As I sat on my front porch watching the “snow fall” of ash from the Florida wildfires this past May, it seemed very appropriate to write an article on drought tolerance. There’s nothing like the smell of wildfire smoke to bring out an appreciation for rain. Rain is a subject that many consumers across the United States are thinking about this year. In the floriculture industry, we tend to think of drought years as bad for business and they surely can be, but with a national wave of “green” philosophy and no sign of relief for drought-stricken areas, it is still our job to help growers, and consumers, succeed in gardening in times of little water.
If you are in a drought area of the United States, this article is for you. You can turn a drought into an opportunity to teach your grower staff how to grow drought-tolerant crops and your customers how to use them. When working with the public make sure to stress that even the most drought-tolerant plants need regular watering to get them established before reducing watering, remember consumers hear “drought tolerant” and figure it means “immortal without water.” Establishing plants in the landscape usually takes about two weeks of regular watering and then another two weeks of slow reduction.
This may seem like common sense, but it never hurts to have a refresher on some basics. If a plant is well adapted to drought, then it stands to reason it will require some changes in your basic production protocols to be produced under the lower light, cold wet soil, and luxury levels of water and nutrients we normally use to produce less drought-tolerant annuals. So the first thing to consider is how early do you want to bring these crops in? The earlier you start, the more critical good grower skills are.
Here is a breakdown of the major environmental factors you need to look at. Growers may want to pass this information along to retail customers as the same rules apply throughout the supply chain.
Light. Drought-tolerant plants prefer high light. It is part of the adaptation to drought in all sun-loving species. Many of these crops have fine hairs on the surface of the leaf to help break up high light levels when established in the landscape. For growers, the main point is to keep these plants in high light levels, hanging baskets or brighter production houses. A plant that loves high light is going to stretch that much more if produced in a low light setting.
Air circulation. Drought tolerance in plants is primarily the ability to manage water loss better than other plants. One way drought-tolerant species do this is by controlling water loss due to drying winds. A greenhouse with poor air circulation is problematic because the plants don’t have a way to control water uptake when there is no wind to move water out of the plant. Since these plants prefer good air circulation, they suffer in tightly packed, high-density plantings and generally use far less water than other crops. In fact, a lot of growers overwater these crops because their water needs are less than traditional annuals surrounding them on the bench. The main point is to make sure you have good air circulation in your production house. Horizontal airflow fans go a long way toward increasing crop quality.
Nutrients. In most production greenhouses, one fertilizer rate is applied to everything. For the most part this is fine for drought-tolerant species. Just manage your growing environment, and realize that when other factors are less than optimal, adding fertilizer isn’t going to help. A standard bedding plant fertilizer blend is fine for most of the crops mentioned here. If you are starting early in the season, definitely use a Cal-Mag formulation for low-light production. The extra calcium and magnesium will help keep the plant moisture levels in balance. Avoid high ammonium fertilizers during cold, cloudy weather.
Temperature. In most cases, drought tolerance also equates to a plant that likes high temperatures. These plants are going to be slower in cold conditions but really kick into growth with higher day temperatures. A general minimum temperature range is 65° F nights and 75° F days, but if you can raise that temperature, the plants will move through production faster.
Water. In general, drought-tolerant crops do not need as much water in production as other crops. In fact, it is a great way to encourage stem elongation. Working with your grower to keep drought-tolerant plants in an area where they can be kept on the dry side will save everyone a lot of problems as well as input costs in production.
So what happens when you can’t manage these factors with real precision? Well, you can expect to have some quality issues, likely will be using more plant growth regulators and learning a lot about Oedema.
Oedema is an environmental response to too much moisture in the plant and no way to move it through the plant’s system. As a result, the surface of the plant’s leaves begin to blister or pucker. Many growers assume there is a problem with the plant, but usually it is a problem with the growing environment.
