Everyone loves the summer, but it is even more special for a gardener as we get to grow the plants we love! Times of excessive heat like we are experiencing now can make things very difficult not only for the gardener, but also for the plants. Although intense heat is detrimental to many of our crops, excessive heat early in the season can make it particularly hard to start a garden.

ML 21 Sprinkler

During heat waves, watering regularly becomes much more important. Photo by mrl2021

At this time of year, most plants do not have a very well-established root system. Many people do not plant their gardens until after Memorial Day here in Connecticut, even though mid-May is generally the last frost free day. Newly transplanted plants cannot handle intense heat – even if you are watering them. They simply do not have the established root system needed and wilt in the hot sun. The top layers of soil dry out rather quickly, and deeper roots are necessary to find the moisture. 

Seed starting can be particularly problematic at this time as well. Remember that seeds need not only proper temperature, but proper moisture. Seeds are generally planted within the first few inches of soil at most. This layer dries out rather quickly, so keeping the seed bed consistently moist during germination is a daunting task. With both transplants and seed starting, I will generally wait until after a heatwave has passed.

There are a number of crops that do not do well in hot summer heat. Most of the Brassicas despise the heat. These crops include cabbage, Brussel sprouts, broccoli, kale, etc. Peas and lettuce also do not like the heat. The best thing to do is keep these plants watered (more on this below), or planted in partial shade. Another option is placing a shade cloth over these plants to reduce the sun and lower the temperature. Some light does pass through, but they are not out in the intense sun.

Some garden victims are our planters, flower pots, and hanging baskets. Any type of container generally dries out rather quickly. They are above ground and many times dark colored. Both contribute to rapid drying out of the soil inside. Sometimes you can buy special soil or add components to the soil to prevent this rapid dry out, but you can expect to give more watering attention to containers during heat waves. Once a day watering may be necessary, though time consuming. Many of the commercial nurseries have automatic watering systems to take care of their stock while it waits to be sold. Containers should be watered until you see water flowing out the bottom. Be careful as severely dried pots will have soil pulled away from the sides and water will flow out the bottom immediately. In this case, a slow hose drip for an extended period of time may help, as will additional soil added to the pot.

ML 6-21 Flower pot

Containers of all kinds are particularly prone to drying out. Photo by mrl2021.

Although we normally think of it as a weed preventer, one of the easiest ways to prevent our soil from drying out is a good layer of mulch. You will need to put on a decent layer because a thin little layer does not do much. I put on at least three inches of mulch or more. People wonder what type of mulch is best, but I say use what you have available. Mulched areas tend to need to be watered less due to the moisture retention so make sure to take this into account when you are watering.

ML 21 Rhubarb

A well-m.ulched rhubarb plant. Photo by mrl2021

Regular water in is essential to keep our crops in good shape. This can be harder to do than you think. One trap I have been caught in in the past was believing the weather forecast. I remember one year where we were supposed to get significant rain each day. I thought, “Why water when it is going to rain?”  Well it did not. The next day it was the same story, and this went on for almost a week. My poor plants were wilting and miserable by this time. It is not good to stress the plants like this. And if you are not paying enough attention, it can be too late to fix! My rule is to water when the plants need it regardless of the forecast (unless 100% rain is predicted). Our plants need about one inch of water per week. Too much can contribute to rot and fungal diseases. Too little and our plants will languish. You can measure the amount of water being put down with a good rain gauge.

ML 21 Rain gauge

One of author’s rain gauges. Photo by mrl2021.

It is best to water in the morning. Evening watering keeps the plants wet and can invite fungal problems, and slugs love the moisture! Watering in the hot mid-day sun can cause water droplets to form on our plants and burn them when the sun’s rays hit. I have found this is particularly problematic with cabbage. In the early morning, before the heat of day, is best. The problem is that many of us go to work at that time! I set the hoses up the night before and then turn on the spigot when I wake up, and turn off before I leave. Another option is using a timer. There are many manual and digital timers out there. I generally get a bit nervous with these as your water must remain “on” for them to work. Should something fail, water will be gushing all over until you come home. I do know many people who use and like them, so I guess I am just being paranoid. 

