diff --git a/redwood-layout-composeui/api/redwood-layout-composeui.klib.api b/redwood-layout-composeui/api/redwood-layout-composeui.klib.api
index fc79d342b8..0b4e9fe349 100644
--- a/redwood-layout-composeui/api/redwood-layout-composeui.klib.api
+++ b/redwood-layout-composeui/api/redwood-layout-composeui.klib.api
@@ -30,8 +30,10 @@ final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_Bo
 final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_BoxMeasurePolicy$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_BoxMeasurePolicy$stableprop|#static{}app_cash_redwood_layout_composeui_BoxMeasurePolicy$stableprop[0]
 final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeMeasureCallback$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeMeasureCallback$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeMeasureCallback$stableprop[0]
 final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiBox$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiBox$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeUiBox$stableprop[0]
+final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiColumn$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiColumn$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeUiColumn$stableprop[0]
 final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiFlexContainer$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiFlexContainer$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeUiFlexContainer$stableprop[0]
 final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRedwoodLayoutWidgetFactory$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRedwoodLayoutWidgetFactory$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeUiRedwoodLayoutWidgetFactory$stableprop[0]
+final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRow$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRow$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeUiRow$stableprop[0]
 final val app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiSpacer$stableprop // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiSpacer$stableprop|#static{}app_cash_redwood_layout_composeui_ComposeUiSpacer$stableprop[0]
 
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_BoxChildLayoutInfo$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_BoxChildLayoutInfo$stableprop_getter|app_cash_redwood_layout_composeui_BoxChildLayoutInfo$stableprop_getter(){}[0]
@@ -39,6 +41,8 @@ final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_Bo
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_BoxMeasurePolicy$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_BoxMeasurePolicy$stableprop_getter|app_cash_redwood_layout_composeui_BoxMeasurePolicy$stableprop_getter(){}[0]
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeMeasureCallback$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeMeasureCallback$stableprop_getter|app_cash_redwood_layout_composeui_ComposeMeasureCallback$stableprop_getter(){}[0]
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiBox$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiBox$stableprop_getter|app_cash_redwood_layout_composeui_ComposeUiBox$stableprop_getter(){}[0]
+final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiColumn$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiColumn$stableprop_getter|app_cash_redwood_layout_composeui_ComposeUiColumn$stableprop_getter(){}[0]
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiFlexContainer$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiFlexContainer$stableprop_getter|app_cash_redwood_layout_composeui_ComposeUiFlexContainer$stableprop_getter(){}[0]
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRedwoodLayoutWidgetFactory$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRedwoodLayoutWidgetFactory$stableprop_getter|app_cash_redwood_layout_composeui_ComposeUiRedwoodLayoutWidgetFactory$stableprop_getter(){}[0]
+final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRow$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiRow$stableprop_getter|app_cash_redwood_layout_composeui_ComposeUiRow$stableprop_getter(){}[0]
 final fun app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiSpacer$stableprop_getter(): kotlin/Int // app.cash.redwood.layout.composeui/app_cash_redwood_layout_composeui_ComposeUiSpacer$stableprop_getter|app_cash_redwood_layout_composeui_ComposeUiSpacer$stableprop_getter(){}[0]
diff --git a/redwood-layout-composeui/src/androidUnitTest/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainerTest.kt b/redwood-layout-composeui/src/androidUnitTest/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainerTest.kt
index 4872ef4a00..7f643ba239 100644
--- a/redwood-layout-composeui/src/androidUnitTest/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainerTest.kt
+++ b/redwood-layout-composeui/src/androidUnitTest/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainerTest.kt
@@ -24,11 +24,14 @@ import app.cash.paparazzi.DeviceConfig
 import app.cash.paparazzi.Paparazzi
 import app.cash.redwood.layout.AbstractFlexContainerTest
 import app.cash.redwood.layout.TestFlexContainer
+import app.cash.redwood.layout.api.Constraint
+import app.cash.redwood.layout.api.Overflow
+import app.cash.redwood.layout.widget.Column
+import app.cash.redwood.layout.widget.Row
 import app.cash.redwood.layout.widget.Spacer
 import app.cash.redwood.snapshot.testing.ComposeSnapshotter
 import app.cash.redwood.snapshot.testing.ComposeUiTestWidgetFactory
 import app.cash.redwood.ui.Px
-import app.cash.redwood.widget.compose.ComposeWidgetChildren
 import app.cash.redwood.yoga.FlexDirection
 import com.android.resources.LayoutDirection
 import kotlinx.coroutines.runBlocking
@@ -51,18 +54,26 @@ class ComposeUiFlexContainerTest(
   override fun flexContainer(
     direction: FlexDirection,
     backgroundColor: Int,
-  ): ComposeTestFlexContainer {
+  ): TestFlexContainer<@Composable () -> Unit> {
     return ComposeTestFlexContainer(direction, backgroundColor)
-      .apply { applyDefaults() }
+      .apply { (this as TestFlexContainer<*>).applyDefaults() }
   }
 
