Green Man Publishing

Spinach

Spinacia oleracea

Introduction: Spinach originated in Asia and reached Europe during the Middle Ages. It is one of the most popular leaf vegetables because it is quick and highly productive. The harvest can start within a month of planting and it can be out of the ground within 2 months.

Climate: This is very much a cool weather crop, growing best at a mild 60 – 65°F during the day and even lower at night (down to 40 – 45°F). It is quite hardy and can tolerate temperatures as low as 20°F.

Spinach doesn’t like hot weather and will be unhappy (and probably bolt) when it gets above 75°F.

Nutritional content: Spinach is rich in iron, but this is very water soluble and easily leached out by boiling. It is also a source of vitamins A (beta carotene), C and K, folate, luteine and various useful phytochemicals. It contains about 100 calories per pound.

Spinach also contains mildly toxic oxalic acid, which can make calcium somewhat less available in the body. Fortunately this is not a significant problem to anyone with a reasonable intake of calcium. You will still get more calcium from eating spinach than you will lose from ingesting the oxalic acid.

Oxalic acid may also contribute to the formation of kidney stones, so anyone prone to them should probably avoid spinach.

Ease of growing: As with many other crops, spinach is easy to grow if you give it the right conditions, which in this case means cool weather and short days. It is usually grown as a spring and fall crop, with the latter being easiest. Forget about trying to grow spinach in warm weather, no sooner does it reach any size than it bolts (in fact it sometimes bolts before it reaches any size at all!) 

About Spinach  

Seed facts
Germ temp: 35 (55 – 65) 75°F
Germination time: 5 – 22 days
62 days / 32°F
22 days / 41°F
12 days / 50°F * Optimum
7 days / 59°F
6 days / 68°F
5 days / 77°F
Seed viability: 2 – 4 years
Germination percentage: 60%
Weeks to grow transplants: 3 – 4  

Planning facts
Hardiness: Hardy
Growing temp: 60 – 65°F day
                         40 – 45°F night
Plants per person: 10 per planting
Plants per sq ft: 9  

Planting
Spring crop:
Start: 8 wks before last frost
Plant out: 4 wks before last frost
Direct sow:
Spring: 6 wks before last frost
Fall: 6 – 8 wks before first frost
Succession sow: Every 2 wks  

Harvest facts
Days to harvest: 40 – 60
Yield per plant: 6 – 8 oz
Yield per sq ft: ½ – 2 lb sq ft
 

Soil

pH 6.0 (6.5) 7.0

Spinach is a fast growing and fairly hungry plant and does best in a soil that is rich in humus, moisture retentive and contains lots of nitrogen and potassium. A light and well-drained soil is best as it will warm up quickly in spring. It should also be fairly neutral as spinach doesn’t like acid soil. It is quite tolerant of saline soil.

Soil preparation: For best growth spinach needs a steady supply of available nutrients. It likes organic matter, so incorporate 2˝ of compost or aged manure into the top 10˝ of soil (where most feeder roots are found), along with a fertilizer mix. It loves manure and can even thrive in soil containing fresh manure (though ideally this should be incorporated the previous autumn).

Spinach doesn’t like acid soil, so lime if necessary. Not too much lime though, as it doesn’t like very alkaline soil either!

Planning

Where: Spinach really doesn’t like heat and in warmer areas it will do better on a site that has light shade during the hottest part of the day. When growing in cool weather it should be in full sun. Raised beds are good because they warm up quickly in spring and tend to be well-drained.

Rotate spinach (and the related beet, chard and quinoa) so it doesn’t grow in the same place for at least 3 years. The plants should have good air circulation to minimize disease problems.

When: More than any other common crop, spinach doesn’t like warm weather, in fact it actually germinates best at only 50°F. If you look at Seed facts you will notice that it germinates more rapidly at higher temperatures, but less seed will germinate. At 70°F only about half of the seeds may germinate.

You have several options of when to grow spinach:

Spring: You must sow spinach early if you are to get a useful crop before heat and lengthening days cause it to bolt. Start the first spinach plants indoors about 8 weeks before the last frost date and plant it out about 4 weeks later. Direct sow your first outdoor crop 6 weeks before the last frost date.

Don’t stop with one planting, you should be able to make 2 – 3 succession sowings 2 weeks apart, and maybe more, depending upon how quickly the weather warms up.

Summer: If you live in a climate with cool summers you may be able to grow spinach right through the summer. Just succession sow every 2 – 3 weeks.

If you don’t have cool summers then forget about spinach, there are plenty more fish in the sea. See Warm weather alternatives to spinach below.

Autumn: Spinach does best as a fall crop, as it is much less prone to bolting in the shorter, cooler days and the leaves grow larger and more succulent. Sow the seeds when the soil starts to cool down, which may be a couple of months before the first autumn frost date.