I am going take this time to remind everyone to get a good soil test. Not only will you be able to dial in your nutrient requirements, but you should be able to find out what type of soil you have.  You will need to adjust your watering based on your soil type. Sandy soils will tend to dry out much quicker than any other type. Clay soils tend to hold water and can become water logged.  Adding humus will improve the quality of both soils.  

My last bit of advice is to not forget about you! Drink water throughout the day when it is hot.  Too many times I have come in feeling great about the work that was done, but not feeling very good physically as I did not drink enough. It is easy to focus on the work and forget about ourselves. Take frequent breaks! Try to minimize the time spent outside at the hottest part of the day (afternoon around 2pm). Try and follow the shade and work on that part of your garden if possible. The early morning and the late evening are generally much cooler, although you won’t have as much time. Wear sunscreen and/or protective hats and clothing. Above all, find a nice comfortable chair placed in the shade and in view of a beautiful flower garden. Add a cup of lemonade or iced tea and you are all set! 

Matt Lisy

With the dog days upon us, getting adequate water to our gardens can be a concern. Water is essential to all life. Plants use it to transport nutrients and to maintain turgor – the cellular pressure that keeps soft tissue from wilting.  Plants absorb water (containing soluble nutrients) through their roots and ultimately release it into the atmosphere as vapor through small pores (stomata) on the undersides of leaves in a process called transpiration. Although invisible, the cumulative volume of water transpired by Earth’s plants is prodigious, producing 10% of the atmosphere’s water vapor. One large oak tree can transpire 40,000 gallons per year. Drought stress occurs as transpiration continues and soil moisture is exhausted.

Wilting muskmelon plant
Photo: Erika Saaku, Iowa State

Transpiration rates increase with:

  1. High temperatures
  2. Low humidity
  3. Wind
  4.  More soil moisture
  5. Larger, thinner leaves

Hydrangea or squash leaves wilt on hot, dry, windy days because the transpiration rate of these large-leafed plants is faster than the plant’s ability to take up available moisture from the soil.

At the other end, if a plant’s root system is compromised or undeveloped, extra care must be taken to ensure survival. The process of digging and transplanting exposes roots to the air, damaging or destroying delicate root hairs. Recovery can be difficult with the additional stress of hot weather. Provide shade and plenty of moisture to allow these essential single-cell structures to regenerate. In some cases, cutting back some of the leaf mass to reduce water requirements is advisable.  Old-fashioned advice for transplanting instructs: “water once a day for a week, once a week for a month and once a month for a year.” A very inexact guide to be sure, but a good reminder that transplants have high water demands at first and need to be weaned gradually over time.

Container-grown plants often have root systems a fraction of the size of an equivalent plant growing in the ground. Regular watering is a must, particularly when  containers are made of porous clay or fiber. Potting mixes are commercially available that contain polymer crystals which can dramatically increase the water-holding capacity of potting soils in containers.

Measuring irrigation output

“Deep and Infrequent”

This mantra of watering advice emphasizes the need to train turf grass and landscape plants to develop deep root systems in search for water. Shallow, frequent watering encourages the growth of roots close to the soil surface, making the plant vulnerable to drought stress.  Shrubs and trees with weak, superficial root systems are also more likely to topple over in a windstorm.

Root growth of turf ceases at soil temperatures of about 70°, so lawns should be encouraged to develop deep root systems during the cool weather of spring and fall. Summer watering of lawns is triage; keeping the patient stable until temperatures drop. Overwatering results in excessive growth and increased risk of fungal disease, while wasting water and fertilizers that can potentially contaminate waterways.

Mulch conserves soil moisture as it suppresses weeds and dresses up the garden.  Organic mulches mimic the natural duff on the forest floor, creating a hospitable environment for microbes, fungi, insects and worms as they perform their function of decomposing organic matter and releasing nutrients.

Managing water in the garden is a skill that gets honed over time, as the gardener develops sharper instincts for plant requirements. Water is also a surprisingly efficient and environmentally sound way of ridding plants of some insect pests such as aphids and spider mites – simply knock them off with a forceful spray from the hose. Regular flooding will discourage ground-dwelling bees and wasps (yellow jackets) from nesting in inconvenient areas.

Water makes the garden more pleasurable for people and animals alike. Bird baths, gurgling fountains, lawn sprinklers for children or ponds with fish and frogs create a richer environment and a cool oasis of refreshment on a hot summer’s day.

