Q. We cannot seem to grow lettuce that is not bitter, even when we water frequently. We've even had our soil tested. Any suggestions? Thanks.
- --Judy in Ohio
A. Well, variety choice counts for a lot; the heirloom variety "Deer Tongue" is said to be able to hold its flavor the best in the face of stress. But you're right to focus on moisture. As with hot peppers and garlic, stress from lack of water can make even the sweetest lettuce taste bitter. And an article we did back when I was Editor of ORGANIC GARDENING magazine noted that lettuce must also be kept growing fast to be at its sweetest. The author of that story recommended a once a week feeding with a dilute solution of fish emulsion to keep it happy, healthy and sweet. I'm using a fish and seaweed mix on my 'off-season' lettuce as we speak, and so far so good.
A nice soil-cooling mulch of compost or shredded leaves will also help. And as late Spring heat starts to build, some shade. Professionals use shade cloth; I place my last runs behind tall plants like tomatoes or sweet corn, or in a location that just gets afternoon shade. To try and saladicize into the heart of Summer, try these cooling voodoos with "Deer Tongue"; or "Slobolt", a variety said to have good flavor in summer if given lots of water, regular food and a lot of shade.
But most varieties of lettuce—and virtually all spinach—will bolt and send up a tall central stalk when serious heat arrives, signaling the arrival of beaucoup bitterness. (White sap will also be visible when you harvest with scissors.) That's when all but the most dedicated, courageous, stubborn or just plain ignorant among us give up until the fall. Or we'll switch to collard greens (which will survive summer, but not taste nearly as good as when they're grown in cooler weather), Swiss chard, or—our alleged topic today—one of the two heat-loving greens used as summertime spinach substitutes, which I have a bad habit of lumping together and simply calling "New Zealand Spinach", which leads us to…
Q. Hello Mike! We heard you talking about New Zealand spinach on a recent show. You should try Malabar spinach, a gorgeous ornamental vine with beautiful glossy green leaves and red stems. Unlike what you have implied in past shows, New Zealand and Malabar spinach are different plants. My husband has grown both (although he doesn't believe that New Zealand is a true spinach), and prefers the Malabar. Some of the leaves he measured were 9" X 12". We had to order the seeds for both plants from catalogue; apparently no one around here likes to grow them.
- ---A mysterious couple from East Texas who don't want their names—even just their first names--used on the radio
A. You are correct, oh nameless ones! New Zealand spinach, a member of the family Tetragonia, is not a true spinach (whose scientific name, Spinacia, is a lot like its English one). NZS is a ground hugger, and perennial in really warm climes. You harvest it by trimming off the new young leaves from its shoots. Something of an acquired taste, it is said to pass better as a spinach substitute when it's cooked than raw.
Ah, but despite its uncanny resemblance to the real thing, your favored plant, Malabar Spinach (also known as "African climbing spinach") is not a true spinach either. (Pity then the poor Popeye who reaches for either in desperation when being beaten up by Bluto after the Fourth of July!) This vining member of the Basella family can take even more intense summer heat than the New Zealand type. Its thick succulent leaves are also said to be an acquired taste; Southern garden writer Lois Trigg Chaplin described it as 'slimy'. But that's also what Northerners say about okra.
Q. My girlfriend and I heard you talking about New Zealand spinach and were excited about the possibility of growing good greens during the summer. However, some sources say the leaves contain toxins and you have to blanch them before you can safely consume them. Other sources don't mention toxins or blanching. Could you settle this conflict? And if New Zealand spinach does contain toxins, could you recommend other hot weather greens that work in our climate? Thanks; we love the show!
- ---Matt (and Vanessa) in Lewes, Delaware
A. Well kids, the same so-called 'toxic compound' (oxalic acid) exists in regular spinach as well; and apparently in much higher amounts. And while a Wikipedia article about New Zealand spinach does mention the blanching thing, several scientific and medical sites I checked said that blanching is a ruse. It doesn't seem to lower the oxalate levels in regular spinach significantly, but it does leach out a lot of nutrition.
This has been a subject of debate regarding regular spinach for decades, and we won't settle it here; other than to say that people with certain medical conditions should avoid diets high in oxalic acid, which can be a drag, because this naturally occurring compound is found in a lot of super-healthy foods, including most nuts and berries.
Two bottom lines: 1) If you eat regular spinach with abandon, a food with one of the highest known oxalic acid contents, I wouldn't worry about the New Zealand type. 2) By all accounts, the more spinachy-looking Malabar type is vastly superior in nutritional content to New Zealand, and by my ciphering, more nutritious than perhaps even spinach itself. So that might be the better green to grow for fresh eating in August.
Or try late runs of Slobolt, Deer Tongue and other heat-hearty lettuces in a spot that gets afternoon shade. Mulch them well, mist every morning, keep them well-watered, feed with dilute fish emulsion or a fish and seaweed mix once a week, and praise every time you cut leaves without seeing white sap.
Resources: Here's some basic spinach info from Wikipedia. Here's some info from a great international site about Malabar Spinach and New Zealand Spinach. And finally, here are the Wikipedia entries on Malabar and New Zealand Spinaches.