The biggest problem when planting fall spinach comes when the soil is too warm. It must be cool enough for good germination (ideally below 60°F), otherwise germination may be poor. To improve your chances you might try cooling the soil by frequent watering, and using shade cloth. Another option is to pre-germinate the seed in the fridge. Put the seeds on a moist paper towel, put it in a plastic bag and store in the fridge for a week. They should then germinate quite well.

Winter: In areas with mild winters, some varieties of spinach can be grown as a winter crop, starting 4 – 8 weeks before the first fall frost. They are hardy down to 25°F and don’t bolt in the cool, short days.

The key to success as a winter crop is for the plants to get big enough before cool weather hits. They will then continue to grow throughout the winter. If they are not big enough, they will just sit there looking sorry for themselves.

Spinach won’t take hard frost unprotected, so in harsher climates it is often grown under the cover of cloches, cold frames or poly tunnels. 

Planting

Direct sowing: This is easier than using transplants and generally more satisfactory. Sow the seed ½˝ deep (¼˝ in cold soil) and 1 – 2˝ apart (either broadcast or in wide rows).

Spinach sown directly into cold spring soil is slow to germinate, so some gardeners pre-germinate it before planting. Alternatively you could warm the soil with plastic mulch or cloches. Some gardeners mark the location of the slow germinating seeds by sowing a few radishes along with the spinach.

Thinning: When all of the plants have emerged, thin them to 2 – 4˝ apart. When they are 4˝ high thin them again to a final spacing of 4 – 8˝ (eat any thinnings that are big enough to be worthwhile). Spinach doesn’t like being overcrowded and will often react by bolting.

Transplants

Starting inside: Spinach doesn’t like transplanting (it can cause bolting), so this is only done under special circumstances. You might do it when you want to get an early start to the season, or in late summer, to give it cooler conditions than it would get outside.

To minimize root disturbance you should use cell packs or soil blocks. You can also multi-plant it by putting several seeds in each cell.

The plants germinate and grow best in cool conditions, so don’t let them get too warm, otherwise they may not perform well when transplanted outdoors.

Spacing: A single spinach plant doesn’t produce a lot, so you need quite a few plants to keep yourself supplied with spinach.

Beds: Spinach works well when grown in a wide bed, though it should be spaced carefully to avoid overcrowding. The exact spacing will vary according to the soil and the variety grown, but generally the following is good:

8˝ (poor soil)

6˝ (average soil)

4˝ (good soil)

Rows: Space the plants 2 – 5˝ apart, in rows 12 – 24˝ apart. If growing rows on a wide bed you could plant 3 or 4 rows 10˝ apart. .

Care

Spinach must grow quickly to produce the highest quality food. This means giving it optimal conditions; as much water and nutrients as it requires and no competition from weeds or crowded neighbors (all these factors can contribute to bolting).

Water: Keep the soil evenly moist (not wet) otherwise the plants may bolt. Fortunately this isn’t usually a problem in the cool weather preferred by spinach.

Spinach is vulnerable to fungus disease so it is good to keep the leaves dry when watering. Use drip irrigation, or water early enough so leaves can dry out quickly and not stay wet all night.

Fertilization: Spinach needs a good supply of nitrogen for best growth, but it grows in cold soil when not much nitrogen is readily available. If your soil isn’t very fertile you should give the plants a feed of compost tea, or liquid seaweed, every 2 weeks. You really want to keep those plants growing rapidly.

Problems

Pests: Pests aren’t usually a huge problem in the cool weather that spinach prefers. Slugs and snails, flea beetles and caterpillars will all eat the leaves, but the commonest are leaf miners. These tunnel into the leaves and make them useless. Remove any affected leaves (or squash the tiny grubs) and rub off the egg clusters. If they are very bad you will have to use row covers.

Aphids and leafhoppers can sometimes be a problem because they transmit virus diseases.

Many animal pests will go for spinach, particularly rabbits and deer.

Disease: Downy mildew is the commonest disease problem, though anthracnose, curly top and mosaic virus can all afflict spinach. Keep the leaves dry and provide good air circulation to minimize problems.

Bolting: Spinach will bolt when the day length is from 12 ½ – 15 hours (the exact number depends upon the variety, some are more sensitive than others). As with lettuce, warm weather (above 75°F) may hasten bolting, but doesn’t really cause it. Poor soil, overcrowding, vernalization may also cause the plants to bolt.

Cool weather (below 65°F) may retard bolting, as can frequent harvesting of leaves.

Nutrient deficiency: Spinach is somewhat vulnerable to a boron deficiency, which shows itself as small yellowish leaves and dark colored roots.

Harvesting

When: You can gather whole plants (harvest thin to begin with), or you can pick individual leaves (carefully) as soon as they are of sufficient quantity and size (3 – 4˝). Don’t take too many leaves from any one plant and don’t let them get larger than 6˝. You can also cut the whole plants, leaving a couple of inches to regenerate so you can harvest again at a later date,

Once the plants start producing you should harvest regularly and enthusiastically, Spinach doesn’t usually stay in peak condition for very long, so take advantage of it.

