Passion’, which are resistant to or tolerant of major asparagus diseases — rust and Fusarium crown and root rot.   

Although asparagus can survive in barren soils from Mars, you’ll want to give your plants the best start by spreading and working in a several inches of organic matter — compost, leaf mold, or aged manure — as well as any general purpose (10-10-10) or equivalent natural fertilizer as recommended by the soil test.  

Once soil amendments are worked in, stretch your back, because you’ll be digging a trench — approximately 12 inches wide by 6 to 8 inches deep for the new arrivals (dig slightly deeper in sandy soil, shallower in heavy soil). Place crowns in the bottom of the trench, spaced about 12 inches apart, with their roots spread out. Cover the plants with 2 inches of soil and water thoroughly. As the season progresses and shoots continue to grow upward, you’ll want to backfill the soil a few inches at a time (avoid covering asparagus foliage) until the trench is filled level with surrounding ground. A single trench of asparagus should be kept about 3 feet from other crops, and if you are planting more than a single trench, space trenches 4 feet about from one another to give growing asparagus roots plenty of room to spread. 

Maintenance
During the first year, keep the asparagus bed deeply watered (8 to 12 inches deep) once a week; asparagus’s extensive root system makes it fairly drought tolerant after it’s established, so frequent watering in subsequent years is usually not necessary. Keep asparagus beds weeded to reduce competition for water and nutrients, and once the trench has been fully backfilled, use straw or shredded leaf mulch around plants as a long-term means of keeping weeds at bay.  

Fertilize asparagus in early spring (before spears emerge) by working in a 1-inch layer of compost or aged manure, or apply 10-10-10 (or a natural fertilizer equivalent) according to label directions. Make a post-harvest (third growing season and beyond) feeding with a high-nitrogen fertilizer or several inches of aged manure to boost plant growth throughout the rest of the growing season and safeguard the following year’s crop.   

If you’ve planted disease-tolerant cultivars, your main concern will be pest control. One culprit to keep an eye out for is common asparagus beetle, ¼ in length, and blue-black in color with 6 cream square-ish spots on its back. It feeds on the growing spears, and affected spears tend to turn brown and bend over at the tip. Monitor plants regularly: rub off any clusters of dark brown eggs you find attached to spears, and handpick larvae and adults to drop in a container of soapy water. You may also find adults of the spotted asparagus beetle, which is red-orange with 12 black spots. Their damage can be problematic, but they are not as destructive as the common asparagus beetle.

Once the harvest season is over (after about 6 weeks, when emerging spears are skinny), allow remaining spears to grow tall and produce their fernlike foliage. Cut down the stalks to ground level after they’ve been frost-killed, and remove them from the garden to prevent any lingering pests or disease-causing organisms from overwintering. This is also a good time to test soil pH and adjust with lime to asparagus’s preferred range if necessary.  

Harvesting
As tempting as it may be, refrain from harvesting asparagus spears in the first and preferably second years. This will allow plants to build up a robust root system to support long-term production. However, if you’re finding it hard to wait, take note: research reported by Purdue University suggests that a couple of weeks of judicious harvesting in the second year can actually stimulate bud production and result in better crop yields in later years.

Beginning in the third growing season, harvest spears that are 6 to 8 inches long and thicker than a pencil every few days over a 2- to 3-week period. Subsequent years’ harvests can gradually increase up to a period of up to 6 weeks, as long as plants continue to produce adequately-sized spears.  

No special equipment is needed to harvest asparagus—simply snap off spears just above ground level. Conveniently, asparagus tends to snap at a spear’s transition point from tender to tough. Asparagus is best eaten soon after harvest as it loses its sugar content quickly, but the spears will keep in a plastic bag in the refrigerator for up to a week while you harvest enough for a meal.  

Resources

• Kujawski, Ron and Jennifer. Week-by-Week Vegetable Gardener’s Handbook. Storey Publishing, North Adams, MA.
• Lerner, B. Rosie. Purdue University Cooperative Extension Service Fact Sheet: Growing asparagus in the home garden. Available online at https://ag.purdue.edu/hla 
• Rupp, Rebecca. How Carrots Won The Trojan War. Storey Publishing, North Adams, MA.
• Tufts University Health and Nutrition Newsletter. Nutritious asparagus can put a spring in your step. Available online at https://www.nutritionletter.tufts.edu
• University of Massachusetts Home Lawn & Garden Fact Sheets. Asparagus-growing tips. Available online at https://ag.umass.edu/resources/home-lawn-garden

Jeninifer Kujawski, Horticulturist

News for Gardeners

Winter Annuals: An Often Forgotten Weed Life Cycle

Weeds with an annual life cycle reproduce by seed and complete their life cycle in one year. The annual life cycle is further divided into summer annual and winter annual weeds.

