Thursday, July 30, 2009

Floating row covers and vegetable insects

A previous post discussed germinating seeds with the fabric dual-marketed as seed germination fabric and floating row covers. The fabric covers placed over the top of plants can serve several useful functions including shading plants when transplanting, and shading to extend the life of cool season vegetables as hot weather approaches. They are also used to capture heat for fall frost protection.

Row covers are easy to use. Throw loosely over plants allowing slack for future plant growth. You can also use covers over hoops or wire tunnels such as in the photo above right. Anchor to the soil with U-pins bent from wire and punched through the fabric that touches the ground. Soil also can be mounded over fabric edges to hold it down. Covers allow light and water through and stop movement of insects.

Looking at what insects are trapped under covers with vegetable plants and which are barred access is worthwhile. Row covers can stop plant damage from troublesome insects such as spinach leafminer, aphids, leafhoppers, cabbageworm and cabbage looper. Summer pest protection is offered against squash bug, cucumber beetle, bean beetle, corn earworm, whitefly and grasshopper.

Before declaring victory and thinking covers will solve all vegetable insect problems, remember that several insects spend part of their lives in the garden soil. When they emerge to find their favorite plant food enclosed in a cover that protects them from predator insects, they readily multiply. Examples are cutworms and slugs that lurk in scattered soil locations.

Some insects concentrate on the soil immediately around their host plant and can be thwarted by crop rotation. These include onion and seedcorn maggot, flea beetle, Colorado potato beetle, corn rootworm (left photo larva in soil and right adult on corn silks) and tomato hornworm. Planting in the same location and using floating row covers can set up insect problems with these plants.

If a pest does multiply under a row cover, it may be best to remove it to allow natural enemies such as lacewings and ladybird beetles access to the pests. Also remember that squash and other vegetables depend on insect pollination so be sure not to screen out bees during flowering.

Photo credits:
* Row cover over growing tunnel, David Whiting
* Larva of the western corn rootworm, Frank Peairs, Colorado State University,
* Western corn rootworm adult on corn silks, Tom Hlavaty, USDA Agricultural Research Service,

Thursday, July 23, 2009

Coping with hail damage

The hail storms that pounded the west Denver Metro area and Englewood early this week and later the Castle Rock area have prompted this post. Some landscapes took golf ball sized stones. My own garden received a 15 minute dose of marble sized hail leaving only the skeletons of tomatoes (click photo left to enlarge white hail stones and plant destruction details).

First, hail is generally accompanied by an ample amount of rain so stay out of the garden. Wet soil compacts easily and tramping on wet ground only worsens garden problems.
Another reason to stay out of the garden is that plants are more resilient than you may think. Don’t let the damage discourage you.

Most vegetables are annuals and respond to hail pruning with new growth. The limiting factor is the amount of growing season left to them before frost. Brittle plants such as peppers and large-leafed plants like squash (photo right) suffer the most. Leafy vegetables will re-grow and yield, root vegetables are protected underground and survive, and fruiting vegetables generally suffer the most.

Tomatoes tend to surprise in their ability to come back. My hope is that by hedging my bets through planting some shorter season Early Girl and cherry tomato types, I will still realize something where longer season heirloom types will probably not produce. The deep, extensive tomato root systems in my raised beds will help plants recover. I’ll keep you posted on this hope.

Once the water dries and its time to water again, I’ll begin using a weak fertilizer containing nitrate-type nitrogen in the water. Nitrate nitrogen signals plants to grow.

I will also continue sowing mid-summer vegetables for fall harvest as discussed in the July 2nd post. It’s not too late. Though I’m by nature accepting of hail events as a given in Colorado gardening, the act of planting does help soothe a gardener’s psyche. Doing something productive and once again seeing the wonder of germinating seeds is always energizing. Chins up intrepid Colorado gardeners!

Photo credit: Hail damaged tomatoes and Hail damaged crookneck squash, Carl Wilson

Wednesday, July 15, 2009

The Challenges of Summer Sowing

Mid-summer sowing of vegetable seed can be a challenge due to weed competition and warm soil temperature.

Weeds germinate quickly in summer and it can be difficult to tell the difference between weed seedlings and vegetable seedlings. One tip is to clear the soil surface of weed seeds by germinating and eliminating them. A week or more prior to sowing, water soil to germinate summer annual weeds such as purslane (see photo below left) and crabgrass and foxtail (photo below right).

Next use a sharp scuffle hoe to cut off the weeds from their roots, disturbing the soil as little as possible. Deep penetration of the soil will bring up additional weed seeds to germinate. Once the soil surface is cleared of weed plants, sow small seeded vegetables at the recommended shallow depth. Use germination fabric over them during germination (see March 6 post for how).

