Identify water spinach for pad pak boong and prepare the stir-fry

What Thai stir-fried morning glory is and when to make it

Pad pak boong, also written pak boong fai daeng, is a Thai stir-fry of water spinach cooked quickly with garlic, chilies and a salty, savory sauce. The goal is a green vegetable that is just wilted and hot all the way through. Its hollow stems should stay distinct from its soft leaves, and it should be coated in a garlicky sauce rather than stewed in liquid. In the Hot Thai Kitchen version described below, it is served with jasmine rice or plain congee. That makes it a fast vegetable dish to cook alongside a rice-based meal.

Identify the right vegetable: water spinach, not just any morning glory

The vegetable sold for this dish as morning glory is water spinach. Its botanical name is Ipomoea aquatica, in the family Convolvulaceae. An older name, Ipomoea reptans, refers to the same species. Singapore's National Parks Board lists kangkong and water morning glory among its common names. It records the leaves and stems as edible and notes they are often stir-fried.

Features that identify water spinach:
Hollow stems
Smooth leaves, not hairy or textured
Leaves arranged alternately along the stem, not in opposite pairs
Arrow-shaped leaves

The words morning glory are shared by other plants, including garden ornamentals. A shared common name does not mean a plant is the same species or that it is edible. Buy the vegetable labeled water spinach, kangkong or pak boong, or confirm it as Ipomoea aquatica. Do not substitute a plant just because it is called morning glory.

Ingredients for pad pak boong

These quantities come from Hot Thai Kitchen's recipe for one batch built around 150 g of water spinach.

Ingredient	Amount	Preparation
Water spinach	150 g	Stems cut into 2–3-inch pieces; leaves left whole
Garlic	5–6 cloves	Pounded coarsely
Thai chilies	2–3	Pounded finely
Oyster sauce	1 tbsp	Mixed into the sauce
Tao jiew (fermented soybean paste)	1 tbsp	Mixed into the sauce
Soy sauce	½ tbsp	Mixed into the sauce
Sugar	1 tsp	Mixed into the sauce
White pepper	printed as ¼–⅛ tsp	Mixed into the sauce
Oil	2 tbsp	For frying the aromatics
Water	2–4 tbsp	Added only if the pan looks dry

Tao jiew is a fermented soybean paste. It is a different product from soy sauce, so the two are not interchangeable, and this recipe uses both. Check jar labels so you do not grab soy sauce twice.

The white pepper amount is printed in reverse order on the recipe card, as ¼–⅛ tsp. The two endpoints are ⅛ tsp and ¼ tsp. Choose within that span according to how strongly you want the pepper to come through.

Equipment

A mortar and pestle, for pounding the chilies and garlic
A small bowl, for mixing the sauce
A pan that can handle high heat
A serving plate, ready before you start cooking

How to cook it, step by step

1. Prepare the water spinach. Cut the stems into 2–3-inch sections and keep the leaves whole.
2. Make the sauce. Stir the oyster sauce, tao jiew, soy sauce, sugar and white pepper together. Keep stirring until the sugar has dissolved.
3. Pound the aromatics. Pound the chilies until fine. Pound the garlic only coarsely, so it keeps some texture.
4. Fry the aromatics. Heat the oil over high heat and add the garlic and chilies. Fry until the garlic just begins to brown.
5. Add the vegetable and sauce. Add the water spinach and the sauce together. Toss continuously until the greens are lightly wilted and heated through.
6. Adjust the moisture. If the pan looks dry, add water a little at a time, up to 2–4 tbsp.
7. Plate right away. Move the stir-fry to the plate as soon as it is done, and serve it with jasmine rice or plain congee.

How to judge each stage

Sauce: there should be no grains of sugar left when you stir it.
Garlic in the oil: it should just start to brown. That signals it is time to add the vegetable and sauce.
Vegetable: it should be lightly wilted and hot through, not collapsed.
Moisture: if the pan looks dry and the sauce is not coating the greens, add a splash of water.
Finish: once the greens reach the lightly wilted stage, take them out of the pan immediately. If they stay in the pan, they keep cooking.

Course corrections

If the stir-fry looks dry once the greens are in, add water gradually, up to 2–4 tbsp. Stop adding as soon as the sauce coats the vegetable. If you are unsure whether the vegetable you bought is water spinach, check it against the identification features above before cooking. If it does not match, do not use it.

Illustrative example: planning a larger batch

This is a hypothetical planning worksheet, not a tested recipe. Suppose you plan to cook 300 g of water spinach. Dividing 300 by 150 gives a multiplier of 2. Write down the scaled amounts before you start, along with the species you confirmed and the label of each condiment.

Ingredient	150 g batch	300 g plan (×2)
Water spinach	150 g	300 g
Garlic	5–6 cloves	10–12 cloves
Thai chilies	2–3	4–6
Oyster sauce	1 tbsp	2 tbsp
Tao jiew	1 tbsp	2 tbsp
Soy sauce	½ tbsp	1 tbsp
Sugar	1 tsp	2 tsp
White pepper	⅛–¼ tsp (printed ¼–⅛)	¼–½ tsp
Oil	2 tbsp	4 tbsp
Water, as needed	2–4 tbsp	4–8 tbsp