The flavor of fall spinach is improved by cool weather and even light frost. It can also be harvested for a lot longer and is less inclined to bolt.

When spinach gets ready to flower the top leaves become noticeably triangular and the stem elongates. When you see this starting to happen you should harvest as much as you can.

How: Pinching out the leaves encourages new growth, so keep it cropped even if you don’t need it (freeze it). If the leaves get too big and tough, try cutting the whole top off of the plant, leaving about 3˝ to  re-sprout.

Storage: Use the leaves as soon as possible after harvest, as they will only last for a few days in a plastic bag in the fridge. If you can’t use them immediately then freeze for later use.

Seed saving: Spinach plants are dioecious (there are separate male and female plants) so all plants don’t produce seed. The first plants to flower are males, which are taller but have smaller leaves. You don’t need a lot of males, but some are necessary for fertilization (1 male for every 2 females).

Spinach is wind pollinated, so it is hard to keep it pure (it must be isolated from other varieties by at least a mile). This essentially means only having one variety flowering at a time (of course you can’t do anything about other plants in the neighborhood). Because of this it is best to grow the plants in a cage covered in row cover fabric – it needs to be able to exclude very fine pollen)

Saving the seed is fairly straightforward, just allow a patch of plants to bolt (remove any plants that bolt earlier than the rest, or are unusual in any way) and let the seed ripen and dry on the plant. Then put the seed heads in a paper bag and allow them to dry completely indoors.

One female plant can produce a lot of seed, so you don’t need many plants. Only save seed from your best plants of course. Ideally you would save seed from at least 20 plants to maintain genetic variability.

Unusual growing ideas

Intercrop: When grown in ideal conditions, spinach is very fast growing and makes a useful crop for interplanting between slower maturing crops.

Salad mix: This fast growing plant makes an excellent salad mix crop. Sow the seeds ½ – 1˝ apart. Individual leaves are gathered as they reach a useful size (anywhere from 2 – 5˝). These are carefully pinched off (or snipped), leaving enough behind to enable the plant to regenerate. Spinach works very well when grown in this way, as bolting isn’t as much of a problem. See Salad Mix for more on this.

Winter crop: Spinach is very cold tolerant and makes a good winter crop for the cool greenhouse or growing frame. If you are lucky it may grow all winter without bolting.

Varieties

Many modern spinach varieties are lower in oxalic acid, as well as being more bolt resistant. You will have to experiment to find the best types for your area. Spinach is sometimes divided into smooth and wrinkled leaf (savoyed) types.

Smooth leaf: The leaves are lighter in color and fairly flat, which makes them easy to clean. This is the most popular type on the west coast. It is commonly used for salads and as baby greens.

Monstreaux De Viroflay – An old French heirloom with big leaves, does well in winter (50 days).

Red cardinal f1 – Red veined – bolts quickly – for baby leaves (30 days).

Giant Noble – Slow to bolt (45 days)

Oriental Giant F1 – Vigorous plant with big leaves (35 days)

Monnopa – Low oxalic acid (45 – 55 days)

Wrinkled leaf (savoyed): These have darker, wrinkled (obviously) leaves that are harder to clean than the smooth types. They do better in colder weather and tend to be slightly slower to bolt.

Bloomsdale Long Standing – A classic old variety (40 – 60 days).

Giant Winter – A very cold hardy type (45 days).

Merlo Nero – Italian heirloom (48 days)

Hybrids:

Emu F1 – The most bolt resistant type (42 days).

Regiment F1 – Productive, bolt and mildew resistant (40 days)

Tyee F1 – Bolt and mildew resistant (40 days)

Correnta F1 – Heat tolerant and bolt resistant for a longer harvest (45 days).

Kitchen use

Spinach must be washed carefully to get all of the soil off the leaves. This is especially important with the wrinkled leaf varieties.

The nutrients in spinach are easily leached out by boiling water, so they should only be cooked for a short time. The best way to leach out the maximum amount of oxalic acid, while losing the minimum nutrients is to boil for one minute in a large volume of boiling water in an uncovered pot.

I like to use spinach raw in salads. The smooth leaved varieties are considered superior for this, as they are easier to clean.

Spanakopita  

2 lb spinach
¼ cup parsley
1 oz dill leaves
1 cup crumbled feta cheese
½ cup ricotta cheese
4 tbsp olive oil
1 large onion, chopped
1 bunch green onions
4 cloves garlic, minced
2 eggs, beaten
10 sheets phyllo dough
¼ cup olive oil  

Sauté the onions, green onions and garlic in olive oil until translucent.
Add spinach and chopped parsley, cook until wilted and then leave to
cool.

Mix the beaten eggs, dill, feta and ricotta cheese and then stir in the
onion and spinach mix. Oil and layer 5 sheets of phyllo dough into a 9˝
square pan, then spread in the spinach cheese mix. Fold edges over mix
and then oil and layer the other 5 sheets of phyllo dough on top. Fold
edges down into pan to seal. Bake in preheated 350°F oven for 30 minutes until golden brown.  

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