Powdery Mildew

By Norma Owlcarver, Master Gardener

Powdery mildew is a common fungal disease of plants in our area that occurs this time of year. It’s named for the grayish white powder consisting of fungus strands on the leaves of the plant. The fungus uses the host plant for its food supply by sending root-like structures into the leaves and stems.
Powdery mildew likes the humid conditions we experience in New England on warm days and cool nights. Some particularly sensitive plants are apples, roses, grapes, peas, potatoes, phlox, squash and zinnias, though there are many more. It’s common for it to start in crowded plantings where air circulation is poor and in damp, shaded areas.

If you’ve had powdery mildew on your plants in previous years, it’s likely to return this year. There are, however, some practices you can institute that can reduce or even prevent future infestations. Additionally, many resistant varieties have been developed. For information and to learn what some of these plants are, click on the website links at the end of this article. You may also want to check for resistant varieties at your favorite garden center.

Injury due to powdery mildews is often of minor consequence to healthy plants, although it can become unsightly. If damage occurs, it may include the stunting of leaves, buds, growing tips and fruit. It can cause the death of invaded tissue on some plants, i.e., begonias. Leaves can yellow and cause the death of tissue, which can produce premature leaf drop. When plants are infected, nutrients are removed from them by the fungus. This may cause the loss of vigor in the plant and produce a general decline in growth. The taste of squashes and some other vegetables may also change.

Should you wake up to those powdery looking leaves in your garden this year, consider the following cultural practices to reduce the potential of it spreading further and, perhaps, eliminating it next year

1. As much as possible, when planting flowers or vegetables that you know are prone to powdery mildew, plant in an area with full sunlight and where the soil drains well.

2. When putting in new plants assure you are not crowding them.

3. If you have plants that are already infected, you can increase the air circulation by selectively pruning overcrowded plant material on the plant and between plants. This will help reduce relative humidity and reduce the chance of further infection.

4. Avoid overhead watering to help reduce the relative humidity, or water in the early morning to let the tissue dry as soon as possible.

5. Don’t make late-summer applications of nitrogen fertilizer. This will limit the plant’s production of succulent tissue, which is more vulnerable to infection. Powdery mildew tends to increase in high nitrogen soils so you may want to consider using an organic fertilizer or a slow release fertilizer.

6. When the growing season is over and you are closing your garden for the season, remove and destroy all infected plant parts (leaves, etc.). This will decrease the ability of the fungus to survive the winter. Do not compost the infected plant debris, as the spores (seeds) can overwinter and temperatures often are not hot enough to kill the fungus.

7. Disinfect the tools you use to prune infected plants and all your other garden tools that may have contacted the diseased plant, in a bleach and water solution.

If you decide to treat plants infected with powdery mildew, researchers at the University of Rhode Island (URI) have confirmed that a combination of 1 tablespoon baking soda plus 2.5 tablespoons of horticultural oil in 1 gallon of water is effective against powdery mildew on roses. Other New England University Extension web sites suggest this combination for other crops, but URI states this is still experimental.

Sulfur products have been used to manage powdery mildew for decades, but it is only effective when applied before disease symptoms appear. If you use this method, use wetable sulfur with a sticker, as it will work best. Read all of the directions on the product. Start applications right before the mildew normally appears. As a precaution, before starting applications to the entire plant, apply the solution to a small test area to assure leaf burn will not occur. If the test is successful, apply the product carefully after each rain until the mildew is under control. Make sure to include the bottom of leaves in your applications.

As stated above, consider disease-resistant varieties before you plant, but keep in mind that resistant does not mean immune. Cornell University’s Vegetable MD Site has numerous listings of disease resistant vegetables that are available. The site address is


If you know you are already growing plants that are prone to downy mildew, which is different from powdery mildew and occurs under different environmental conditions, but is hard on many types of roses, as well as other plants, follow the 2009 mildew forecast recommend by Cornell and developed by North Carolina State University (UNCSU). UNCSU is reportedly working to expand this forecast tool to include other mildews. The forecast and alerts can be followed for the entire U.S. or just MASS. The forecasting address is


At this site you will also find alerts of when the first signs of downy mildew are first spotted in all of the 50 states.