-  override fun row() = flexContainer(FlexDirection.Row)
+  override fun row(): Row<@Composable () -> Unit> = ComposeUiRow()
+    .apply {
+      container.testOnlyModifier = Modifier.background(Color(defaultBackgroundColor))
+      applyDefaults()
+    }
 
-  override fun column() = flexContainer(FlexDirection.Column)
+  override fun column(): Column<@Composable () -> Unit> = ComposeUiColumn()
+    .apply {
+      container.testOnlyModifier = Modifier.background(Color(defaultBackgroundColor))
+      applyDefaults()
+    }
 
   override fun spacer(backgroundColor: Int): Spacer<@Composable () -> Unit> {
     // TODO: honor backgroundColor.
-    return ComposeUiRedwoodLayoutWidgetFactory().Spacer()
+    return ComposeUiSpacer()
   }
 
   override fun snapshotter(widget: @Composable () -> Unit) = ComposeSnapshotter(paparazzi, widget)
@@ -71,7 +82,6 @@ class ComposeUiFlexContainerTest(
     private val delegate: ComposeUiFlexContainer,
   ) : TestFlexContainer<@Composable () -> Unit>,
     YogaFlexContainer<@Composable () -> Unit> by delegate {
-    override val children: ComposeWidgetChildren = delegate.children
 
     constructor(direction: FlexDirection, backgroundColor: Int) : this(
       ComposeUiFlexContainer(direction).apply {
@@ -79,9 +89,15 @@ class ComposeUiFlexContainerTest(
       },
     )
 
-    override fun onScroll(onScroll: ((Px) -> Unit)?) {
-      delegate.onScroll(onScroll)
-    }
+    override val value get() = delegate.value
+    override var modifier by delegate::modifier
+
+    override val children get() = delegate.children
+
+    override fun width(width: Constraint) = delegate.width(width)
+    override fun height(height: Constraint) = delegate.height(height)
+    override fun overflow(overflow: Overflow) = delegate.overflow(overflow)
+    override fun onScroll(onScroll: ((Px) -> Unit)?) = delegate.onScroll(onScroll)
 
     override fun scroll(offset: Px) {
       runBlocking {
diff --git a/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainer.kt b/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainer.kt
index ff3056dcf7..92b2b060f9 100644
--- a/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainer.kt
+++ b/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiFlexContainer.kt
@@ -46,6 +46,8 @@ import app.cash.redwood.layout.api.Constraint
 import app.cash.redwood.layout.api.CrossAxisAlignment
 import app.cash.redwood.layout.api.MainAxisAlignment
 import app.cash.redwood.layout.api.Overflow
+import app.cash.redwood.layout.widget.Column
+import app.cash.redwood.layout.widget.Row
 import app.cash.redwood.ui.Density
 import app.cash.redwood.ui.Margin
 import app.cash.redwood.ui.Px
@@ -56,6 +58,38 @@ import app.cash.redwood.yoga.Node
 import app.cash.redwood.yoga.Size
 import app.cash.redwood.yoga.isHorizontal
 