Summer annual weeds germinate in spring or early summer, grow vegetatively, flower, produce seed and senesce (wither and die) in late summer or fall. Examples of summer annual weeds include crabgrass, yellow foxtail, goosegrass, barnyardgrass, ragweed, purslane, spotted spurge, pigweed, lambsquarter, carpetweed and prostrate knotweed. 

Winter annual weeds germinate in late summer and fall. They grow vegetatively and go dormant with the arrival of cold weather. As the weather warms in the spring, they continue to grow vegetatively then switch to their reproductive phrase when they flower and produce seed. After flowering, they senesce with the onset of hot weather.

Winter annual weeds can be just as problematic and troublesome as summer annual weeds, as they are present from late summer/fall to late spring/early summer. Their nickname, the “forgotten weed life cycle”, is appropriate as they occur in lawns, vegetable gardens and ornamental landscapes at a time when gardeners and landscapers may have let their guard down. Below is a table of some of the most common winter annual weeds.

Common winter annual weeds of lawn, vegetable garden and landscape
Note: Species decription and photos can be found in the UMass Extension Weed Herbarium at www.umassweeds.org

bluegrass, annual - Poa annua
bittercress, hairy - Cardamine hirsuta
chickweed, common - Stellaria media
chickweed, sticky - Cerastium viscosum
deadnettle, red - Lamium purpureum
fleabane, annual - Erigeron annuus
henbit - Lamium amplexicaule
horseweed - Conyza canadensis
knawel - Scleranthus annuus
mouse-ear cress - Arabidopsis thaliana
pepperweed, Virginia - Lepidium virginicum    
pineappleweed - Matricaria matricariodes
shepherd’s-purse - Capsella bursa-pastoris
speedwell, corn - Veronica arvensis
speedwell, purslane - Veronica peregrina
thymeleaf sandwort - Arenaria serpyllifolia
whitlowgrass, spring - Draba verna

Management suggestions for winter annual weeds

Lawns:

1. Use cultural practices (mowing, fertilitization and liming) to provide optimal growing conditions for cool-season lawn grasses. Overseeding of thin turf should be done to improve lawn density. A healthy and dense lawn is the first step in an attempt to out compete winter annual weeds.
2. Since winter annual weeds will senesce with hot weather, the use of an herbicide is rarely warranted.

Vegetable gardens:

1. Winter annual weeds will appear in a vegetable garden after the growing season is over, so will not impact vegetable crops. Winter annual weeds present with fall crops will have little or no impact.
2. The use of a cover crop (winter rye or oats) will deter winter annual weeds. The goal is to out compete winter annual weeds and prevent them from flowering and producing seed.
3. Spring cultivation (hoeing or rototilling) will kill winter annual weeds and prevent seed production.

Ornamental landscapes:    

1. Landscapes with sizable populations of winter annual weeds should be mulched in late summer before the seeds of winter annual weeds germinate.
2. In the spring, small winter annual weeds that might exist can be smothered with a fresh layer of mulch.
    

Randy Prostak, UMass Extension Weed Specialist

Trouble Maker of the Month

Cedar-Quince Rust

Cedar-Quince rust is one of many rust diseases in the landscape caused by the fungus Gymnosporangium. Like all species in this genus, G. clavipes attacks redcedar/juniper (Juniperus) and rosaceous hosts, particularly serviceberry (Amelanchier), quince (Cydonia) and hawthorn (Crataegus). In late April to early May, the signs of the disease will become visible on infected Juniperus in the landscape. Red-colored pads of fungal tissue will swell from infected stems and branches and once they become wet, they turn orange and gelatinous. These spores disperse to infect rosaceous hosts. On serviceberry, quince and hawthorn, stem distortion and cankering can occur, in addition to a fruit blight and leaf spots. On shrub serviceberries, significant canopy dieback can occur as a result of the stem cankering. Signs of the disease on rosaceous trees and shrubs do not appear until mid-summer. Most Juniperus are largely unaffected by the disease, but often serve as a perennial source of the pathogen in the landscape. Therefore, early season scouting should be performed to confirm the presence of the pathogen. See UMass Extension's Cedar-Quince Rust fact sheet at http://ag.umass.edu/landscape/fact-sheets/cedar-quince-rust for more information and photos.