Warm soil temperatures can be a concern for germinating some seeds. The maximum soil temperature for germinating lettuce and spinach is 70 degrees F. The optimum temperature for germinating peas is 70 and many other vegetables 80 degrees F. Seeds become dormant at high temperatures.

Tips for avoiding warm temperature dormancy are to water soil before sowing and sow in the late afternoon so germination will begin overnight when soils are cooler. Shading the soil with seed germination fabric also helps.

Another tip is to pre-germinate seeds. The pea seeds (photo left) were soaked overnight indoors at room temperature (70 degrees F) in a moistened paper towel enclosed in a plastic bag. Do not soak longer or delicate seedling parts will be damaged in planting.

Pre-germinating small seedlings is more difficult. Solve this through fluid seeding. Germinate small seeds on a moistened paper towel in a closed plastic container kept indoors at 70 degrees F. Don’t allow seeds to germinate for more than a few days, only until they just break out of their seed coat. Wash germinating seed off the towel into a sieve with a gentle stream of room temperature water.

Gently stir germinated seeds into pre-prepared fluid seeding gel. The gel is made by dissolving 2 to 3 tablespoons of cornstarch in boiling water and cooling to room temperature. Add the gel-seed mixture to a plastic bag, seal, snip off one corner and gently squeeze the gel onto moistened soil. Cover as recommended and use seed germination fabric to shade. Keep fabric in place until green seedlings are readily apparent. Remove fabric and water carefully until seedlings are growing vigorously.

Crabgrass, purslane and soaked pea seed photos credit – Carl Wilson

Wednesday, July 8, 2009

The Mean Season is Here

The arrival of ninety degree F temperatures this week is tough on Front Range gardeners used to a cool spring but even tougher on plants. Plants can’t get up and go inside for a cool drink when things heat up!

Plants that grew up in a cool environment aren’t tough enough to take hot, dry conditions. Their cells and structure are simply wimpy. Expect to see some heat stress, leaf scorch, blossom drop and bolting in the garden.

To help plants transition to the heat, water with care. Vegetables like most plants need some soil drying between waterings but don’t let soils dry completely. This is especially critical until leaf tissue toughens. Some vegetables (tomatoes) benefit from more soil drying than others (onions and carrots). Bean blossoms (photo right) drop when short on moisture and pods fail to fill; they require the most moisture of any vegetable.

One note on America’s most popular garden vegetable, the tomato. Fluctuations in water supply, either excessively wet or dry will cause blossom end rot. This could have been triggered in June downpours or by July heat. It begins as a light tan, water-soaked spot on the blossom end of the fruit (photo left). These spots turn brown to black and leathery and there is no correcting it once the damage is done. Future blossoms that set fruit when moisture conditions are better won't be affected by damage to previous fruit. To manage this condition, fertilize and water properly. Use mulch to reduce moisture fluctuations.

Want more specific watering tips? Check Colorado State University Extension's Water Conservation in the Vegetable Garden garden note.

Bean blossom photo credit, Carl Wilson
Blossom end rot photo credit, Colorado State University Extension

Thursday, July 2, 2009

It’s time to seed fall vegetables

Although it may seem that vegetable gardens have just begun growing well and planting is done, it’s time to seed crops for fall harvest. Sixty day crops planted in July will mature in September as weather is cooling.

Look at seed packets and note the days to harvest. Count back from the first fall frost date, October 11 for the Denver area. With cool season vegetables note that many tolerate the first light frosts of fall very well and an extended harvest period can be expected. Warm season vegetables must be planted to mature well before frost when temperatures remain warm.

Here are some vegetable planting suggestions listed with their typical days to harvest. Cool season vegetables such as peas (65), cabbage (85), collards (55), broccoli (65), kale (60), spinach (40), lettuce (60) and endive (45) are good candidates. Root vegetables such as beets (60), carrots (70) and turnips (50) can be planted this month. Even some fruiting vegetables such as bush beans (60) and cucumbers (55) can still be planted if done by mid-July. The very short season radish (30) can be planted into August with success.

Note that peas planted for fall harvest (photo above) are prone to powdery mildew. Choose powdery mildew resistant varieties. Be sure to provide support such as netting stapled on posts (right) for them to climb to insure good air circulation. Often harvests are reduced as compared to spring plantings. I’m willing to gamble on these Oregon Sugar Pod II’s because I like snowpeas and have a separate area where the air movement is not blocked by tomatoes or other vegetables.

Planting fall crops in “succession” where other spring crops have been harvested is a way to extend harvests past the first frosts and maximize yields from your garden.

Photo credit planted pea seeds and pea netting - Carl Wilson