+internal class ComposeUiColumn : Column<@Composable () -> Unit> {
+  internal val container = ComposeUiFlexContainer(FlexDirection.Column)
+
+  override val value get() = container.value
+  override var modifier by container::modifier
+  override val children get() = container.children
+
+  override fun width(width: Constraint) = container.width(width)
+  override fun height(height: Constraint) = container.height(height)
+  override fun margin(margin: Margin) = container.margin(margin)
+  override fun overflow(overflow: Overflow) = container.overflow(overflow)
+  override fun horizontalAlignment(horizontalAlignment: CrossAxisAlignment) = container.horizontalAlignment(horizontalAlignment)
+  override fun verticalAlignment(verticalAlignment: MainAxisAlignment) = container.verticalAlignment(verticalAlignment)
+  override fun onScroll(onScroll: ((Px) -> Unit)?) = container.onScroll(onScroll)
+}
+
+internal class ComposeUiRow : Row<@Composable () -> Unit> {
+  internal val container = ComposeUiFlexContainer(FlexDirection.Row)
+
+  override val value get() = container.value
+  override var modifier by container::modifier
+  override val children get() = container.children
+
+  override fun width(width: Constraint) = container.width(width)
+  override fun height(height: Constraint) = container.height(height)
+  override fun margin(margin: Margin) = container.margin(margin)
+  override fun overflow(overflow: Overflow) = container.overflow(overflow)
+  override fun horizontalAlignment(horizontalAlignment: MainAxisAlignment) = container.horizontalAlignment(horizontalAlignment)
+  override fun verticalAlignment(verticalAlignment: CrossAxisAlignment) = container.verticalAlignment(verticalAlignment)
+  override fun onScroll(onScroll: ((Px) -> Unit)?) = container.onScroll(onScroll)
+}
+
 internal class ComposeUiFlexContainer(
   private val flexDirection: FlexDirection,
 ) : YogaFlexContainer<@Composable () -> Unit> {
@@ -85,6 +119,7 @@ internal class ComposeUiFlexContainer(
   }
 
   override fun margin(margin: Margin) {
+    super.margin(margin)
     this.margin = margin
   }
 
diff --git a/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiRedwoodLayoutWidgetFactory.kt b/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiRedwoodLayoutWidgetFactory.kt
index 7df88755bd..ccae48fe5f 100644
--- a/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiRedwoodLayoutWidgetFactory.kt
+++ b/redwood-layout-composeui/src/commonMain/kotlin/app/cash/redwood/layout/composeui/ComposeUiRedwoodLayoutWidgetFactory.kt
@@ -21,11 +21,10 @@ import app.cash.redwood.layout.widget.Column
 import app.cash.redwood.layout.widget.RedwoodLayoutWidgetFactory
 import app.cash.redwood.layout.widget.Row
 import app.cash.redwood.layout.widget.Spacer
-import app.cash.redwood.yoga.FlexDirection
 
 public class ComposeUiRedwoodLayoutWidgetFactory : RedwoodLayoutWidgetFactory<@Composable () -> Unit> {
   override fun Box(): Box<@Composable () -> Unit> = ComposeUiBox()
-  override fun Column(): Column<@Composable () -> Unit> = ComposeUiFlexContainer(FlexDirection.Column)
-  override fun Row(): Row<@Composable () -> Unit> = ComposeUiFlexContainer(FlexDirection.Row)
+  override fun Column(): Column<@Composable () -> Unit> = ComposeUiColumn()
+  override fun Row(): Row<@Composable () -> Unit> = ComposeUiRow()
   override fun Spacer(): Spacer<@Composable () -> Unit> = ComposeUiSpacer()
 }
diff --git a/redwood-layout-shared-test/src/commonMain/kotlin/app/cash/redwood/layout/AbstractFlexContainerTest.kt b/redwood-layout-shared-test/src/commonMain/kotlin/app/cash/redwood/layout/AbstractFlexContainerTest.kt
index 2dcead9b98..8322223cc2 100644
--- a/redwood-layout-shared-test/src/commonMain/kotlin/app/cash/redwood/layout/AbstractFlexContainerTest.kt
+++ b/redwood-layout-shared-test/src/commonMain/kotlin/app/cash/redwood/layout/AbstractFlexContainerTest.kt
@@ -43,9 +43,11 @@ import kotlin.test.assertTrue
 abstract class AbstractFlexContainerTest<T : Any> {
   abstract val widgetFactory: TestWidgetFactory<T>
 