Nicholas J. Brazee, UMass Extension Plant Pathologist

Plant of the Month

Abeliophyllum distichum, White Forsythia

All winter long, small black buds adorn the tips of slender, arching, leafless branches and stand in stark contrast to the pure white snow of winter. The arching stems cross over one another as if fighting for prominence at the top of the 4’-5’ tall framework of this deciduous shrub. In central Massachusetts, the air warms sufficiently around the middle of April, and the black buds begin to swell, eventually opening to reveal four-petaled white flowers which dangle elegantly in short axillary racemes along each branch. The flowers follow the same shape and form of their cousin, the common forsythia, though they are a bit smaller and clean white rather than garish yellow.  

White forsythia is not a true forsythia but, like Forsythia x intermedia, it is a member of the Oleaceae or olive family, a clan which also includes Lilacs (Syringa sp.), Privet (Ligustrum sp.), Fringetree (Chionanthus sp.) and the tender fragrant olive (Osmanthus sp.). Abeliophyllum is a monotypic genus containing just A. distichum. Its name is derived from ‘abelio’, referring to the genus Abelia, and ‘phyllum’ for leaf, together combining to indicate the resemblance of the leaves to those of Abelia. The specific epithet ‘distichum’ also refers to the leaves and indicates the paired, or two-ranked, arrangement of leaves. The leaves are simple, ovate and 2-3” long. They remain deep green in summer and rarely offer any fall color, though sometimes will show hints of red, yellow and burgundy before dropping. Like many of its cousins, it is pest and disease resistant. 

White forsythia flowers are about 1/3 of an inch across, though a quirky cross-pollination strategy has resulted in two types of flowers occuring on plants within this genus. The flowers types are very similar to one another, but differentiated by the placement of the reproductive parts and by a small difference in size. Those flowers with the style or female part extending beyond the male, pollen bearing stamens are called pin flowers. Those with the stamens forward – extending past the female style - are called thrum flowers. The placement of the parts makes pollination more likely when bees visit both types of flowers, transferring pollen from one plant to the other. This quirky occurrence, called heterostyly, also occurs in forsythia and jasmine, both members of the Oleaceae family, as well as in about 27 other families of plants. In Abeliophyllum, the thrum flowers are a bit larger than the pin flowers, but not so much so that you are likely to notice.    

In full sun or part shade, and given good growing conditions, the flowers will be borne in abundance. If temperatures remain moderate in the spring, they will provide a floral show for 10-15 days from mid to late April. As the flowers age, they gently fade to pink; some variants tend towards pink so frequently that they are often sold under the cultivar name ‘Roseum’ or as part of the Roseum Group. A sweet fragrance, likened to almond, accompanies the bloom, making this a lovely choice for a protected spot where the fragrance can be captured and enjoyed. Planting in front of a dark backdrop like an evergreen tree or shrub, or a dark structure, creates a pleasing contrast with the pristine flowers. Abeliophyllum will tolerate short periods of drought, but is best grown in a moist but well-drained garden soil. It is not particular as to pH, though would not perform well at extremely low or high pH conditions. It is stunning combined with the blue flowers of Siberian squill (Scilla siberica), glory of the snow (Chionodoxa forbesii), and windflowers (Anemone blanda ‘Blue Star’) with whom its bloom overlaps. Other early blooming companions include Iris ‘Harmony’, hellebores (Helleborus X hybridus), hyacinths (Hyacinthus orientalis), and Pigsqueak (Bergenia cordifolia). This unusual shrub is hardy to zone 5 (-10 to -20 degrees), though in fickle springs flowers may sustain damage from late frosts, particularly if they have gotten off to an early start. 

Though this is an undemanding shrub, one finds it variously described as a heap of twigs, a messy form, straggly or unkempt. These descriptions may well fit an untended plant that’s been left to its own devices, but a more acceptable and tidy shrub is easily formed with a bit of smart pruning. Shaping cuts and rejuvenation every few years will encourage new growth and a fuller, tidier plant as well as more prolific flowering. Prune immediately after flowering and shorten any excessively long stems which arch and root. It is altogether smaller and more manageable than its robust cousin, Forsythia x intermedia and deserves a place in the modern, often smaller garden. It can be easily propagated by layering a stem – that is, bending and pinning a stem to the ground, ensuring contact with soil. Roots will form in the axils and along the stem and the new plant can be separated from the parent plant once it’s well established. Semi-hard stem cutting can also be taken in summer.  

Growing this plant not only provides human enjoyment in a season where little else is making a show, it also helps pollinators in the very early shoulder of spring, and since this plant is so rare that it verges on extinction in its native range of central Korea (now found in only seven sites), including it in our landscapes can help ensure its future. 

 

 

 

 

 

Joann Vieira, Horticulturist