If you see Oedema in your crops, increase air flow in the greenhouse, water early in the day to reduce the amount of water plants carry overnight and increase light and temperature levels during the day. Oedema has been in greenhouses since they were first developed, but in most cases some simple changes in greenhouse environment will solve the problem.
Cal-Mag fertilizer also will help as calcium and magnesium help maintain good membranes in the plant cells and avoid the symptoms of Oedema. Usually Oedema will go away if plants are moved to outdoor production but this isn’t always possible, so manage the environment and the problem takes care of itself.
Cuphea. There’s a lot of work being done to bring this genus to the market in a big way. Many breeders are developing hybrids, and almost every one of them will have standout performance under dry consumer conditions. Cuphea has a high oil content in the plant, which helps it to withstand low water conditions. Many species also have a layer of fine hairs on the surface of the leaf to control water loss under dry conditions and reduce the amount of light penetrating the leaf surface. This means they love high light and do really well in dry or very bright conditions. Many growers experience Oedema with this group so look for those that are Oedema resistant.
Chrysocephalum. This group of EX-Helichrysum (Yes, they changed the name) are making a rebound with a lot of new forms entering the market. Baby Gold was the old standard but look for improved foliage forms and differences in stem strength, from stiffly upright to more semi-trailing types. Usually yellow forms are best for foliage and orange forms are more ever-blooming, but both are excellent for hot-dry locations.
Lantana. Lantana is still growing rapidly in popularity despite some invasivity issues in Australia and the southern United States. This group of plants has so much to offer; they are bird and butterfly attractants and tough as nails in the landscape or containers. Most new breeding is aimed at taming their growth habit as older cultivars tend to get quite large. Northern growers should be careful of very dwarf types as their vigor in cold production can be very different from their performance later in the season when temperatures are high.
Oenothera. This genus is both tough and easy. They need good drainage and bright light, but many are tolerant of cool production conditions. Seed types range from 6 inches to 4 ft. tall and are beautiful and somewhat fragrant when in bloom. Definitely a genus to watch.
Penstemon. Here is a group that many growers struggle with because of early season low light and overwatering. But once you figure it out, this crop is amazingly easy and the sell-through is very fast. Different species and hybrids vary in their season of flower and most require deadheading to rebloom, but all-in-all, they’re great, especially perennial forms for western United States. As an annual or perennial, they look very spectacular in bloom.
Cleome. These may seem old fashioned, but new interspecific hybrids are changing and creating a new market for this crop. The interspecific types are nearly seed-free, meaning they offer an extended season of performance over traditional forms. This also reduces the risk of invasivity in certain areas of the United States. It’s available in great colors, like white, pink and purple. There is some risk of Oedema in early season, but they are fast growing, so use them as a quick crop 3-5 weeks to fill a gallon pot in mid to late spring. Ordering them in too early is a recipe for disaster as they grow so fast it’s easy to lose control of them.
Agastache. This is an emerging group of plants for which the breeding just gets better and better. Many are good perennials, but it is usually best to count them as annuals until you have some experience with their performance in your region. All have a wonderful menthol-mint fragrance to the foliage and are strong bee and hummingbird attractors, which is a sales plus. They love bright light, good air circulation and tolerate dryer landscape situations. All are Oedema resistant.
There are many options to look into in terms of drought-tolerant plants. This is only a small sampling. Remember, most drought-tolerant plants cannot be grown under the same conditions in which we grow traditional spring annuals. They need more light, more heat, more air circulation, and less water and fertilizer than the early spring crops. For growers to succeed, they need to plan ahead on timing and spacing of the crops. For retailers to succeed, they need to have a good understanding of how to position the crops and to plan on them being slightly later in spring or remarketed for the summer season.
This is just a short list of the possible crops you can use to deal with drought in your region. Focus on how to produce the crops in your greenhouse. At retail, the tag of drought tolerant, low water input is a sure selling point. Most consumers want less maintenance, and lower inputs, but they will only buy the plants if someone informs them of the benefits.