In summary, whether you manage the plants you have to prevent and/or eliminate powdery mildew or choose to plant with resistant varieties, your first line of defense is to follow good cultural practices in your garden and with your lawn.

henry hudson rose.jpg

Roses From the North
by John Barry, Master Gardener

Thinking about growing roses? How about roses that are winter hardy, disease resistant, have a full range of colors, repeat their  blooms, are fragrant, can be used as hedges, as  climbers or stay compact. Also, since they are so tough and independent they would prefer not to be sprayed.

Roses like this do exist and come from Canada. These explorer roses generally fall into two categories: either Rosa rugosa hybrids or hybrids that use Rosa kordesii. The Rosa kordesii crosses can grow into very vigorous shrubs and can be used as climbers. These roses are listed as the "Canadian explorer series". They were so named by their breeders in the hope that they would bring the same toughness and hardiness as their namesakes. Here are some of these explorers that I have grown with some success:

  • Martin Forbisher- 5x4, blush pink(strawberry), semi-double, clean foliage. Has an open habit but does not finish it's blooms well. Probably my favorite.
  • Jens Munk-5x5 ,a Rugosa hybrid, medium pink, semi-double, very fragrant.
  • Henry Hudson-- 4x3, white ,semi-double, compact plant, does not finish well, fragrant. Unfortunately the beetles love this guy.
  • William Baffin--bright pink, semi-double, very vigorous and hardy. Needs to be fed well to perform at his best. Can be used as a climber.
  • Henry Kelsey--Kordesii hybrid. Dark red semi-double flowers. A climber. Good bloomer.

There are many more of these explorers which I’m sure will perform just as well as the ones named here. Aside from the Japanese beetles, these roses come as close to perfect as a  rose grower can ask for. So if you are thinking of roses try a couple of these guys. If for nothing else the names are cool.

Click here for the companion to Roses from the North Coffee for Roses...and 70 Other Misleading Myths About Backyard Gardening


By Edna Colcord, Master Gardener     

This is the year that I shall get a rhubarb patch. Finally I have a spot selected where this perennial might flourish and not get eaten by the sheep. The sheep do not seem to be deterred by the oxalic acid in the leaves even though they are poisonous. The leaves can be soaked to make a bleaching agent. People should never eat them. The stalks do not contain the compound.

Rhubarb needs good sun with some protection from drying-out; a rich, well-drained soil, and to be placed where it can grow undisturbed for years and yet be close enough for the gardener to gather the nutritious stalks. Rhubarb is a storehouse of essential minerals, and while tart, there is nothing better than this vegetable to make a pie, sauce or conserve for balancing the “bad” sugar with such a high source of calcium and potassium. Its roughage has long made it a staple of “spring tonic” cleansing. A stalk lightly salted is one of the memories associated with the joys of the spring season, which every child should try. It freezes well for cooking.

Bolting, or the perennial’s need to flower, is a problem that can be attacked by simply removing the flower stalks as they start to come. After a while the plant decides that it will stop the effort but it seems that warm soil puts it in reproductive mode. Newer cultivars like Canada Red and Valentine tend to bolt less than some of the older ones like Victoria and MacDonald. Often pots sold do not identify what cultivar it is and it is hard to judge if you will get a large- or slim-stalked variety. Rhubarb grown from seed will not necessarily be like the parent and may actually end up as an errant child with none of the characteristics you want. Here in NE there is a preference for red stalks, but they can be red, pink or green. There is little difference in flavor. Early production and thin skin are also two characteristics to consider.

The idea is to find someone you know with the plant that has the color, stalk and hardiness you want and beg or trade for a good slice of the original plant with its roots intact in its ball of soil. When ready to plant, a good hole with compost and proper drainage should be waiting. Plants are influenced by their environment and they still may show some variations from the original. Large plants should be treated like all perennials, dividing the crowns every 4-5 years, but they can go much longer. When harvesting, enough leaves should be left for the plant to store carbohydrates for the next season. It is a good idea not to take more than 1/3 and to stop harvesting by the 4th of July. Some people cut and others pull. There are spore-bearing disease agents that are more easily introduced by cuts. A layer of peat moss is reported to discourage disease. Rhubarb is a heavy feeder. The soil must be kept healthy.

I will have to beg or buy this year’s crop and may only have a little produced next year but I can already anticipate a plot that will produce for years to come. I imagine introducing my baby granddaughter to the delights of a freshly pulled stalk, leaves carefully removed, and a dash of salt which will rival any jarred pickle for sheer sour joy.