Children swinging in sprinkler, 1964
Photo: Museum of History & Industry, Seattle

J. McInnis

Typically if it is January in Connecticut, one’s horticultural proclivities are turned towards indoor plants. I’m thinking this might be the beginning of another atypical year as temperatures in Storrs, CT were in the 50’s today and I had to water some outdoor hardy chrysanthemums under an overhang because they were wilting. These lovely burgundy mums have survived in this spot for almost a decade and they flower profusely each fall so I did not want to lose them. Usually the ground is frozen in mid-January and I throw some snow on them as a winter blanket. Snowfall has been in rather short supply this winter and the little I had covering them from last Saturday’s snowfall had melted quickly as temperatures rose.

In the case of these chrysanthemums, the young basal sprouts were wilting obviously because of a lack of water. I could see and feel the dry soil. Plants need water, just as we do, to grow and survive. Water is necessary for photosynthesis. It moves nutrients and photosynthates throughout the plant, it acts as a coolant and it gives a plant turgor along with many other less obvious but just as important plant functions. One might suppose that limited quantities of either natural precipitation or human supplied water would be the primary reason a plant would wilt. While it is a major one, there are three other situations where wilting could commonly occur – at least when dealing with houseplants.

Overwatering will cause a houseplant to wilt. In fact, I recall seeing somewhere that overwatering was the number one cause of houseplant death. Many houseplant owners like schedules (as a good number of us do) and water accordingly. So, if today is Saturday, it is time to water the houseplants. The problem is, the houseplants may or may not need water. When to water depends on the type and size of plant, the size of the pot, indoor temperatures, exposure to light, and the plant’s growth cycle among other factors. If heat is provided all or in part by a wood or pellet stove and plants are in this area, they will dry out faster and may need more than once a week watering. Those plants kept in a cooler, dimly lit area might only need water every 10 or 14 days. Our watering houseplant fact sheet (at www.soiltest.uconn.edu) may be of interest to new houseplant owners.

If plants receive too much water, the potting mix they are growing in becomes saturated. As this happens, any air in the root zone is pushed out and replaced by water. While this sounds counterintuitive to non-plant people, a plant’s roots need oxygen in the root zone to take up water. Once all the oxygen in the potting mix is replaced by water, the plant cannot take up water so they wilt. Usually the response to seeing a plant wilt is to add more water, thus exacerbating the problem.

What’s wrong with this plant?

Few roots, brown, unhealthy and overwatered.

Another scenario for wilting is caused by overfertilizing, especially with synthetic fertilizers, either in water-soluble or granular formulations. Fertilizers are primarily composed of nutrient salts. We use sodium chloride as our table salt at mealtimes, while some examples of fertilizer salts that are used to supply nutrients to plants include potassium chloride, ammonium nitrate and superphosphate.

You may have heard it mentioned that nature is always striving to reach an equilibrium (no matter how short lived it may be!). Well, if there are more nutrients in the potting mix, because of over-fertilization, than in the plant, curiously, the plant will release some of its water to try to dilute these salts so that the concentrations within the plant and surrounding the plant’s roots are more in line with one another, i.e. in equilibrium. In doing so, the plant loses water and wilts. On top of that the fertilizer salts can cause physical injury by the ‘burning’ or desiccation of plant root tissue. As plant roots die, there are less healthy ones to take up water so plants may still look water-deprived. Also injured roots because of overwatering or overfertilizing become susceptible to a variety of rot diseases.

Lastly, that plant that needs water on a daily basis probably is trying to tell you it needs to be repotted. There are so many roots growing in a restricted area that more water than you can supply it is needed. If plants are repotted on a regular basis, they are typically moved into pots that are one to two inches in diameter larger than the one they are presently growing in. If the roots are terribly overcrowded, you might select a pot that is 4 to 6 inches wider if the roots are not cut back. Do untangle or slice through encircling roots before repotting.

Spider plants need to be divided regularly to avoid overcrowding.

It is up to you, the houseplant caregiver, to figure out why your plant is wilting. Start by knocking the plant out of the pot and looking at the roots. They should be nice and white and crisp and the potting mix should be moderately moist but not dripping water or desert dry. If this is not so, try to figure out what has gone wrong. If you are stuck, please give us a call. Find our contact info at www.ladybug.uconn.edu

Happy Gardening,