Q: We water our garden and lawn with sprinklers. How can we tell how often and how long to water? The grass and the plant leaves are staying green, but I am worried that we may be wasting water by running the sprinklers longer than necessary.
A: The accepted rule is that most plants, whether garden flowers, vegetables, trees, or grass, need an inch of water a week in hot weather to stay green. At the beginning and the end of a growing season less water is necessary because days are shorter and temperatures lower. Once in a while there may even be a rain that contributes to the total, but summer rains are few, and usually of insignificant quantity.
I find that the easiest way to know how much to water is to measure just once the output of each sprinkler and write it down. If the list is kept with the irrigating system or somewhere that it cannot be lost, the measuring job will never have to be done again.
Measure the actual output of water with a flat pan like a cake pan. Set the pan anywhere in the middle of the area to be watered and turn on the sprinkler. After a reasonable length of time, measure the depth of water in the pan with a ruler. It will be easy to figure out how long the sprinkler must run to provide a quarter or a half inch of water.
In addition to the quantity of water provided to plants, the frequency of watering is important. Few garden plants stay healthy in hot weather if they get their whole inch of water once a week. Too many surface roots dry out and die before the next irrigation comes.
On the other hand, plants are not healthy if they are given little sips of water with great frequency. The root systems stay small if the soil is always wet. If the surface dries between watering times, the roots will stretch themselves out to search for moisture. A happy medium in timing results in happy plants.
I choose to water everything twice a week, giving every area half an inch with each irrigation. I check my list to know how long each sprinkler needs to run to put out that amount of water.
Q: What is the perennial that I have seen with a spike of fuzzy pink flowers? The leaves are long and narrow, and all at the bottom. It is blooming right now.
A: You would have seen gayfeather, which started as a wildflower of the prairies and now is commercially available as a garden flower. There are many species, but only one commonly sold for gardens. Look for it on lists as Liatris spicata and sometimes as a variety called 'Kobold,' which is a shorter plant. Liatris plants are sold during spring and summer; the corms from which plants grow are available in spring, and they are how I started my plants.
Some of the other Liatris species are probably less popular in gardens because the flowers are spaced out along the stem, not densely clustered in a club-shaped spike. All Liatris are among the few flower spikes which bloom from the top down. Mine grow to about three feet tall, although I understand that in some places they may grow as tall as six feet. Butterflies love to feed on the flowers and can be seen fluttering around that part of the garden as soon as florets begin to open.
After growing gayfeather for a few years, I rebelled against one more hot pink flower and banished it from my garden. At the same time, though, I discovered that there was a white form which I love. Its white wands have been part of my late summer perennials ever since.
Supposedly the flower spikes of gayfeather can be cut and hung upside down for dried flower bouquets. I have not tried that. I have left a few spikes on the plants to turn brown and ripen. If left in the garden over the winter, some seeds will germinate and add to the plant colony the next year. Leaving all the flower heads to ripen produced more seedlings than I wanted. Letting the plants seed themselves is far easier than collecting seeds and planting them. Home collected or commercially packaged seed needs at least two weeks of cold stratification before it can germinate.
Liatris plants need at least half a day of sun to bloom well. That is not surprising for prairie natives, but it is surprising that they cope very well with poor quality soil. They do not get diseases and are mercifully bug free.
Q: My squash plant has dusty gray patches on the leaves, which I think are called powdery mildew. What can I do?
A: Your diagnosis sounds right. Powdery mildew is a common fungal disease in late summer, and the big leaves of plants in the squash family (including cucumbers) often are infected. As the mildew spreads, large areas of the leaves turn brown, and finally whole leaves die. You can fight the infection in several ways.
First, cut off infected parts of the plant and dispose of them. Do not put them in the compost pile, where the fungus could live to spread in future gardens.
Second, mulch around your plant to keep the soil surface moist. Powdery mildew spreads rapidly when plants are dry. Water your squash plant more often for the same reason. Watering with a spray in the early afternoon is particularly beneficial. At that time of day the mildew spores are flying around, and they cannot stick to wet leaves.
Third, spray the squash leaves with neem oil. That natural fungicide will probably not end the mildew infection, but it will slow the spread. That will allow you to harvest more squash, even though the plant may be sickly.
For future squash plants, look for varieties which are labeled as mildew resistant. There is quite a difference in susceptibility among different squash. Be sure that the squash in future gardens are not crowded among other plants. Good air circulation is a primary weapon in fighting off any destructive fungus.
If you prefer a lawn without dandelions, now is the time to be looking for this year's seedlings. Rosettes of small to medium sized leaves are now appearing among the lawn grass. Cutting dandelions now means that they will not have the rest of the summer to grow and be ready to flower next spring.
For gardeners who still have not tried mulching, garden writer Dan Pearson advocates it in his book Natural Selection: "Where I grew up...mulching was a necessity, for the soil dried as soon as you turned your back, but not before the chickweed had taken you hostage."