Cultivating Questions: Purslane, Portahoopies and Plow Planted Peas

by Anne and Eric Nordell

In the Winter 2000 SFJ, we looked at a number of cover crop options for improving phosphorus availability. Option #419 was plow planted peas following double-cut rye. This cover crop sequence also turned out to be very effective at setting back purslane, a slippery weed which had so far eluded our cropping system in the house gardens. We would like to take the opportunity here to show how we used plow planted peas to reduce purslane pressure before planting the portahoopies.

For those not familiar with this tasty, nutritious weed, purslane can be a real challenge to manage in vegetable crops for a number of reasons. The seeds of this weed remain viable for many years in the garden, and generally do not germinate until hot weather — that is, after many of the market garden crops have already been planted. To make matters worse, this succulent plant often reroots after cultivation. Purslane also grows so close to the ground that it is impossible to control by mowing.

For all of these reasons, we have found that midsummer smother crops are more effective at controlling purslane than our usual cover crop/bare fallow sequence. These photos show just how we did it in the hot, dry summer of 1999. We repeated the same cover crop sequence in the cold, wet year of 2000 with equally good results, preparing a patch in the house garden for this year’s early hoophouse production.

#1: We clipped the cover crop of rye in this fallow area a couple of times during the spring of 1999. The resulting mulch of rye clippings shaded the soil sufficiently to prevent the purslane from germinating. Then, the end of July, we broadcast two types of pea seed on top of the rye clippings and plowed them in at the same time.

#2: We adjusted the old walking plow to cut a shallow furrow just 2-3″ deep. “Skim plowing” the rye residues placed the pea seed at the perfect depth for quick germination in hot, dry conditions. In fact, the heat loving cow peas popped out of the ground in just four days. On the other hand, it took almost twice as long for the cool season Canadian field peas to emerge, about the same time as the first of the purslane began to appear.

#3: As the weather cooled off toward the end of August, the field peas really took off, outgrowing their cousins from the South with vines four feet long. By using the two types of pea seed we effectively shaded out the purslane despite changes in the weather.

Yes, the purslane germinated and grew in the understory of the peas, but it did not receive enough sunlight to make seed. So you see, the key to our weed control strategy is the use of a well timed smother crop to intentionally germinate a generation or two of the purslane but prevent this weed from setting more seed. In this way, we can reduce the weed seed bank of purslane in the soil surface.

#4: By December, the July planted peas had already died off, producing a significant, soil protective mulch. At this point, we were no longer concerned about the purslane in the understory as it had long since died off with the first hard frost.

(Please be forewarned that this cover crop sequence of double-cut rye and plow planted peas is weed-specific. For example, it is not nearly as effective on winter weeds, such as chickweed, which tend to grow and make seed once the pea vines die back. We find that an oat/pea cover crop seeded thickly mid-August is much more reliable at suppressing winter weeds, because it remains standing, and shading the ground, until freezeup.)

#5: We like to move the portable hoophouses right on to the dead pea vines before the ground freezes hard so that these structures are ready for planting as soon as the snow melts in the spring. Unfortunately, we have not been able to come up with a greenhouse design which is strong enough to pull with the team — just imagine the stresses on a long structure when turning corners — but flexible enough to conform to the uneven terrain in these gardens.

Instead, we have adapted PVC hoophouse construction to come up with a design which is easy to dismantle and move by hand, and inexpensive to build. Costs of materials for the 20′ PVC pipes, rebar, rough cut hemlock lumber and plywood run under $200. The main limitation of the PVC hoophouse is it will not withstand a snowload so removing the greenhouse covering is necessary before the snow flies.

#6: After removing the six mil greenhouse plastic, the first step in relocating the portable hoophouse is carrying the twelve foot 4 by 4 sills to the new site, placing the beams in two rows twelve feet apart. Clearing a path through the pea residue, and shoveling away the stones, makes it much easier to seat the sill beams in the soil.

#7: We then drive twenty inch pieces of 3/4″ rebar into the holes drilled through the sill beams every four feet. The rebar is surprisingly easy to hammer into our stoney soil, and to remove by twisting them out with a vice-grip — no pipe puller necessary. And so far the rebar has anchored the portahoopies sufficiently to withstand some pretty stiff winds.

#8: Four inches of the rebar sticks above the sills so that we can slide PVC hoops over them.

#9: The hoops are connected at the top to the ridgepoles, also made of twenty foot pieces of 1″ PVC pipe. To move the hoops, we simply disconnect the ridgepoles from each other and drag the twenty foot sections of hoops over to the new site, and then…

#10: …reconnect them at the top again with PVC couplers. The hoops themselves are permanently attached to the ridgepoles with 1/4″ carriage bolts. We have found that heating the heads of the carriage bolts with a hand held torch helps to seat the bolts in the top of the PVC hoops so that they do not snag or rip the polyethylene greenhouse covering.

#11: The two of us can move one of these twenty by sixty foot structures in a few hours. Once the snow melts in the spring, we pull the greenhouse covering over the hoops and lath it to the sill beams and end walls.

(Take note that the simplicity of this design does not allow for roll up sides for cross ventilation. In our cool climate, we can get away with end-to-end venting through the 33″ by 66″ double doors for crops like salad mix and basil right through the summer. However, the hoophouse tomatoes would benefit from more air circulation, either through top venting skylights, or simply by reducing the length of these grow tunnels.)

One of the big advantages of the pea cover crop is the vines rot off at the base when they die. That makes it easy to rake off the residue before…

#12: …planting the first crops of the season in the portahoopies. Because these crops are planted intensively, we like to work in some well cured compost after removing the pea vines. The plow planted peas leave the soil so mellow and loose that hand forking the three 36″ beds goes pretty quickly.

This shot was taken toward the end of May in the cold, wet spring of 2000. At this time, our unprotected crops in the fields were struggling to grow, but we had already picked over this portahoopy spinach six times. Meanwhile, the heads of leaf lettuce in the second portahoopy were ready for harvest.

#13: We interplanted the lettuce with tomatoes, one row of tomatoes between two rows of lettuce on each bed. The trick to making this interplanting scheme work is planting the lettuce three weeks before the tomatoes are set out. This spacing, and timing, guarantees that neither crop crowds out the other, and that the lettuce comes off just as the tomatoes begin to blossom and need to be trellised.

Note the complete absence of purslane in the portahoopies despite the warm growing conditions in this protected environment. Even during the heat of summer, we only found a dozen of these creepy weeds in the understory of the tomatoes.

As we see it, the real value of the portahoopies is they allow us to extend our short growing season while still employing the principles of rotational cover cropping for weed control and building the soil.