Seed Starting - It's That Time Again

By Debra Hayes, Master Gardener

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There are many advantages to starting your own seeds. Everyone has their own reasons, not the least being that watching those green babies grow helps many of us get through a long New England winter. Some of the many advantages of nurturing your own plants from seed include less expense, you can choose which varieties you want and choose from a much broader selection. You can grow your own seedlings organically, and have healthier and more nutritious food for you and your family. Starting seeds yourself also minimizes the chance of introducing soil-borne diseases to your garden, and your individual, loving attention will yield healthier and higher quality plants. You can also time planting to your own schedule and needs. You can start your tomatoes extra early for the first ripe tomatoes in the neighborhood, and start broccoli for a fall planting.

It's always best to start with fresh, high quality seeds. Mail order seed catalogs and seed packets can provide important information. First look for hardiness for your area and days to maturity, to make sure you have enough growing days. You'll also want to get information about each seed's germinating needs. Do they need light or dark, cool or warm temperatures? Some seeds need soaking, some stratification to break dormancy, and some need to be scarified. You'll also need to know how many weeks before planting outside sowing is advised, usually between four to ten weeks.


There are only two requirements for containers to start your seedlings. They must be scrupulously clean, and afford proper drainage. There are two main styles, seed trays or flats, and individual seed containers. You can buy them new, clean used ones, or recycle empty yogurt, milk and similar containers. A solution of 1/8 cup bleach to 2 gallons water can be used to rinse used or recycled containers after a soap and water cleaning to prevent disease.

Growing Medium
No one perfect medium exists. Seedlings thrive in a moist, spongy growing medium. "Soil-less" mediums work really well here, and usually contain a blend of vermiculite, sphagnum moss and/or peat, and Perlite. They work better than garden or potting soil, as they retain moisture, provide good aeration, and reduce pest and disease problems. You can mix your own using 1/3 to l/2 sphagnum moss or peat, and the remainder vermiculite or Perlite. Ready-made mixtures like Pro-Mix work great and are readily available. Whatever you use, it must be sterile.

In order for a seed to germinate, it must be mature and viable, and receive the proper combination of moisture, temperature, light, and air. Most annuals, vegetables and herb seeds germinate easily. However, there are some that need special attention. Perennial seeds, in general, need more attention than others. Some seeds may need either complete darkness (Calendula, Bachelor Buttons, Larkspur) or constant light (Snapdragon, Petunia, Yarrow) to germinate. Some need to be soaked (Parsley, Asparagus, Morning Glory) because their seed coats are very hard, preventing moisture from getting through. Some seeds may contain a chemical substance that inhibits germination. Soaking is then needed.

Some seeds need stratification, a cold treatment, before sowing (such as Echinacea, Lavender and Columbine). Some seeds need scarification (Lupines, Sweet Peas), by nicking or filing, before sowing. Some seeds need cool temperatures to germinate. Examples include Rosemary, Lettuce, California Poppy. Some seeds do not transplant well and should be planted in peat pots, examples being Nasturtium, Dill, and Poppy. This information is usually provided in the seed catalog, on the seed packet, or in a good gardening book.

Very fine seeds should not be covered with medium, but merely pressed into the surface. All other seeds, except those that need light to germinate, should be covered with one to two times their thickness, then watered carefully. To provide consistent moisture, some gardeners cover flats with clear plastic, which should be removed as soon as germination occurs. Make sure you label each flat, row, or container, and place in a warm area. Most seeds germinate best at about 75 degrees unless otherwise stated. Check your seeds daily for germination and soil moisture. Soil should be kept moist, not wet. Use tepid or room-temperature water.

Care After Germination

Seedlings prefer a temperature around 60 degrees F. Sturdier plants will be produced at this moderate temperature. Some recommend a 5 to 10 degree temperature at night. Too much warmth can produce tall, weak, spindly plants. 

As soon as seedlings have sprouted, they should be placed in a bright location, but not strong sunlight. A South facing window will do, but it may not be ideal, so try turning your plants daily and insulating the windows at night. Plants may become spindly from too high of a heat-to-light ratio, or stressed by the drastic drop in temperatures at night.

If you aren't lucky enough to have a greenhouse, fluorescent lights work very well. You can use four foot shop lights using regular (cool white or warm) or special grow light tubes. Special grow lights are necessary only when you wish to start plants for indoor flowering and fruiting. Otherwise, use one cool and one warm, or all cool, per light fixture. Avoid using all warm as this could make for spindly plants. Lights should be placed 3 to 4 inches above the seedlings. As the plants grow, maintain the 3 to 4 inch distance between plant and light. Lights should remain on for 12 to 15 hours a day. Timers are well suited for this.