+  protected val defaultBackgroundColor = argb(51, 0, 0, 255)
+
   abstract fun flexContainer(
     direction: FlexDirection,
-    backgroundColor: Int = argb(51, 0, 0, 255),
+    backgroundColor: Int = defaultBackgroundColor,
   ): TestFlexContainer<T>
 
   /**
@@ -63,6 +65,36 @@ abstract class AbstractFlexContainerTest<T : Any> {
     onScroll(null)
   }
 
+  /**
+   * Yoga node’s default values for properties like alignment are different from Redwood's default
+   * values, so we explicitly apply those defaults here. This is only necessary in tests; in
+   * production the framework explicitly sets every property.
+   */
+  protected fun Row<*>.applyDefaults() {
+    width(Constraint.Wrap)
+    height(Constraint.Wrap)
+    margin(Margin.Zero)
+    overflow(Overflow.Clip)
+    verticalAlignment(CrossAxisAlignment.Start)
+    horizontalAlignment(MainAxisAlignment.Start)
+    onScroll(null)
+  }
+
+  /**
+   * Yoga node’s default values for properties like alignment are different from Redwood's default
+   * values, so we explicitly apply those defaults here. This is only necessary in tests; in
+   * production the framework explicitly sets every property.
+   */
+  protected fun Column<*>.applyDefaults() {
+    width(Constraint.Wrap)
+    height(Constraint.Wrap)
+    margin(Margin.Zero)
+    overflow(Overflow.Clip)
+    horizontalAlignment(CrossAxisAlignment.Start)
+    verticalAlignment(MainAxisAlignment.Start)
+    onScroll(null)
+  }
+
   protected fun <T : Any> TestFlexContainer<T>.add(widget: Widget<T>) {
     addAt(children.widgets.size, widget)
   }
diff --git a/redwood-layout-uiview/src/commonTest/kotlin/app/cash/redwood/layout/uiview/UIViewFlexContainerTest.kt b/redwood-layout-uiview/src/commonTest/kotlin/app/cash/redwood/layout/uiview/UIViewFlexContainerTest.kt
index c744a57993..dd39353108 100644
--- a/redwood-layout-uiview/src/commonTest/kotlin/app/cash/redwood/layout/uiview/UIViewFlexContainerTest.kt
+++ b/redwood-layout-uiview/src/commonTest/kotlin/app/cash/redwood/layout/uiview/UIViewFlexContainerTest.kt
@@ -62,7 +62,7 @@ class UIViewFlexContainerTest(
         }
       }
 
-      applyDefaults()
+      (this as TestFlexContainer<*>).applyDefaults()
     }
   }
 
diff --git a/redwood-layout-view/src/test/kotlin/app/cash/redwood/layout/view/ViewFlexContainerTest.kt b/redwood-layout-view/src/test/kotlin/app/cash/redwood/layout/view/ViewFlexContainerTest.kt
index 840141258a..d0a1995346 100644
--- a/redwood-layout-view/src/test/kotlin/app/cash/redwood/layout/view/ViewFlexContainerTest.kt
+++ b/redwood-layout-view/src/test/kotlin/app/cash/redwood/layout/view/ViewFlexContainerTest.kt
@@ -54,7 +54,7 @@ class ViewFlexContainerTest(
       value.setBackgroundColor(backgroundColor)
     }
     return ViewTestFlexContainer(delegate)
-      .apply { applyDefaults() }
+      .apply { (this as TestFlexContainer<*>).applyDefaults() }
   }
 
   override fun row() = flexContainer(FlexDirection.Row)