If you're planning to start small, with just a few trays, you can create a light stand with a wooden plank with bricks holding it up. Attach a light fixture to the plank. You will need to be able to either lower and raise the fixture, or raise and lower the plants.

My first made stand used 2 x 4s and plywood shelves. It held 12 four-foot lights on chains. Now I'm using 4 foot long baker’s racks, which are easy to assemble, and the wire shelves are perfect for attaching the fixtures. You can find them at some used restaurant supply stores, or stores going out of business.

Once seedlings have developed their first set of true leaves (the second two leaves), you'll need to start feeding them. Water them once a week with a fertilizer that you've mixed half strength for roughly two weeks, then gradually increase to full strength. Fish emulsion, seaweed fertilizer, or a mixture of both work well here.

Damping-Off and How to Avoid It
Damping off doesn't give you much warning. The first sign that you have a problem is the total collapse of a few seedlings, green leaves still intact, but the stem has withered away at soil level. Young seedlings are most vulnerable, and once they have been attacked by the damping-off fungus, they can't be revived, as the lifeline between root and stem has been cut off. Prevention is best.

Avoid damping-off by using sterile growing medium only. Also sterilize all containers and tools used in the sowing process. Sow seeds thinly to allow healthy air circulation, and thin to avoid overcrowded containers. Watering seed trays from below is best, but not always possible. Avoid over watering, keep medium moist, but not wet. Maintain good air circulation, and fertilize only after seedlings develop their first set of true leaves. If the problem occurs, immediately remove tray to a more open area. If soil appears too moist, let it dry up a bit. Remove all dead plants and the surrounding plants from the tray.

Seedlings grown from very fine seeds will probably need thinning before they are large enough to transplant. Thin to one plant every one and a half to two inches by snipping off at soil level.


Seedlings not planted in individual pots need to be transplanted when they have developed their first true leaves. Plants that take well to the transplanting process are usually greatly improved by the experience. Fine roots are broken by the transplant process, and as a result, a new, bushier network of feeder roots is formed. Repeated transplanting, three to four times, before planting outside, produces stocky, well rooted plants, but it is not necessary- I'm lucky to be able to do it once!

First prepare your flats or containers you'll be transplanting into. Use a transplanting medium, potting soil mixture, or your own blend, it need not be sterile. Prick out seedlings gently, loosening a small clump from the tray using a small knife, Popsicle stick or similar object.

It is very important that the roots never dry out. Using a pencil as a dibble, make a small planting hole for each seedling. If transplanting to flats, holes should be placed at least two to three inches apart, and at least three inches if they are not likely to be transplanted again before planting outside. If using separate containers or six-packs, put one seedling per container or compartment. Carefully separate individual seedlings from the clump, when possible, each with a clump of soil around the roots. It is better to hold seedlings by their first leaves rather than their easily bruised stem.

Position the plant to be the same level in the soil or slightly deeper than before transplanting. There are exceptions, such as tomatoes, that you can plant all the way up to the true leaves, as roots will grow off the stem. Tamp lightly around each seedling, moisten immediately. It is recommended that you moisten the soil by placing the containers in a shallow dish of tepid water to allow absorption, or mist until thoroughly moistened, using water that has set to room temperature. Water that is straight from the tap can shock the delicate seedlings.

This is the time to start lightly fertilizing with a weak solution of seaweed and/or fish emulsion. Always label the containers with plant variety and the date they can be safely put outside.

Hardening Off
Once the weather has warmed up, it is necessary to harden off your plants. You do this by gradually exposing them to the outdoor weather. One week before transplanting outside, start the process by moving the plants outside into a sheltered, shady area, such as a porch, cold frame, or under a tree. If it gets cold at night, or windy, move them back inside. Gradually increase the amount of sun each day, making sure they are well watered.

Cold Frames
Cold frames are very useful, and are similar to a miniature greenhouse. They can be as simple as just bails of hay and an old window. They are great for starting seeds in early Spring or late Fall. Perfect for hardening off your seedlings, or extending your season by protecting from frost. Southern exposure is a must, with some protection from cold winds, and as close to a 90 degree angle to the sun as possible.

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